Drug Monograph

Duloxetine (Cymbalta)

duloxetine hydrochloride delayed-release capsules

Serotonin-Norepinephrine Reuptake Inhibitor (SNRI)·Oral
Pharmacokinetic Profile
Half-Life
~12 h (range 8–17 h)
Metabolism
CYP1A2 and CYP2D6 (dual pathway)
Protein Binding
>90% (albumin & α1-acid glycoprotein)
Bioavailability
~50% (range 32–80%)
Volume of Distribution
~1,640 L
Clinical Information
Drug Class
SNRI
Available Doses
20, 30, 60 mg delayed-release capsules
Route
Oral, once daily, with or without food
Renal Adjustment
Avoid in severe impairment (GFR <30 mL/min)
Hepatic Adjustment
Avoid in chronic liver disease or cirrhosis
Pregnancy
3rd trimester: neonatal adaptation syndrome; may cause fetal harm (animal data)
Lactation
Excreted in breast milk (animal data)
Schedule
Prescription only (not scheduled)
Generic Available
Yes
Black Box Warning
Suicidal thoughts & behaviours in young adults
Hepatotoxicity
Fatal hepatic failure reported; avoid with alcohol or liver disease
Rx

Indications

IndicationApproved PopulationTherapy TypeStatus
Major Depressive Disorder (MDD)AdultsMonotherapyFDA Approved
Generalized Anxiety Disorder (GAD)Adults & paediatric ≥7 yearsMonotherapyFDA Approved
Diabetic Peripheral Neuropathic Pain (DPNP)AdultsMonotherapyFDA Approved
Fibromyalgia (FM)Adults & paediatric ≥13 yearsMonotherapyFDA Approved
Chronic Musculoskeletal PainAdults (OA & CLBP)MonotherapyFDA Approved

Duloxetine is the most broadly indicated SNRI, with five FDA-approved indications spanning psychiatry, neurology, and pain medicine. Initially approved in 2004 for MDD, its dual serotonin-norepinephrine reuptake inhibition makes it particularly suited to conditions involving comorbid pain and depression. The 60 mg once-daily dose is the therapeutic target across most indications, with no consistent evidence of added benefit above this dose. Duloxetine is one of only two SNRIs (with milnacipran) approved for fibromyalgia, and it is the only SNRI approved specifically for chronic musculoskeletal pain including osteoarthritis and chronic low back pain.

Off-Label Uses

Stress urinary incontinence: Approved outside the US (e.g., UK); failed US approval due to hepatotoxicity and suicidality concerns. Evidence quality: High (multiple RCTs).

Chemotherapy-induced peripheral neuropathy: Evidence quality: Moderate.

OCD (adjunctive or monotherapy): Evidence quality: Low–Moderate.

Dose

Dosing

Adult Dosing by Clinical Scenario

Clinical ScenarioStarting DoseMaintenance DoseMaximum DoseNotes
Major depression40–60 mg/day60 mg once daily120 mg/dayCan start at 20 mg BID or 30 mg BID or 60 mg QD. May start at 30 mg QD for 1 week for tolerability. No evidence >60 mg adds benefit
120 mg effective but no clear advantage over 60 mg
Generalised anxiety — adults <65 y60 mg once daily60 mg once daily120 mg/dayMay start at 30 mg QD for 1 week. If dose increase needed, use 30 mg increments. No evidence >60 mg adds benefit
Generalised anxiety — geriatric30 mg once daily60 mg once daily120 mg/dayStart 30 mg QD for 2 weeks before increasing to 60 mg
Longer lead-in than younger adults
Diabetic neuropathic pain60 mg once daily60 mg once daily60 mg/dayNo evidence higher doses add benefit; higher doses less well tolerated. Consider lower start if tolerability concern
Consider renal function in diabetic patients
Fibromyalgia — adults30 mg once daily60 mg once daily60 mg/dayStart 30 mg for 1 week then increase to 60 mg. No evidence >60 mg helps; higher doses more adverse effects
Chronic musculoskeletal pain (OA/CLBP)30 mg once daily60 mg once daily60 mg/dayStart 30 mg for 1 week then increase to 60 mg. No evidence higher doses add benefit

