Clinical Approach to Low Mood

Comprehensive Practical Framework

1
Symptom Overview
Overview
2
Pathophysiology
Mechanism
3
History Taking
History
4
Physical Examination
Examination
5
Differential Diagnosis
Differential
6
Investigations
Workup
7
Clinical Decision-Making
Algorithm
8
Pearls and Pitfalls
Summary

1. Symptom Overview

Understanding the clinical significance and classification of low mood

Low mood is one of the most common presenting complaints in primary care, with depression affecting approximately 280 million people worldwide. Major depressive disorder affects roughly 7% of adults in any given year and is the leading cause of disability globally. In primary care settings, depressive symptoms are present in up to 10-15% of all patient encounters, yet approximately 50% of cases remain undiagnosed. The lifetime risk of developing a depressive episode is approximately 15-20%, with women affected twice as often as men.

Definition

Low mood refers to a persistent state of sadness, emptiness, hopelessness, or emotional flatness that represents a change from a person’s baseline emotional state. While transient low mood is a normal human experience in response to life stressors, clinically significant low mood persists beyond what would be expected, causes functional impairment, and often occurs alongside other neurovegetative symptoms such as sleep disturbance, appetite changes, and cognitive difficulties.

Classification by Duration

Category	Duration	Common Causes	Clinical Significance
Transient	Less than 2 weeks	Normal grief reaction, acute stress, adjustment to life changes, sleep deprivation	Usually self-limiting; monitor for progression; provide supportive counseling
Subacute	2 to 4 weeks	Prolonged adjustment reaction, emerging depressive episode, subsyndromal depression	Warrants close follow-up; may meet criteria for depressive episode; consider intervention
Chronic	Greater than 4 weeks	Major depressive disorder, persistent depressive disorder (dysthymia), medical causes	High likelihood of diagnosable mood disorder; requires comprehensive assessment and treatment

Classification by Character

Reactive (Exogenous) Depression

Description: Low mood clearly triggered by identifiable life events or stressors such as bereavement, job loss, relationship breakdown, or medical diagnosis.

Clinical features: Mood may improve temporarily with positive events or distraction; patient can often identify “why” they feel depressed; onset correlates with stressor timing.

Implications: May respond well to psychotherapy and supportive interventions; addresses underlying stressor when possible.

Endogenous (Melancholic) Depression

Description: Low mood arising without clear external precipitant, often described as “coming from within” or qualitatively different from normal sadness.

Clinical features: Pervasive anhedonia; mood non-reactive to positive stimuli; prominent diurnal variation (worse in morning); significant neurovegetative symptoms.

Implications: Often suggests more biological etiology; typically shows stronger response to pharmacotherapy; may require combination treatment.

Classification by Associated Features

Subtype	Key Features	Clinical Significance
With Melancholic Features	Profound anhedonia, worse in morning, early morning awakening, psychomotor changes, excessive guilt, weight loss	Often responds better to pharmacotherapy than psychotherapy alone; tricyclics may be particularly effective
With Atypical Features	Mood reactivity preserved, increased sleep (hypersomnia), increased appetite or weight gain, leaden paralysis, rejection sensitivity	May respond preferentially to monoamine oxidase inhibitors or selective serotonin reuptake inhibitors; lifestyle modifications important
With Anxious Distress	Prominent tension, restlessness, worry, fear of losing control, sense of impending doom	Associated with longer duration, greater functional impairment, and increased suicide risk; may require anxiolytic augmentation
With Psychotic Features	Delusions (often mood-congruent themes of guilt, worthlessness, nihilism) or hallucinations	Requires urgent psychiatric referral; antidepressant alone insufficient; antipsychotic augmentation or electroconvulsive therapy often needed

Classification by Pattern and Timing

Pattern	Description	Suggests
Diurnal Variation (Morning Worse)	Mood lowest upon waking, gradually improves throughout the day	Melancholic depression; disrupted circadian rhythm; may benefit from morning light therapy
Diurnal Variation (Evening Worse)	Mood deteriorates as day progresses; worst in evening	Atypical depression; anxiety-predominant presentation; fatigue-related mood decline
Seasonal Pattern	Recurrent episodes at specific times of year, typically autumn/winter with remission in spring/summer	Seasonal affective disorder; light therapy highly effective; vitamin D assessment warranted
Peripartum Onset	Onset during pregnancy or within 4 weeks postpartum	Peripartum depression; requires screening for infanticidal/suicidal ideation; affects bonding; urgent treatment needed
Perimenstrual Pattern	Mood symptoms consistently worsen in luteal phase, resolve shortly after menses	Premenstrual dysphoric disorder if severe; hormonal factors; symptom tracking over 2 cycles confirms
Episodic with Full Interepisode Recovery	Discrete episodes of depression with return to baseline between episodes	Major depressive disorder, recurrent; identifies need for maintenance treatment after multiple episodes
Chronic Persistent	Continuous low-grade depression lasting 2 years or more	Persistent depressive disorder (dysthymia); often responds to combination of medication and psychotherapy

Key Concept: The “Rule Out” Priorities

When evaluating low mood, three categories must always be considered:

Safety First: Suicidal ideation, psychotic features, and severe functional impairment require urgent assessment
Bipolar Screening: Up to 40% of patients initially diagnosed with depression actually have bipolar disorder; always screen for lifetime history of manic or hypomanic episodes
Medical Causes: Approximately 10-15% of depression cases have an underlying medical etiology; thyroid dysfunction, anemia, vitamin deficiencies, and medication side effects are common and treatable

Impact on Quality of Life

Depression ranks among the top causes of years lived with disability worldwide. Beyond emotional suffering, low mood significantly impacts occupational functioning (increased absenteeism and presenteeism), relationships and social connections, physical health outcomes (increased cardiovascular risk, impaired immune function), and healthcare utilization. Early recognition and appropriate treatment can substantially reduce this burden.

2. Pathophysiology and Mechanisms

Understanding the underlying mechanisms of low mood and depression

Depression is a heterogeneous condition resulting from complex interactions between genetic vulnerability, neurobiological changes, psychological factors, and environmental stressors. No single mechanism explains all cases, and understanding the multiple pathways helps guide individualized treatment selection. The current understanding integrates several complementary hypotheses that have evolved from the original monoamine theory to encompass neuroplasticity, inflammation, and circuit-based models.

Neurotransmitter Systems in Depression

Neurotransmitter	Normal Function	Role in Depression	Treatment Implications
Serotonin (5-HT)	Mood regulation, sleep-wake cycles, appetite, impulse control, pain modulation	Reduced serotonergic transmission in depression; associated with anxiety, irritability, and suicidal behavior	Selective serotonin reuptake inhibitors (SSRIs) are first-line treatment; tryptophan depletion can precipitate relapse
Norepinephrine (NE)	Alertness, energy, attention, stress response, motivation	Deficiency associated with fatigue, psychomotor retardation, impaired concentration	Serotonin-norepinephrine reuptake inhibitors (SNRIs) and norepinephrine-dopamine reuptake inhibitors target this system
Dopamine (DA)	Reward processing, motivation, pleasure, motor function	Reduced dopaminergic function contributes to anhedonia, apathy, and psychomotor slowing	Bupropion enhances dopamine; atypical antipsychotics modulate dopamine in treatment-resistant cases
Glutamate	Primary excitatory neurotransmitter; learning, memory, synaptic plasticity	Excess glutamate may cause excitotoxicity; NMDA receptor dysfunction implicated in depression	Ketamine and esketamine act on glutamate system; rapid antidepressant effects
GABA	Primary inhibitory neurotransmitter; anxiety regulation, sleep	Reduced GABAergic tone in depression; contributes to anxiety and sleep disturbance	Benzodiazepines provide short-term relief; some antidepressants enhance GABA function indirectly

Neural Circuits and Brain Regions

Prefrontal Cortex

Normal function: Executive function, emotional regulation, decision-making, working memory

In depression: Reduced activity in dorsolateral prefrontal cortex; impaired top-down control of emotional responses

Clinical relevance: Explains cognitive symptoms (poor concentration, indecisiveness); target for transcranial magnetic stimulation

Amygdala

Normal function: Threat detection, fear processing, emotional memory formation

In depression: Hyperactivity and increased reactivity to negative stimuli; enhanced negative emotional processing

Clinical relevance: Explains negativity bias, rumination, and anxiety symptoms; normalizes with effective treatment