Paediatric Dosing

Clinical ScenarioStarting DoseMaintenance DoseMaximum DoseNotes
GAD (ages 7–17)30 mg once daily30–60 mg once daily120 mg/dayStart 30 mg for 2 weeks before considering increase to 60 mg. Some may benefit above 60 mg; increase by 30 mg increments
Fibromyalgia (ages 13–17)30 mg once daily30–60 mg once daily60 mg/dayMay increase to 60 mg based on response and tolerability
Critical: Hepatic and Renal Restrictions

Unlike venlafaxine (which allows dose reduction), duloxetine should be avoided entirely in patients with chronic liver disease, cirrhosis, or severe renal impairment (GFR <30 mL/min). In end-stage renal disease, duloxetine Cmax and AUC were approximately 100% higher, and metabolite levels 7–9 fold higher than normal. Also avoid in patients with substantial alcohol use due to hepatotoxicity risk. MAOI washout: 14 days before starting duloxetine; only 5 days after stopping duloxetine (shorter than venlafaxine at 7 days).

PK

Pharmacology

Mechanism of Action

Duloxetine is a potent inhibitor of both serotonin (5-HT) and norepinephrine (NE) reuptake with weak inhibition of dopamine reuptake. Unlike venlafaxine, duloxetine exhibits relatively balanced 5-HT and NE inhibition even at lower doses, rather than becoming predominantly noradrenergic only at higher doses. This balanced dual activity from the outset contributes to its efficacy across both psychiatric and pain indications. Duloxetine does not inhibit monoamine oxidase and has no significant affinity for dopaminergic, adrenergic, cholinergic, histaminergic, opioid, glutamate, or GABA receptors. Notably, duloxetine is a moderate inhibitor of CYP2D6, which distinguishes it from venlafaxine (weak CYP2D6 inhibitor) and creates clinically important interactions with CYP2D6 substrates.

ADME Profile

ParameterValueClinical Implication
AbsorptionWell absorbed; bioavailability ~50% (range 32–80%); Tmax ~6 h; delayed-release enteric coating prevents degradation in acid; food does not affect AUC but delays Tmax by ~6–10 hMust swallow whole — do not crush or chew (acid degrades to naphthol); conditions slowing gastric emptying may affect coating integrity
DistributionVd ~1,640 L; >90% protein-bound (albumin and α1-acid glycoprotein)Very large Vd indicates extensive tissue distribution; high protein binding — potential for displacement interactions with other highly bound drugs not fully studied
MetabolismExtensive hepatic via CYP1A2 and CYP2D6 (dual pathway); metabolites not pharmacologically active; moderate CYP2D6 inhibitor; does not significantly inhibit CYP1A2, CYP2C9, CYP2C19, or CYP3ADual CYP dependence creates vulnerability: CYP1A2 inhibitors (fluvoxamine: 6-fold AUC increase) and CYP2D6 inhibitors (paroxetine: AUC +60%) both raise levels; smokers (CYP1A2 inducers) have ~1/3 lower exposure; avoid potent CYP1A2 inhibitors
Eliminationt½ ~12 h (range 8–17 h); primarily renal excretion (~70% as metabolites, <1% unchanged); ~20% faecal; elderly females: AUC ~25% higher, t½ ~4 h longer; ESRD: Cmax and AUC ~100% higher, metabolites 7–9×Moderate t½ supports once-daily dosing; significant accumulation in ESRD — avoid use; hepatic impairment markedly increases exposure (5-fold in cirrhosis) — contraindicated
SE