Hippocampus

Normal function: Memory consolidation, contextual learning, stress regulation via hypothalamic-pituitary-adrenal axis feedback

In depression: Volume reduction (up to 10-15%); impaired neurogenesis; weakened stress regulation

Clinical relevance: Memory complaints common; antidepressants promote hippocampal neurogenesis; volume may recover with treatment

Hypothalamic-Pituitary-Adrenal Axis Dysregulation

Component	Normal Function	Dysfunction in Depression
Hypothalamus	Releases corticotropin-releasing hormone (CRH) in response to stress	Elevated CRH levels; increased CRH gene expression; enlarged hypothalamus in severe depression
Pituitary	Releases adrenocorticotropic hormone (ACTH) in response to CRH	Blunted ACTH response to CRH challenge; pituitary enlargement in chronic depression
Adrenal Cortex	Releases cortisol in response to ACTH	Hypercortisolemia in 40-60% of severely depressed patients; adrenal hypertrophy
Feedback Mechanism	Cortisol inhibits further CRH and ACTH release (negative feedback)	Impaired glucocorticoid receptor sensitivity; failed dexamethasone suppression test; chronic stress exposure

Clinical Pearl: Chronic cortisol elevation contributes to hippocampal atrophy, immune suppression, insulin resistance, and visceral fat accumulation. This helps explain the bidirectional relationship between depression and conditions such as diabetes, cardiovascular disease, and metabolic syndrome.

Neuroplasticity and Neurotrophic Factors

Brain-Derived Neurotrophic Factor (BDNF)

Normal role: Supports neuronal survival, growth, and synaptic plasticity
In depression: Serum BDNF levels reduced by 20-30%
Treatment effect: Antidepressants increase BDNF expression over weeks
Clinical note: Time lag in BDNF normalization may explain delayed therapeutic response

Synaptic Connections

In depression: Reduced dendritic branching and spine density in prefrontal cortex
Consequence: Impaired neural connectivity and information processing
Recovery: Effective treatment promotes synaptogenesis
Rapid-acting agents: Ketamine rapidly increases synaptic connections within hours

Inflammatory Mechanisms

The Inflammation-Depression Connection

Approximately 30% of depressed patients show elevated inflammatory markers. Chronic inflammation affects mood through multiple pathways:

Tryptophan metabolism: Inflammatory cytokines activate indoleamine 2,3-dioxygenase (IDO), shunting tryptophan away from serotonin synthesis toward kynurenine pathway
Neurotransmitter effects: Cytokines reduce monoamine availability and increase glutamate
HPA activation: Interleukins stimulate the hypothalamic-pituitary-adrenal axis
Neuroplasticity impairment: Inflammation reduces BDNF and impairs neurogenesis

Clinical relevance: Patients with elevated C-reactive protein (CRP) may respond better to anti-inflammatory strategies or agents with anti-inflammatory properties.

How Conditions Cause Low Mood

Condition	Mechanism	Treatment Implication
Hypothyroidism	Thyroid hormones modulate serotonin and norepinephrine systems; deficiency reduces neurotransmitter synthesis and receptor sensitivity	Screen all depressed patients; thyroid replacement may resolve depression without antidepressants; T3 augmentation may enhance antidepressant response
Vitamin B12 Deficiency	Required for methylation reactions in monoamine synthesis; deficiency impairs serotonin, norepinephrine, and dopamine production	Check B12 levels especially in elderly, vegetarians, and those on metformin; supplementation can improve mood even with “low-normal” levels
Vitamin D Deficiency	Vitamin D receptors present in mood-regulating brain regions; influences serotonin synthesis and inflammatory pathways	Associated with seasonal affective disorder; supplementation may augment antidepressant effects; target serum level above 30 ng/mL
Chronic Pain Conditions	Shared neural pathways between pain and mood; chronic pain depletes monoamines; opioid system dysregulation	Treat pain and depression concurrently; duloxetine and amitriptyline address both; avoid excessive opioid use
Beta-Blocker Use	Lipophilic beta-blockers cross blood-brain barrier; reduce noradrenergic tone; may affect melatonin secretion	Consider switching to less lipophilic agent (e.g., atenolol); weigh cardiovascular benefits against mood effects
Corticosteroid Use	Exogenous steroids disrupt hypothalamic-pituitary-adrenal axis feedback; cause hippocampal changes; affect multiple neurotransmitter systems	Psychiatric effects dose-dependent; taper when possible; mood usually improves with dose reduction
Sleep Apnea	Chronic intermittent hypoxia; sleep fragmentation; oxidative stress; inflammation; disrupted sleep architecture	Screen with STOP-BANG; treatment with continuous positive airway pressure often improves mood significantly
Post-Stroke	Direct lesion effects on mood circuits; disruption of monoamine pathways; inflammation; psychological adjustment	Affects up to 30% of stroke survivors; left frontal lesions higher risk; early antidepressant treatment may improve functional recovery

Often Overlooked Mechanism: Gut-Brain Axis

The gut microbiome influences mood through multiple pathways: production of neurotransmitter precursors (90% of serotonin is produced in the gut), modulation of inflammation, regulation of the hypothalamic-pituitary-adrenal axis via the vagus nerve, and production of short-chain fatty acids that affect brain function. Patients with depression often show reduced microbial diversity. This emerging understanding supports the role of diet in depression management and opens possibilities for probiotic interventions, though evidence for specific recommendations remains limited.

Genetic and Epigenetic Factors

Genetic Vulnerability

Heritability: Depression is approximately 40% heritable based on twin studies

Gene-environment interaction: Serotonin transporter gene (5-HTTLPR) short allele increases depression risk following life stress

Polygenic nature: Hundreds of genes contribute small effects; no single “depression gene” exists

Epigenetic Modifications

Mechanism: Early life adversity causes lasting changes in gene expression without altering DNA sequence

Examples: Increased methylation of glucocorticoid receptor gene; altered BDNF expression

Clinical relevance: Helps explain increased depression risk with childhood trauma; potentially reversible with treatment

3. History Taking

A comprehensive approach to eliciting the low mood history

Red Flags — Require Urgent Evaluation

Suicidal ideation with plan or intent — Immediate safety assessment; consider hospitalization
Psychotic features — Delusions, hallucinations suggest severe depression or other diagnosis
Recent suicide attempt or self-harm — High risk for repeat attempt
Severe functional decline — Unable to care for self, not eating/drinking

Command hallucinations — Voices instructing self-harm require urgent intervention
Access to lethal means — Firearms, stockpiled medications increase risk
Recent major loss or humiliation — Acute stressor with hopelessness
History of prior suicide attempts — Strongest predictor of future attempts

Systematic History: The “SAD CAGES” Approach

Use the mnemonic “SAD CAGES” to ensure comprehensive history taking for low mood:

S — Sadness and Mood: “How would you describe your mood? How long have you been feeling this way?”
A — Anhedonia: “Are you still able to enjoy things you used to enjoy? What brings you pleasure now?”
D — Duration and Course: “When did this start? Has it been constant or does it come and go?”
C — Concentration and Cognition: “How is your concentration? Are you able to make decisions?”
A — Appetite and Weight: “Has your appetite changed? Have you lost or gained weight without trying?”
G — Guilt and Worthlessness: “Do you feel guilty about things? Do you feel you are a burden to others?”
E — Energy and Psychomotor: “How are your energy levels? Do you feel slowed down or more restless than usual?”
S — Sleep and Suicidality: “How is your sleep? Have you had any thoughts of harming yourself or not wanting to be alive?”

Suicide Risk Assessment — Essential Questions

Always Ask — Asking Does NOT Increase Risk

Use a stepped approach to assess suicidal ideation:

Passive ideation: “Have you had thoughts that life isn’t worth living, or wished you wouldn’t wake up?”
Active ideation: “Have you had thoughts of actually ending your life or harming yourself?”
Plan: “Have you thought about how you might do it?”
Intent: “Do you intend to act on these thoughts?”
Means: “Do you have access to [method mentioned]?”
Protective factors: “What has kept you from acting on these thoughts?”

Targeted Questions by Suspected Cause

Suspected Cause	Key Features	Ask This Question
Major Depressive Disorder	Persistent low mood, anhedonia, neurovegetative symptoms for ≥2 weeks	“Have you experienced a period of at least two weeks where you felt down most of the day, nearly every day?”
Bipolar Disorder	History of elevated mood, decreased need for sleep, increased energy, risky behavior	“Have you ever had a period where you felt unusually high, energetic, or irritable, needed much less sleep, and maybe did things that were out of character?”
Persistent Depressive Disorder (Dysthymia)	Chronic low-grade depression for ≥2 years, “always been this way”	“Have you felt mildly depressed or down more days than not for the past two years or longer?”
Adjustment Disorder	Clear temporal relationship to identifiable stressor, symptoms within 3 months of stressor	“Did something specific happen around the time you started feeling this way? A loss, a change, a disappointment?”
Seasonal Affective Disorder	Recurrent pattern in fall/winter, atypical features (hypersomnia, carbohydrate craving)	“Do you notice your mood gets worse at the same time each year, particularly in the darker months?”
Hypothyroidism	Fatigue, weight gain, cold intolerance, constipation, dry skin	“Have you noticed feeling more tired, cold, or constipated? Any changes to your skin or hair?”
Sleep Apnea	Snoring, witnessed apneas, daytime sleepiness, morning headaches	“Has anyone told you that you snore loudly or stop breathing in your sleep? Do you wake up feeling unrefreshed?”
Substance Use Disorder	Alcohol or drug use, withdrawal symptoms, mood fluctuations with use	“How much alcohol do you drink in a typical week? Have you used any recreational drugs? Does your mood change when you drink or use?”
Grief Reaction	Recent bereavement, waves of sadness, preoccupation with deceased, preserved self-esteem	“Have you experienced a significant loss recently? How has that been affecting you?”
Medication-Induced	Temporal relationship to medication initiation, resolution with discontinuation	“Have you started any new medications recently? Did your mood change after starting [specific medication]?”

Critical: Screen Every Patient for Bipolar Disorder

Up to 40% of patients initially diagnosed with unipolar depression actually have bipolar disorder. Missing this diagnosis leads to:

Antidepressant monotherapy, which can trigger mania or rapid cycling
Treatment resistance and multiple medication trials
Delayed appropriate treatment by an average of 8-10 years

Key screening question: “Have you ever had a period lasting at least a few days where you felt the opposite of depressed — unusually energetic, needed much less sleep than normal but didn’t feel tired, talked more than usual, or did impulsive things you later regretted?”

Medication and Substance History

Medications That Can Cause Low Mood

Beta-blockers — Especially lipophilic agents (propranolol, metoprolol); fatigue and mood changes
Corticosteroids — Dose-dependent; both depression and mania possible
Interferons — High rates of depression with interferon-alpha therapy
Isotretinoin — Controversial but monitor mood during treatment
Hormonal contraceptives — Some individuals sensitive; consider progestin type
Antiepileptics — Levetiracetam, topiramate, vigabatrin, barbiturates
Benzodiazepines — Chronic use or withdrawal can worsen mood
Opioids — Chronic use associated with depression; withdrawal causes dysphoria
Proton pump inhibitors — May reduce B12 absorption over time
Statins — Rare but reported; mechanism unclear

Substance Use Considerations

Alcohol: Depressant; use AUDIT-C screening; depression common during heavy use and withdrawal
Cannabis: Amotivational syndrome; may worsen or trigger depression in vulnerable individuals
Stimulants: Crash and withdrawal cause profound depression; “comedown” after use
Opioids: Chronic use linked to depression; assess for opioid use disorder
Caffeine: Withdrawal causes fatigue and low mood; excessive use disrupts sleep

Past Treatment History

Prior antidepressants: What worked? What didn’t? Why stopped?
Psychotherapy: Type, duration, perceived helpfulness
Hospitalizations: Number, circumstances, treatments received

Social and Contextual History

Domain	Key Questions	Relevance
Relationships and Support	“Who do you live with? Who can you talk to when things are difficult? How are your important relationships?”	Social isolation is both a risk factor and consequence of depression; strong support improves outcomes
Occupation and Finances	“Are you working? How is work going? Are you having financial difficulties?”	Job loss, workplace stress, and financial strain are common precipitants; functional impairment at work indicates severity
Early Life and Trauma	“Did you experience any difficult events growing up? Any history of abuse or neglect?”	Adverse childhood experiences increase depression risk; trauma-informed care may be needed
Recent Life Events	“Have there been any major changes or losses in your life recently?”	Bereavement, divorce, job loss, diagnosis of illness are common triggers; informs adjustment disorder diagnosis
Daily Functioning	“Walk me through a typical day. Are you able to do your usual activities?”	Assesses severity and functional impairment; neglect of hygiene, responsibilities indicates severe depression

Family Psychiatric History

Key questions for family history:

“Has anyone in your family experienced depression or other mental health conditions?”
“Has anyone in your family attempted or died by suicide?”
“Has anyone in your family been diagnosed with bipolar disorder or had periods of being ‘too high’?”
“Has anyone in your family been hospitalized for psychiatric reasons?”
“Do you know if any family members responded well or poorly to specific antidepressants?”

Why it matters: Family history of bipolar disorder increases suspicion for bipolar in the patient. Family history of antidepressant response may guide medication selection. Completed suicide in family significantly increases patient’s risk.

4. Physical Examination

A systematic approach for patients presenting with low mood

Systematic Framework: The physical examination in depression serves two purposes: (1) identifying medical conditions that may cause or contribute to low mood, and (2) assessing for physical manifestations of depression itself. Use a “General to Specific” approach, beginning with observation of appearance and behavior before proceeding to targeted system examination.

Mental Status Examination — Core Components

Component	What to Assess	Findings Suggestive of Depression
Appearance	Grooming, hygiene, dress, posture, eye contact	Disheveled, poor hygiene, weight change evident, slumped posture, poor eye contact, psychomotor slowing or agitation visible
Behavior	Activity level, cooperation, unusual movements	Psychomotor retardation (slowed movements, long latency to respond), psychomotor agitation (restlessness, hand-wringing, pacing)
Speech	Rate, rhythm, volume, tone, spontaneity	Decreased rate and volume, monotonous tone, increased response latency, poverty of speech, sighing
Mood	Patient’s subjective description of emotional state	“Sad,” “empty,” “hopeless,” “numb,” “nothing” — document in patient’s own words
Affect	Observed emotional expression: range, reactivity, congruence	Constricted or flat affect, tearfulness, mood-congruent (sad affect with sad mood), reduced reactivity
Thought Content	Suicidal/homicidal ideation, delusions, obsessions, preoccupations	Suicidal ideation, excessive guilt, worthlessness, hopelessness, rumination; in severe cases: nihilistic or somatic delusions
Thought Process	Organization, logic, goal-directedness	Usually linear but may be slowed; poverty of thought content; rumination on negative themes
Perception	Hallucinations (auditory, visual), illusions	Usually absent; if present (typically auditory, derogatory content), indicates psychotic depression requiring urgent referral
Cognition	Orientation, attention, concentration, memory	“Pseudodementia” — subjective cognitive complaints, poor concentration, may perform poorly on testing but improves with encouragement
Insight and Judgment	Awareness of illness, understanding of need for treatment	Variable; may have good insight but feel hopeless about recovery; impaired judgment in severe cases

General Inspection

Overall appearance: Does the patient appear their stated age? Signs of self-neglect? Appropriateness of dress for season and setting?
Body habitus: Evidence of recent weight loss (loose clothing, temporal wasting) or weight gain? Obesity suggesting possible sleep apnea?
Activity level: Psychomotor retardation (slowed, effortful movements) or agitation (fidgeting, unable to sit still)?
Skin: Pallor (anemia), jaundice (liver disease), dry skin (hypothyroidism), evidence of self-harm (scars, fresh injuries on forearms, thighs)?
Nutritional status: Cachexia suggesting severe depression, malignancy, or other chronic illness?

Vital Signs

Vital Sign	What to Look For	Clinical Significance
Heart Rate	Tachycardia, bradycardia, irregularity	Tachycardia: anxiety, hyperthyroidism, stimulant use, withdrawal. Bradycardia: hypothyroidism, beta-blocker use, severe debility
Blood Pressure	Hypertension, hypotension, orthostatic changes	Orthostatic hypotension may indicate dehydration from poor intake; baseline BP important before starting antidepressants
Weight and BMI	Compare to previous weights; calculate BMI	Significant weight loss (>5% in 1 month) or gain; obesity as risk factor for sleep apnea; baseline for medication monitoring
Temperature	Fever, hypothermia	Fever suggests infection which can cause delirium or mood changes; hypothermia in severe hypothyroidism or severe self-neglect
Respiratory Rate	Tachypnea, sighing respirations	Frequent sighing common in depression; tachypnea may indicate anxiety or underlying cardiopulmonary disease

Head and Neck Examination

Eyes

Conjunctival pallor: Anemia
Scleral icterus: Liver disease, hemolysis
Lid lag, exophthalmos: Hyperthyroidism
Periorbital edema: Hypothyroidism, nephrotic syndrome
Pupil changes: Constricted (opioid use), dilated (stimulant use, withdrawal)

Thyroid

Goiter: Hypo- or hyperthyroidism
Nodules: May indicate thyroid dysfunction
Tenderness: Thyroiditis
Texture: Smooth (Graves), irregular (multinodular)

Always palpate the thyroid — thyroid disorders are common, treatable causes of mood symptoms.