Side Effects

≥10%Very Common (Pooled Adult Data)
Adverse EffectIncidenceClinical Note
NauseaUp to 30% (dose-dependent; 14% at 20 mg, 22% at 60 mg QD)Most common AE across all indications; usually improves in 1–2 weeks; main driver of early discontinuation
HeadacheUp to 18%Similar across indications; usually transient
SomnolenceUp to 21% (dose-dependent; 7% at 20 mg, 15% at 60 mg QD)Includes hypersomnia and sedation; caution with driving
DizzinessUp to 17% (dose-dependent; 6% at 20 mg, 14% at 60 mg QD)Usually transient; related to orthostatic effects
Dry mouthUp to 15%More common in MDD/GAD vs pain populations; encourage oral hygiene
ConstipationUp to 15%Noradrenergic effect; manage with fibre and fluids
1–10%Common
Adverse EffectIncidenceClinical Note
Decreased appetiteUp to 10%May lead to weight loss; monitor especially in paediatric patients
FatigueUp to 10%More common in fibromyalgia and pain trials
InsomniaUp to 10%Consider morning dosing
HyperhidrosisUp to 7%Noradrenergic effect; includes night sweats; may persist
DiarrhoeaUp to 7%Usually mild; serotonergic GI effect
Abdominal painUp to 6%Includes upper and lower; monitor for hepatotoxicity
VomitingUp to 5%Usually early and transient
TremorUp to 5%Fine postural tremor
Erectile dysfunction (males)Up to 5%Enquire proactively; dose-related
Ejaculatory dysfunction (males)Up to 5%Includes delayed ejaculation and ejaculation failure
Decreased libidoUp to 4%Both sexes; likely underreported
SeriousSerious Adverse Effects
Adverse EffectEstimated FrequencyTypical OnsetRequired Action
Hepatotoxicity (including fatal hepatic failure)ALT >3× ULN: 1.25% vs 0.45% placebo; fatal cases reportedMedian ~2 months; can occur any timeDiscontinue for jaundice or significant liver dysfunction; do not resume unless alternative cause identified. Avoid in liver disease/substantial alcohol use
Orthostatic hypotension, falls, syncopeFalls higher rate than placebo; fractures and hospitalisations reportedOften first week; can occur after dose increasesDose reduction or discontinuation; particular concern in elderly; risk increases >60 mg and with concomitant antihypertensives or CYP1A2 inhibitors
Suicidal thoughts/behaviours14 per 1,000 (<18 y); 5 per 1,000 (18–24 y)First weeks to monthsClose monitoring at initiation and dose changes
SJS / erythema multiformeReporting rate exceeds background incidence (1–2 per million person-years)Days to weeksDiscontinue at first sign of blisters, peeling rash, or mucosal erosions
Serotonin syndromeRareHours to daysDiscontinue all serotonergic agents; supportive care
Mania/hypomaniaMDD: 0.1% (4/3,779); none in GAD, DPNP, FM, pain trialsDays to weeksDiscontinue; psychiatric reassessment
Seizures0.02% (3/12,722) vs 0.01% placeboAny time; also reported on discontinuationUse cautiously in seizure disorders
Hyponatraemia (SIADH)Uncommon; Na <110 mmol/L reportedDays to weeks; elderly at higher riskCheck sodium; discontinue; medical management
DiscontinuationDiscontinuation Rates by Indication
MDD
8.4% vs 4.6% placebo
Nausea only AE meeting drug-related criteria (1.1% vs 0.4%)
Pain Indications (DPNP / FM / OA / CLBP)
12.9–17.5% vs 5.1–10.1% placebo
Nausea (2–3.5%), dizziness (1.2%), somnolence (1–1.1%), fatigue (1.1%) across pain trials
Discontinuation Syndrome

Following abrupt or tapered discontinuation, the following symptoms occurred at ≥1% and significantly higher than placebo: dizziness, headache, nausea, diarrhoea, paresthesia, irritability, vomiting, insomnia, anxiety, hyperhidrosis, and fatigue. Gradual dose reduction is recommended. Seizures upon treatment discontinuation have been reported in postmarketing.