Oropharynx

Dental hygiene: Poor dental care may indicate self-neglect; dental pain can contribute to depression
Glossitis: Smooth, red tongue suggests B12 or folate deficiency
Dry mucous membranes: Dehydration from poor oral intake
Mallampati score: High score suggests obstructive sleep apnea risk

Neurological Examination

Component	What to Assess	Clinical Significance
Cranial Nerves	Facial symmetry, visual fields, extraocular movements	Focal findings suggest structural lesion; may indicate stroke (post-stroke depression)
Motor Function	Tone, strength, tremor, bradykinesia	Cogwheel rigidity, bradykinesia, resting tremor suggest Parkinson disease (depression common); fine tremor may indicate hyperthyroidism or anxiety
Reflexes	Deep tendon reflexes, plantar responses	Hyporeflexia with delayed relaxation phase suggests hypothyroidism; hyperreflexia may indicate B12 deficiency
Sensation	Light touch, proprioception, vibration sense	Peripheral neuropathy pattern suggests B12 deficiency or diabetes
Gait and Balance	Gait pattern, Romberg test, tandem walking	Shuffling gait (Parkinson), ataxia (B12 deficiency, alcohol), magnetic gait (normal pressure hydrocephalus)
Cognitive Screen	Mini-Mental State Examination or Montreal Cognitive Assessment	Helps distinguish depression from dementia; depressed patients often underperform but improve with encouragement

Cardiovascular Examination

Heart sounds: Murmurs, S3, S4 — heart failure can cause fatigue and low mood
Jugular venous pressure: Elevation suggests heart failure
Peripheral edema: Heart failure, nephrotic syndrome, hypothyroidism
Peripheral pulses: Reduced in peripheral vascular disease (associated with depression via shared cardiovascular risk)

Respiratory Examination

Inspection: Barrel chest (chronic obstructive pulmonary disease — depression is common comorbidity)
Auscultation: Wheezes, crackles — chronic lung disease contributes to reduced quality of life and mood
Signs of sleep apnea: Neck circumference >43 cm (17 inches) in men or >41 cm (16 inches) in women increases risk

Abdominal Examination

Hepatomegaly: Alcohol-related liver disease, malignancy
Ascites: Liver disease, malignancy
Tenderness: May indicate gastrointestinal pathology contributing to poor nutrition
Surgical scars: Previous bowel surgery may affect B12 absorption

Assessment for Self-Harm

Examine for Evidence of Self-Harm

Examine forearms, wrists, thighs, and abdomen for:

Fresh cuts or burns: Active self-harm behavior
Scars: Linear scars in parallel on forearms are characteristic; indicates history of cutting
Bruises: Especially in unusual locations (self-inflicted vs. abuse)
Wounds in various stages of healing: Suggests ongoing behavior

Ask permission before examining these areas. If findings present, ask non-judgmentally: “Can you tell me about these marks?”

Expected Findings by Etiology

Condition	General/Mental Status	Specific Physical Findings	Key Differentiating Features
Primary Major Depressive Disorder	Sad affect, psychomotor changes, poor eye contact	Often normal physical examination	Diagnosis relies on history and mental status; physical examination rules out secondary causes
Hypothyroidism	Slowed cognition, flat affect, fatigue	Goiter, dry skin, brittle hair, periorbital edema, bradycardia, delayed reflex relaxation, weight gain	Cold intolerance, constipation; symptoms develop insidiously
Hyperthyroidism	Anxiety, irritability, emotional lability	Goiter, tremor, warm moist skin, tachycardia, lid lag, exophthalmos (Graves), hyperreflexia	Heat intolerance, weight loss despite good appetite; may present as “apathetic thyrotoxicosis” in elderly
Vitamin B12 Deficiency	Cognitive slowing, memory impairment, apathy	Pallor, glossitis, peripheral neuropathy (stocking-glove), posterior column signs, ataxia	Neuropsychiatric symptoms may precede anemia; check methylmalonic acid if B12 borderline
Anemia (Iron Deficiency)	Fatigue, low energy, poor concentration	Pallor (conjunctiva, palms), koilonychia, angular cheilitis, atrophic glossitis, tachycardia	Fatigue prominent; pica or pagophagia may be present
Parkinson Disease	Masked facies, flat affect, cognitive slowing	Resting tremor, cogwheel rigidity, bradykinesia, shuffling gait, postural instability	Depression often precedes motor symptoms; affects 40-50% of patients
Sleep Apnea	Fatigue, irritability, poor concentration	Obesity, large neck circumference, crowded oropharynx, hypertension	Snoring, witnessed apneas, morning headaches, daytime sleepiness; STOP-BANG screening
Alcohol Use Disorder	Variable affect, may minimize symptoms	Spider angiomata, palmar erythema, gynecomastia, hepatomegaly, tremor	Mood improves after sustained abstinence; depression may be cause or consequence

Important Teaching Point

Normal physical examination is common! The majority of patients with primary depression will have entirely normal physical examination findings. The purpose of the physical examination is to:

Rule out medical conditions that can cause or contribute to depression (hypothyroidism, anemia, vitamin deficiencies)
Document baseline vital signs and weight before starting treatment
Assess for evidence of self-harm
Evaluate for signs of severe self-neglect
Identify contraindications to certain medications

A normal physical examination does not exclude significant depression; diagnosis rests primarily on history and mental status examination.

5. Differential Diagnosis

Systematic approach organized by probability and clinical features

The differential diagnosis of low mood extends beyond primary psychiatric disorders to include medical conditions, substance-related causes, and medication side effects. A systematic approach ensures treatable causes are not missed. Always consider the possibility of bipolar disorder before diagnosing unipolar depression, as this fundamentally changes management.

Primary Psychiatric Causes of Low Mood

Probability	Condition	Key Features	Red Flags
COMMON (approximately 60-70%)	Major Depressive Disorder	Low mood or anhedonia plus ≥4 other symptoms for ≥2 weeks; functional impairment	Suicidal ideation, psychotic features, severe weight loss, complete inability to function
COMMON	Adjustment Disorder with Depressed Mood	Symptoms within 3 months of identifiable stressor; does not meet full criteria for major depressive disorder; resolves within 6 months of stressor ending	Progression to major depressive disorder if symptoms persist or worsen
COMMON	Persistent Depressive Disorder (Dysthymia)	Chronic low-grade depression for ≥2 years; patient may say “I’ve always been this way”; fewer symptoms than major depressive disorder	“Double depression” — major depressive episode superimposed on dysthymia
LESS COMMON (approximately 20%)	Bipolar Disorder (Depressive Episode)	Depression indistinguishable from unipolar; history of manic or hypomanic episodes (may be unrecognized); family history of bipolar; early onset; multiple prior episodes	Antidepressant-induced mania, rapid cycling, mixed features, psychotic symptoms
LESS COMMON	Generalized Anxiety Disorder with Comorbid Depression	Excessive worry predominates; depression develops secondary to chronic anxiety; significant symptom overlap	Suicidal ideation increases when anxiety and depression co-occur
LESS COMMON	Grief Reaction (Uncomplicated Bereavement)	Follows loss of loved one; waves of sadness; preserved self-esteem; symptoms improve over weeks to months	Prolonged grief disorder if severe symptoms persist >12 months; suicidal ideation
UNCOMMON BUT SERIOUS (approximately 10%)	Major Depressive Disorder with Psychotic Features	Severe depression plus delusions (guilt, nihilism, somatic) or hallucinations; often mood-congruent content	High suicide risk; requires psychiatric referral; antidepressant alone insufficient
UNCOMMON BUT SERIOUS	Schizoaffective Disorder (Depressive Type)	Psychotic symptoms present even when mood symptoms absent; chronic course; prominent functional impairment	Requires specialist management; antipsychotic treatment essential