Glycaemic Effects in Diabetic Patients

In DPNP trials (mean baseline HbA1c 7.8%), duloxetine was associated with a mean fasting glucose increase of 12 mg/dL and HbA1c increase of 0.5% during extension phases (up to 52 weeks), compared with decreases in routine care groups. Monitor glycaemic control in diabetic patients on duloxetine.

Int

Drug Interactions

Duloxetine is metabolised by both CYP1A2 and CYP2D6, creating dual vulnerability to inhibitors of either pathway. It is itself a moderate CYP2D6 inhibitor, which creates important interactions with narrow-therapeutic-index CYP2D6 substrates. When both CYP1A2 and CYP2D6 are simultaneously inhibited (or a CYP1A2 inhibitor is given to a CYP2D6 poor metaboliser), duloxetine levels can increase 6-fold. Potent CYP1A2 inhibitors should be avoided. Smoking (CYP1A2 induction) reduces duloxetine exposure by approximately one-third.

MajorFluvoxamine (potent CYP1A2 inhibitor)
MechanismPotent CYP1A2 inhibition; duloxetine AUC increased ~6-fold, Cmax ~2.5-fold, t½ ~3-fold
EffectMarkedly elevated duloxetine exposure with high risk of toxicity
ManagementAvoid co-administration. Ciprofloxacin and enoxacin expected to have similar effects
FDA PI
MajorMAOIs (linezolid, IV methylene blue)
MechanismDual serotonergic and noradrenergic enhancement
EffectSerotonin syndrome (potentially fatal)
ManagementContraindicated. 14 days before starting duloxetine; 5 days after stopping before starting MAOI
FDA PI
MajorThioridazine
MechanismDuloxetine’s moderate CYP2D6 inhibition increases thioridazine levels
EffectQT prolongation, ventricular arrhythmias, sudden death risk
ManagementShould not be co-administered
FDA PI
MajorAlcohol (heavy use)
MechanismAdditive hepatotoxicity
EffectSevere liver injury, including fatal hepatic failure
ManagementAvoid prescribing to patients with substantial alcohol use
FDA PI
ModerateCYP2D6 inhibitors (paroxetine, fluoxetine, quinidine)
MechanismCYP2D6 inhibition; paroxetine increased duloxetine AUC ~60%
EffectHigher duloxetine concentrations; greater in CYP2D6 PM patients
ManagementUse with caution; monitor for adverse effects
FDA PI
ModerateCYP2D6 substrates with narrow TI (TCAs, flecainide, propafenone)
MechanismDuloxetine is a moderate CYP2D6 inhibitor; increases levels of these substrates
EffectTCA toxicity (QT prolongation, seizures); antiarrhythmic toxicity
ManagementMonitor TCA levels; reduce TCA dose; approach with caution
FDA PI
ModerateNSAIDs / Aspirin / Warfarin / Anticoagulants
MechanismSNRI-mediated platelet serotonin depletion; additive bleeding risk
EffectIncreased bleeding risk; postpartum haemorrhage reported
ManagementMonitor; warfarin INR not significantly changed in study (n=15) but clinical caution recommended
FDA PI
MinorSmoking / Tobacco
MechanismCYP1A2 induction by polycyclic aromatic hydrocarbons; duloxetine bioavailability reduced by ~1/3
EffectLower duloxetine levels in smokers
ManagementMay need higher doses in smokers; dose reduction if patient stops smoking
FDA PI
Mon