Step-by-Step Approach to Low Mood:

Step 1: Safety Assessment — Evaluate for suicidal ideation, psychotic features, and ability to care for self
Step 2: Rule Out Bipolar — Screen for lifetime history of mania or hypomania in every patient
Step 3: Consider Medical Causes — Thyroid, B12, anemia, sleep apnea, chronic disease
Step 4: Review Medications and Substances — Recent changes? Alcohol or drug use?
Step 5: Establish Duration and Severity — Meets criteria for major depressive disorder vs. adjustment disorder vs. dysthymia?
Step 6: Identify Comorbidities — Anxiety, personality factors, chronic pain often co-occur

Medical Conditions Causing Low Mood

Category	Condition	Approximate Frequency as Cause	Key Distinguishing Features
ENDOCRINE	Hypothyroidism	5-10% of depression cases	Fatigue, cold intolerance, weight gain, constipation, dry skin, bradycardia; may be subclinical
ENDOCRINE	Hyperthyroidism	2-5%	May present as anxiety or “apathetic thyrotoxicosis” in elderly; tremor, weight loss, tachycardia
ENDOCRINE	Diabetes Mellitus	Depression 2-3x more common in diabetics	Bidirectional relationship; glycemic control affects mood; depression impairs self-management
ENDOCRINE	Cushing Syndrome	Rare but important	Central obesity, moon facies, striae, hypertension, proximal weakness; depression in 50-80%
ENDOCRINE	Addison Disease	Rare	Fatigue, weight loss, hyperpigmentation, hypotension; can mimic depression
ENDOCRINE	Hyperparathyroidism	Uncommon	“Bones, stones, groans, and psychiatric moans”; elevated calcium; fatigue, cognitive changes
NUTRITIONAL	Vitamin B12 Deficiency	5-10% especially in elderly	Neuropsychiatric symptoms may precede anemia; paresthesias, cognitive decline; check in elderly, vegetarians, metformin users
NUTRITIONAL	Folate Deficiency	Less common than B12	Similar to B12 but without neurological features; macrocytic anemia; alcoholism, malabsorption
NUTRITIONAL	Iron Deficiency Anemia	Common contributor	Fatigue, pallor, poor concentration; may contribute to depression even without frank anemia
NUTRITIONAL	Vitamin D Deficiency	Associated but causation debated	More prevalent in northern latitudes; associated with seasonal affective disorder; check if risk factors present
NEUROLOGICAL	Parkinson Disease	Depression in 40-50% of patients	May precede motor symptoms by years; apathy, bradyphrenia; tremor, rigidity, bradykinesia
NEUROLOGICAL	Post-Stroke Depression	Affects 30% of stroke survivors	Left frontal lesions higher risk; onset within months of stroke; impairs rehabilitation
NEUROLOGICAL	Multiple Sclerosis	Depression in 50% over lifetime	May be presenting symptom; relapsing-remitting pattern; fatigue prominent
NEUROLOGICAL	Early Dementia	Depression common in prodromal phase	Late-onset depression may herald dementia; distinguish from “pseudodementia” of depression
NEUROLOGICAL	Normal Pressure Hydrocephalus	Rare but treatable	Triad: gait disturbance, urinary incontinence, cognitive decline; magnetic gait pattern
SLEEP	Obstructive Sleep Apnea	Underdiagnosed contributor	Fatigue, poor concentration, irritability; obesity, snoring, witnessed apneas; STOP-BANG screening
CHRONIC DISEASE	Chronic Pain Syndromes	High comorbidity (30-50%)	Bidirectional relationship; shared neural pathways; treat both concurrently
CHRONIC DISEASE	Heart Failure	Depression in 20-40%	Fatigue, reduced quality of life; depression worsens cardiac outcomes
CHRONIC DISEASE	Chronic Kidney Disease	Depression in 20-30%	Uremia affects cognition and mood; increases with disease severity
INFECTIOUS	Chronic Infections (HIV, Hepatitis C, Lyme)	Variable	Consider based on risk factors; HIV-associated neurocognitive disorder; interferon treatment for hepatitis C
MALIGNANCY	Occult Malignancy	Rare but important	Unexplained weight loss, fatigue, new depression in older adult; pancreatic cancer classically associated

Categorical Approach to Differential Diagnosis

Primary Psychiatric

Major Depressive Disorder

Bipolar Disorder (depressed phase)

Persistent Depressive Disorder

Adjustment Disorder

Anxiety Disorders with depression

Grief Reaction

Medical/Organic

Hypothyroidism / Hyperthyroidism

Vitamin B12 / Folate deficiency

Anemia

Sleep Apnea

Parkinson Disease

Chronic diseases (diabetes, heart failure)

Substance-Related

Alcohol Use Disorder

Cannabis Use

Stimulant Withdrawal

Opioid Use/Withdrawal

Benzodiazepine Withdrawal

Sedative-Hypnotic Use

Medication-Induced

Beta-blockers

Corticosteroids

Hormonal contraceptives

Interferons

Antiepileptics

Isotretinoin

Drug-Induced Low Mood

Drug or Drug Class	Mechanism	Characteristics	Time to Resolution After Stopping
Beta-blockers (lipophilic)	Central noradrenergic blockade; melatonin suppression; crosses blood-brain barrier	Fatigue, low mood, vivid dreams; propranolol and metoprolol higher risk than atenolol	Days to 2 weeks after discontinuation or switch
Corticosteroids	HPA axis disruption; hippocampal effects; neurotransmitter changes	Dose-dependent; can cause depression, mania, or psychosis; more common with higher doses and longer duration	Variable; may persist weeks after taper; gradual taper recommended
Interferon-alpha	Proinflammatory cytokines; tryptophan depletion via IDO activation	Depression in 30-50% of patients; typically onset within first 3 months of treatment	Weeks to months after completion; may require antidepressant treatment
Hormonal contraceptives	Effects on serotonin, GABA; varies by progestin type	Some individuals sensitive; adolescents may have higher risk; consider progestin type	1-3 months after discontinuation; may need to trial different formulation
Isotretinoin	Mechanism unclear; may affect retinoid receptors in brain	Controversial association; monitor mood during treatment; rare but serious reports	Variable; usually resolves after stopping but monitor closely
Levetiracetam	Unclear; possibly related to SV2A binding	Behavioral changes, irritability, depression; “levetiracetam rage”	Days to weeks after discontinuation
Topiramate	Multiple mechanisms; cognitive effects prominent	Cognitive dulling, word-finding difficulty, depression; dose-related	Weeks after dose reduction or discontinuation
Benzodiazepines (chronic use)	GABAergic tolerance; possible serotonergic effects	Depression more common with chronic use; withdrawal can cause severe dysphoria	Months; very gradual taper essential to minimize withdrawal depression
Opioids (chronic use)	Endogenous opioid system dysregulation; hormonal effects	Opioid-induced androgen deficiency; emotional blunting; withdrawal causes severe dysphoria	Weeks to months; may persist; address underlying pain and dependence
Proton pump inhibitors	May reduce B12 and magnesium absorption over time	Indirect effect via nutrient deficiency; usually with prolonged use	Check and correct deficiencies; reassess need for PPI
Statins	Mechanism unclear; cholesterol needed for steroid synthesis	Rare; case reports; usually mild; weigh cardiovascular benefits	Weeks; trial discontinuation if suspected but weigh risks
Varenicline	Partial nicotinic agonist; complex effects on mood	Earlier warnings; more recent data suggests risk similar to placebo; monitor	Days to weeks; nicotine withdrawal itself causes mood changes

Quick Reference: “If You See This, Think This”

Clinical Clue	Think This First	Next Step
Depression + weight gain + cold intolerance + constipation	Hypothyroidism	Check thyroid-stimulating hormone (TSH)
Depression + history of “high” periods with decreased sleep need	Bipolar Disorder	Detailed mood history; avoid antidepressant monotherapy
Depression + snoring + daytime sleepiness + obesity	Obstructive Sleep Apnea	STOP-BANG score; refer for sleep study
Depression + paresthesias + unsteady gait in elderly	Vitamin B12 Deficiency	Check B12, methylmalonic acid; treat even if “low-normal”
Depression + tremor + bradykinesia + rigidity	Parkinson Disease	Neurological examination; neurology referral
Depression starting shortly after new medication	Drug-Induced Depression	Review medication list; trial discontinuation if possible
Depression + heavy alcohol use	Alcohol-Induced Depressive Disorder	Address alcohol use; reassess mood after 4 weeks abstinence
Chronic low-grade depression for years, “always been this way”	Persistent Depressive Disorder (Dysthymia)	Screen for superimposed major depression; long-term treatment plan
Depression + delusions of guilt or nihilism	Major Depression with Psychotic Features	Urgent psychiatric referral; antipsychotic augmentation needed
Depression beginning in fall/winter, resolving in spring	Seasonal Affective Disorder	Light therapy; vitamin D level; consider antidepressant seasonally
Depression + unexplained weight loss + anorexia in older adult	Occult Malignancy	Age-appropriate cancer screening; consider CT imaging
Depression within 4 weeks postpartum	Postpartum Depression	Edinburgh Postnatal Depression Scale; assess for infanticidal ideation; urgent treatment

6. Diagnostic Investigations

A stepwise, cost-effective approach guided by clinical suspicion

Depression is primarily a clinical diagnosis based on history and mental status examination. However, laboratory investigations are essential to rule out medical conditions that can cause or contribute to depressive symptoms. A targeted approach based on clinical presentation is more cost-effective than extensive routine screening.

Baseline Investigations for All Patients with New-Onset Depression

Investigation	Purpose	What to Look For	Practical Points
Thyroid-Stimulating Hormone (TSH)	Screen for thyroid dysfunction	Elevated TSH (hypothyroidism) or suppressed TSH (hyperthyroidism)	Most important single test; subclinical hypothyroidism (TSH 5-10) may still contribute to symptoms; consider free T4 if TSH abnormal
Complete Blood Count (CBC)	Screen for anemia, infection, other hematologic abnormalities	Low hemoglobin (anemia); macrocytosis (B12/folate deficiency, alcohol); leukocytosis or leukopenia	Iron deficiency can cause fatigue even without frank anemia; check ferritin if suspected
Basic Metabolic Panel	Assess electrolytes, renal function, glucose	Hypercalcemia (hyperparathyroidism); hyponatremia; renal impairment; hyperglycemia	Baseline for medication monitoring; diabetes screening; hypercalcemia often missed cause of depression
Vitamin B12	Screen for deficiency (common, treatable)	Level less than 200 pg/mL is deficient; 200-400 pg/mL is borderline	Neuropsychiatric symptoms may occur with “low-normal” levels; if borderline, check methylmalonic acid (elevated confirms deficiency)
Folate	Screen for deficiency	Low red blood cell folate or serum folate	Less specific for deficiency than B12; important if macrocytosis present or alcohol use

Minimum Workup for All Patients: TSH + CBC + Basic Metabolic Panel + B12

This combination screens for the most common and treatable medical causes of depression. Additional investigations should be guided by clinical presentation and risk factors.

Targeted Investigations by Clinical Suspicion

If Suspecting Endocrine Causes

First-Line Tests

Free T4: If TSH abnormal; confirms hypo- or hyperthyroidism
Fasting glucose or HbA1c: If diabetes suspected or risk factors present
Calcium (corrected for albumin): If hypercalcemia suspected; lethargy, confusion, constipation

Second-Line Tests

Morning cortisol: If Cushing syndrome or Addison disease suspected; 8 AM sample
Parathyroid hormone (PTH): If calcium elevated; confirms hyperparathyroidism
Testosterone (in men): If low libido, fatigue, erectile dysfunction; morning sample
DHEA-S, FSH, LH: If hormonal etiology suspected based on clinical picture

If Suspecting Nutritional Deficiencies

First-Line Tests

Vitamin B12: Especially in elderly, vegetarians, metformin users, post-gastric surgery
Folate: If macrocytosis, alcohol use, malnutrition
Ferritin: If fatigue prominent; can be low without anemia

Second-Line Tests

Methylmalonic acid: If B12 borderline (200-400 pg/mL); elevated confirms functional deficiency
Homocysteine: Elevated in B12 and folate deficiency
Vitamin D (25-hydroxyvitamin D): If risk factors (limited sun exposure, dark skin, obesity, northern latitude); target greater than 30 ng/mL
Iron studies (Fe, TIBC, transferrin saturation): If ferritin equivocal or inflammation present

If Suspecting Sleep Apnea

STOP-BANG Screening Questionnaire

Use to screen for obstructive sleep apnea in patients with depression plus suggestive features:

Snoring — Do you snore loudly?
Tired — Do you often feel tired or sleepy during the day?
Observed — Has anyone observed you stop breathing during sleep?
Pressure — Do you have high blood pressure?
BMI — Is BMI greater than 35?
Age — Age greater than 50?
Neck — Neck circumference greater than 40 cm?
Gender — Male gender?

Scoring: 0-2 = low risk; 3-4 = intermediate risk; 5-8 = high risk. Refer for polysomnography if intermediate or high risk.

If Suspecting Neurological Causes

Cognitive Screening

Montreal Cognitive Assessment (MoCA): More sensitive than MMSE for mild cognitive impairment; score less than 26 suggests impairment
Mini-Mental State Examination (MMSE): Widely used; less sensitive for early dementia

Tip: Depression can cause “pseudodementia” with poor test performance that improves with treatment or encouragement.

Imaging and Other Tests

Brain MRI: If focal neurological signs, cognitive decline, late-onset depression, atypical presentation
CT head: If MRI not available; less sensitive for white matter changes
EEG: If seizures suspected; frontal lobe epilepsy can present with mood/behavioral changes
Lumbar puncture: Rarely needed; consider if normal pressure hydrocephalus suspected (gait, incontinence, dementia)

If Suspecting Substance-Related Causes

Substance	Screening Test	Notes
Alcohol	AUDIT-C questionnaire; GGT, MCV (indirect markers); ethyl glucuronide (recent use)	Elevated GGT and MCV suggest chronic heavy use; liver function tests (AST:ALT ratio >2 suggests alcoholic liver)
Cannabis	Urine drug screen (THC); self-report	THC can persist in urine for weeks in chronic users
Opioids	Urine drug screen; prescription monitoring program check	Screen for opioid use disorder; consider referral for medication-assisted treatment
Stimulants	Urine drug screen (amphetamines, cocaine)	Crash and withdrawal cause profound depression; may need to differentiate from primary depression

Standardized Screening and Severity Assessment Tools

Tool	Purpose	Scoring and Interpretation	When to Use
Patient Health Questionnaire-9 (PHQ-9)	Depression screening and severity monitoring	0-4 minimal; 5-9 mild; 10-14 moderate; 15-19 moderately severe; 20-27 severe. Question 9 screens for suicidal ideation.	Initial screening; monitoring treatment response (repeat every 2-4 weeks); score of ≥10 suggests major depression
Patient Health Questionnaire-2 (PHQ-2)	Ultra-brief screening	Score ≥3 is positive screen; follow up with PHQ-9	Rapid screening in busy settings; annual wellness visits
Generalized Anxiety Disorder-7 (GAD-7)	Anxiety screening (commonly comorbid)	0-4 minimal; 5-9 mild; 10-14 moderate; 15-21 severe	Whenever depression suspected; anxiety and depression frequently co-occur
Mood Disorder Questionnaire (MDQ)	Screen for bipolar disorder	Positive screen: ≥7 “yes” items + several occurring together + causing problems	All patients with depression to rule out bipolar; especially if prior antidepressant non-response or adverse reaction
Edinburgh Postnatal Depression Scale (EPDS)	Postpartum depression screening	Score ≥10 suggests possible depression; ≥13 high probability; Question 10 screens for self-harm	All postpartum women; can also be used during pregnancy
Columbia Suicide Severity Rating Scale (C-SSRS)	Structured suicide risk assessment	Categorizes ideation by severity; assesses plan, intent, behavior	When suicidal ideation present; provides structured documentation; guides disposition
Geriatric Depression Scale (GDS-15)	Depression screening in elderly	0-4 normal; 5-8 mild; 9-11 moderate; 12-15 severe	Elderly patients; yes/no format may be easier for cognitively impaired

Empiric Treatment Trials as Diagnostic Tools

When Diagnosis Remains Uncertain

In some cases, response to empiric treatment can help clarify diagnosis:

Thyroid hormone replacement trial: If subclinical hypothyroidism (TSH 5-10 mIU/L) with symptoms; improvement supports treatment continuation
Vitamin B12 supplementation: If borderline B12 with neuropsychiatric symptoms; low risk, may show benefit within 1-2 months
CPAP trial for sleep apnea: If moderate-severe obstructive sleep apnea on sleep study; mood often improves significantly with adherent use
Medication discontinuation trial: If temporal relationship to suspect medication; monitor mood after stopping (when medically safe)
Period of abstinence from alcohol: If heavy alcohol use; reassess depression after 4 weeks of sobriety; primary depression persists, substance-induced depression resolves

Pre-Treatment Baseline Investigations

Before Starting Antidepressant Treatment, Document:

Weight: Baseline for monitoring; some antidepressants cause weight gain
Blood pressure and heart rate: SNRIs can increase blood pressure; TCAs affect cardiac conduction
ECG: If using tricyclic antidepressants, if pre-existing cardiac disease, or if QT-prolonging medications co-prescribed
Liver function tests: Baseline for medications with hepatic metabolism; required for some agents
Renal function: Dose adjustment needed for some medications in renal impairment
Sodium: SSRIs can cause hyponatremia (SIADH), especially in elderly
Pregnancy test: In women of childbearing potential; counsel regarding risks

Investigation Algorithm Summary

Patient Scenario	Minimum Workup	Consider Adding
Typical presentation, no red flags	TSH, CBC, BMP, B12	PHQ-9 for baseline severity; MDQ for bipolar screening
Elderly patient (>65 years)	TSH, CBC, BMP, B12, folate, vitamin D	Cognitive screen (MoCA); consider neuroimaging if cognitive symptoms
Suspected substance use	TSH, CBC, BMP, B12, LFTs	Urine drug screen; GGT; hepatitis panel if IV drug use
Obese patient with fatigue	TSH, CBC, BMP, B12, fasting glucose/HbA1c	Sleep study referral if STOP-BANG positive; lipid panel
Postpartum patient	TSH, CBC, ferritin	EPDS screening; assess for bipolar features
Atypical features or treatment resistance	TSH, CBC, BMP, B12, folate, vitamin D	Morning cortisol; brain MRI; consider specialty referral
Late-onset depression (first episode >50 years)	TSH, CBC, BMP, B12, calcium	Brain MRI (rule out structural lesion, vascular changes); cognitive screen

7. Pattern Recognition and Clinical Decision-Making

Practical algorithms and decision pathways

Step 1: Is This Urgent?

Clinical Scenario	Urgency Level	Immediate Action
Active suicidal ideation with plan and intent	EMERGENT	Do not leave patient alone; emergency psychiatric evaluation; consider involuntary hold if refusing care; remove access to lethal means
Psychotic features (delusions, hallucinations)	EMERGENT	Same-day psychiatric evaluation; antidepressant alone is insufficient; may need hospitalization
Severe functional decline (not eating, not caring for self)	EMERGENT	Assess safety and medical stability; consider hospitalization for stabilization; check electrolytes, renal function
Recent suicide attempt or self-harm	EMERGENT	Emergency department evaluation; medical clearance if needed; psychiatric assessment; safety planning
Passive suicidal ideation without plan	URGENT	Same-day or next-day assessment; safety planning; frequent follow-up; involve support system; consider urgent psychiatry referral
Suspected bipolar disorder presenting as depression	URGENT	Avoid antidepressant monotherapy; psychiatry referral within 1-2 weeks; mood stabilizer may be needed first
Postpartum depression	URGENT	Same-week evaluation; screen for suicidal and infanticidal ideation; assess bonding and infant safety; early intervention critical
Moderate depression with functional impairment	ROUTINE	Initiate treatment within 1-2 weeks; baseline investigations; follow-up in 2-4 weeks; provide crisis resources
Mild depression, adjustment disorder	ROUTINE	Supportive counseling; consider watchful waiting; psychotherapy referral; lifestyle interventions; follow-up in 2-4 weeks

Step 2: Classify by Severity

Mild Depression

PHQ-9: 5-9

Minimal functional impairment; able to work and maintain relationships

Proceed to: Algorithm A (Watchful Waiting/Psychotherapy)

Moderate Depression

PHQ-9: 10-14

Notable functional impairment; difficulty at work or in relationships

Proceed to: Algorithm B (Antidepressant and/or Psychotherapy)

Severe Depression

PHQ-9: 15-27

Significant functional impairment; unable to work; self-care affected

Proceed to: Algorithm C (Antidepressant + Intensified Care)

Step 3: Follow the Appropriate Algorithm

Algorithm A: Mild Depression (PHQ-9: 5-9)

Clinical Scenario	Recommended Approach	Follow-Up
First episode, clear precipitant, good support	Watchful waiting with active monitoring; lifestyle interventions (exercise, sleep hygiene, stress reduction); supportive counseling	2-4 weeks; if not improving, escalate to Algorithm B
Recurrent episode (history of prior depression)	Consider early medication given recurrence; psychotherapy referral; closer monitoring	2 weeks initially; patient preference guides treatment choice
Patient preference for medication	Respect patient preference; start low-dose SSRI; combine with lifestyle measures	2-4 weeks for tolerability; 4-6 weeks for efficacy assessment
Patient preference for psychotherapy only	Refer for cognitive behavioral therapy or interpersonal therapy; structured, time-limited approach	Check in at 4-6 weeks; if not accessing therapy or not improving, reassess

Algorithm B: Moderate Depression (PHQ-9: 10-14)

Clinical Scenario	Recommended Approach	Follow-Up
Typical presentation, no complicating factors	Start SSRI (sertraline, escitalopram first-line); offer psychotherapy; provide psychoeducation	2 weeks for tolerability; 4-6 weeks for efficacy; target 50% reduction in PHQ-9
Prominent anxiety symptoms	SSRI preferred (also treats anxiety); consider SNRI if fatigue prominent; avoid benzodiazepines long-term	GAD-7 monitoring alongside PHQ-9; 2-4 week intervals
Prominent insomnia	Consider mirtazapine or trazodone augmentation for sleep; sleep hygiene education; address separately if persists	Sleep often improves as depression improves; reassess at 4-6 weeks
Prior good response to specific antidepressant	Restart previously effective medication at therapeutic dose	May see faster response to known effective treatment
Family member responded to specific antidepressant	Consider starting with same medication class	Genetic factors influence response; family history can guide selection

Algorithm C: Severe Depression (PHQ-9: 15-27)

Clinical Scenario	Recommended Approach	Follow-Up
Severe depression, no psychotic features, safe at home	Start antidepressant promptly; weekly follow-up initially; psychotherapy if able to engage; involve support system	Weekly for first 4 weeks; phone check-ins between visits; crisis line provided
Severe depression with suicidal ideation	Same-day safety assessment; safety planning; means restriction counseling; consider urgent psychiatry; frequent contact	Within 48-72 hours initially; daily check-ins by phone if high risk
Severe depression with psychotic features	Urgent psychiatry referral; antidepressant plus antipsychotic required; consider hospitalization; ECT may be indicated	Psychiatry-led; daily if inpatient; very close monitoring if outpatient
Severe depression, unable to function or care for self	Consider hospitalization for stabilization; medical evaluation; involve family/caregivers; may need higher level of care	Depends on setting; transition planning if hospitalized
Treatment-resistant (failed 2+ adequate trials)	Psychiatry referral; reassess diagnosis (bipolar?); consider augmentation strategies, ketamine/esketamine, or ECT	Specialist-guided; may need more intensive interventions

“What Do I Do If…” Decision Reference

Clinical Situation	Immediate Action	Next Step
Patient discloses suicidal thoughts	Stay calm; express concern; do not leave patient alone; assess severity (passive vs. active, plan, intent, means)	Complete safety assessment; develop safety plan; determine disposition (home vs. emergency department); provide crisis resources
Positive bipolar screen (MDQ positive)	Hold antidepressant if not yet started; detailed history of manic symptoms	Psychiatry referral; if bipolar confirmed, mood stabilizer first; antidepressant monotherapy contraindicated
TSH abnormal (hypothyroid)	Start thyroid replacement; recheck TSH in 6-8 weeks	Reassess mood after thyroid normalized; may still need antidepressant; often synergistic improvement
Patient refuses medication	Explore concerns (side effects, stigma, prior experience); validate; provide education	Offer psychotherapy; lifestyle interventions; agree on monitoring plan; revisit medication if not improving
No response after 4-6 weeks on antidepressant	Confirm adherence; ensure adequate dose; review diagnosis	Optimize dose to maximum tolerated; if still no response at 8 weeks, switch or augment; consider psychiatry referral
Partial response at 8 weeks	Continue current medication; consider optimization	Augmentation (add bupropion, mirtazapine, or aripiprazole) or switch to different class; add psychotherapy if not already engaged
Intolerable side effects	Assess severity; many side effects improve over 1-2 weeks	If persistent: reduce dose, switch medication, or add adjunct to manage side effect; do not abruptly stop
Patient wants to stop medication (improved)	Counsel on relapse risk; discuss optimal duration (minimum 6-12 months after remission)	If appropriate to discontinue: taper gradually over weeks; monitor for relapse; provide action plan if symptoms return
Elderly patient with new depression	Lower starting doses; watch for drug interactions; cognitive screen	Monitor for hyponatremia (SSRIs); falls risk; consider neuroimaging if atypical features
Pregnant patient with depression	Discuss risks and benefits; untreated depression also has risks	Sertraline generally preferred; close monitoring; coordinate with obstetrics; plan for postpartum

First-Line Antidepressant Selection Guide

Clinical Feature	Consider This Medication	Rationale
Typical depression, no specific features	Sertraline or Escitalopram	Best evidence base; generally well-tolerated; sertraline safest in cardiac disease
Prominent anxiety	Sertraline, Escitalopram, or Paroxetine	SSRIs effective for both depression and anxiety
Fatigue, low energy predominant	Bupropion or SNRI (duloxetine, venlafaxine)	Activating; noradrenergic and/or dopaminergic effects
Insomnia predominant	Mirtazapine	Sedating; also helps appetite; weight gain can be limiting
Chronic pain comorbidity	Duloxetine or Amitriptyline	FDA-approved for pain conditions; addresses both issues
Concern about sexual dysfunction	Bupropion or Mirtazapine	Lower rates of sexual side effects than SSRIs
Concern about weight gain	Bupropion	Weight-neutral or promotes modest weight loss; avoid mirtazapine, paroxetine
Smoking cessation also desired	Bupropion	Also FDA-approved for smoking cessation
Prior good response to specific medication	Same medication	Predictor of future response

Troubleshooting Treatment-Resistant Depression

Before Labeling Depression as “Treatment-Resistant,” Ask:

Is the diagnosis correct? — Reassess for bipolar disorder, anxiety disorder, personality disorder, medical causes, substance use
Was the medication trial adequate? — Adequate dose for adequate duration (typically 6-8 weeks at therapeutic dose)
Is the patient adherent? — Up to 50% of patients do not take medications as prescribed; ask non-judgmentally
Are there perpetuating factors? — Ongoing stressors, untreated comorbidities (anxiety, substance use, chronic pain), poor sleep
Is there a medical contributor? — Recheck thyroid, B12, vitamin D; consider sleep study; review medication list
Would psychotherapy help? — Medication plus psychotherapy more effective than either alone
Is specialist referral indicated? — After 2 adequate trials, consider psychiatry referral for augmentation strategies or alternative treatments

8. Clinical Pearls and Pitfalls

Practical wisdom — learn from successes and avoid common mistakes

Must-Know Clinical Pearls

Always screen for bipolar disorder: Ask every depressed patient about lifetime history of manic or hypomanic episodes. Up to 40% of “treatment-resistant depression” is actually undiagnosed bipolar disorder. Antidepressant monotherapy in bipolar can trigger mania or rapid cycling.

Asking about suicide does not cause suicide: Research consistently shows that asking about suicidal thoughts does not plant the idea or increase risk. Patients are often relieved to discuss these thoughts openly. Always ask directly.

TSH is the most important lab test: Thyroid dysfunction is common, treatable, and can completely explain depressive symptoms. Check TSH in every patient with new depression. Even subclinical hypothyroidism can contribute to mood symptoms.

Give antidepressants time to work: Full therapeutic effect typically takes 4-6 weeks, sometimes up to 8-12 weeks. Inform patients that improvement is gradual. Side effects often diminish while benefits increase over time.

Combine medication with psychotherapy when possible: The combination is more effective than either treatment alone, especially for moderate-to-severe depression. Psychotherapy provides skills that persist after treatment ends.

Sleep apnea is an underdiagnosed cause of depression: Screen obese patients and those with fatigue, snoring, or daytime sleepiness. Treatment with CPAP can significantly improve mood even without antidepressants.

Safety planning is more effective than “no-suicide contracts”: Collaborative safety planning (identifying warning signs, coping strategies, support contacts, means restriction) is evidence-based. Written “contracts” have no evidence of efficacy and may give false reassurance.

Continue treatment long enough to prevent relapse: After remission, continue antidepressants for at least 6-12 months for first episode, longer for recurrent depression. Premature discontinuation is a leading cause of relapse.

Critical Pitfalls to Avoid

Starting antidepressants without screening for bipolar: Antidepressant monotherapy in bipolar disorder can trigger mania, mixed states, or rapid cycling. Always ask about prior “highs” before prescribing.

Stopping antidepressants too soon: Many patients want to stop medication once they feel better. Discontinuation before 6-12 months of remission dramatically increases relapse risk. Educate early and often.

Inadequate dosing or duration before switching: “Treatment failure” often reflects inadequate trials. Ensure therapeutic dose for sufficient duration (6-8 weeks) before concluding a medication does not work.

Prescribing benzodiazepines as primary treatment: Benzodiazepines provide quick relief but do not treat depression, risk dependence, and can worsen depression long-term. Use sparingly and short-term if at all.

Missing medical causes of depression: Not checking TSH, B12, or other basic labs can mean missing a treatable cause. Medical conditions causing depression will not respond to antidepressants alone.

Dismissing elderly depression as “normal aging”: Depression is not a normal part of aging. Elderly patients are at higher suicide risk and often underdiagnosed. Screen actively and treat appropriately.

Not addressing alcohol use: Heavy alcohol use causes and worsens depression. Treating depression without addressing alcohol is often futile. Depression may resolve with abstinence alone.

Abrupt antidepressant discontinuation: Sudden stopping of SSRIs and SNRIs can cause discontinuation syndrome (dizziness, nausea, paresthesias, irritability). Always taper gradually, especially paroxetine and venlafaxine.

Key Takeaways

Low mood is one of the most common presenting complaints in primary care; systematic evaluation prevents missed diagnoses.
Safety assessment (suicidal ideation, psychotic features, functional status) should be performed at every encounter with a depressed patient.
Always screen for bipolar disorder before starting antidepressant therapy — the treatment is fundamentally different.
Medical causes of depression (hypothyroidism, B12 deficiency, sleep apnea) are common and treatable; check basic labs in all new presentations.
Review the medication list for drugs that can cause depression (beta-blockers, corticosteroids, and others); temporal relationship to symptom onset is key.
PHQ-9 is a validated, practical tool for screening, severity assessment, and treatment monitoring — use it systematically.
First-line treatment for moderate-to-severe depression is an SSRI (sertraline or escitalopram), with psychotherapy when available.
Set realistic expectations: antidepressants typically take 4-6 weeks for full effect; side effects often improve while benefits increase.
Combination treatment (medication plus psychotherapy) is more effective than either alone for moderate-to-severe depression.
Continue antidepressants for at least 6-12 months after remission to reduce relapse risk; taper gradually when discontinuing.
Treatment-resistant depression requires reassessment of diagnosis, adherence, comorbidities, and perpetuating factors before escalating treatment.
Refer to psychiatry for psychotic features, bipolar disorder, treatment resistance (after 2 adequate trials), or high suicide risk.

Quick Reference Algorithm

Systematic Approach to Low Mood:

Assess Safety: Screen for suicidal ideation at every visit; determine urgency of evaluation and disposition.
Screen for Bipolar: Ask about lifetime history of manic or hypomanic episodes; use MDQ if uncertain.
Take Comprehensive History: Use “SAD CAGES” mnemonic; characterize duration, severity, and functional impact.
Review Medications and Substances: Identify drugs that cause depression; assess alcohol and substance use.
Order Baseline Investigations: Minimum: TSH, CBC, BMP, B12; add others based on clinical suspicion.
Classify Severity: Use PHQ-9 to categorize as mild (5-9), moderate (10-14), or severe (15-27).
Develop Treatment Plan: Match intensity to severity; involve patient in shared decision-making.
Schedule Follow-Up: Early and frequent follow-up improves outcomes; reassess safety and response at each visit.
Monitor and Adjust: Expect 4-6 weeks for antidepressant effect; optimize dose before switching; consider augmentation for partial response.
Plan for Maintenance: Continue treatment for at least 6-12 months after remission; taper gradually when discontinuing.