Monitoring

  • Liver FunctionBaseline; repeat if symptoms develop
    Routine
    Hepatic failure (sometimes fatal) reported. ALT >3× ULN in 1.25% vs 0.45% placebo. Median onset ~2 months. Discontinue for jaundice or significant liver dysfunction
  • Blood PressureBaseline, then periodically
    Routine
    Mean increase 0.5 mmHg systolic, 0.8 mmHg diastolic (small but clinically relevant in at-risk patients); larger increases at supratherapeutic doses
  • Mood & SuicidalityWeekly for 4 weeks, biweekly for 8 weeks, then per judgement
    Routine
    Especially in patients <25 years; monitor at dose changes
  • Glycaemic ControlBaseline, then every 3–6 months in diabetic patients
    Routine
    DPNP trials: FBG +12 mg/dL, HbA1c +0.5% over 52 weeks vs routine care. Monitor fasting glucose and HbA1c
  • Falls / OrthostasisAt initiation, dose changes, and in elderly
    Trigger-based
    Higher fall rate than placebo. Falls with fractures and hospitalisations reported. Risk higher with antihypertensives, CYP1A2 inhibitors, doses >60 mg, and elderly
  • Sodium (Na+)Baseline in at-risk; recheck 2–4 weeks
    Trigger-based
    Na <110 mmol/L reported. Elderly, diuretic users at higher risk
  • Sexual FunctionBaseline, then each visit
    Routine
    Enquire proactively per FDA PI; rates likely underestimated
  • Urinary SymptomsIf symptoms develop
    Trigger-based
    Urinary hesitation and retention reported postmarketing; some cases required catheterisation/hospitalisation
CI

Contraindications & Cautions

Absolute Contraindications

  • Concurrent MAOI use or within 14 days of stopping MAOI / within 5 days of stopping duloxetine (linezolid, IV methylene blue included)
  • Chronic liver disease or cirrhosis — markedly increased exposure; fatal hepatic failure reported
  • Severe renal impairment (GFR <30 mL/min) or end-stage renal disease — Cmax/AUC doubled, metabolites 7–9× higher
  • Substantial alcohol use — additive hepatotoxicity risk

Relative Contraindications (Specialist Input Recommended)

  • Concurrent potent CYP1A2 inhibitors (fluvoxamine, ciprofloxacin, enoxacin) — should be avoided; 6-fold AUC increase
  • Concurrent thioridazine — should not be co-administered; QT prolongation risk via CYP2D6 inhibition
  • Undiagnosed bipolar disorder — mania risk 0.1% in MDD trials

Use with Caution

  • Elderly patients — higher fall risk, orthostatic hypotension risk, hyponatraemia risk; AUC 25% higher in elderly females
  • Conditions slowing gastric emptying (e.g., diabetic gastroparesis) — may affect enteric coating integrity
  • Seizure disorders — seizures in 0.02% (3/12,722); not systematically evaluated in epilepsy
  • Anatomically narrow angles — angle-closure glaucoma risk
  • Late pregnancy — neonatal adaptation syndrome; postpartum haemorrhage risk
  • Smokers — ~1/3 lower duloxetine exposure; may need higher doses; stopping smoking requires dose reduction
  • Concurrent CYP2D6 substrates with narrow TI — duloxetine is a moderate CYP2D6 inhibitor
FDA Boxed Warning Suicidal Thoughts and Behaviours

Antidepressants increased the risk of suicidal thinking and behaviour in children, adolescents, and young adults (ages 18–24) in short-term studies. No suicides occurred in paediatric duloxetine trials. All patients started on antidepressant therapy should be closely monitored for clinical worsening and emergence of suicidal thoughts, especially during initial months and at dose changes. Families and caregivers should be advised of the need for daily observation.

Pt

Patient Counselling

Purpose of Therapy

Duloxetine works by increasing both serotonin and norepinephrine in the brain. It is used to treat depression, anxiety, nerve pain from diabetes, fibromyalgia, and chronic musculoskeletal pain. Full benefit for mood symptoms may take 2–4 weeks; pain benefits may appear within 1–2 weeks.

How to Take

Swallow capsules whole with water. Do not crush, chew, or open the capsule — the special coating protects the medicine from stomach acid. Take at approximately the same time each day. If you miss a dose, take it as soon as you remember unless it is almost time for the next dose.

Liver Safety
Tell patientDuloxetine can rarely cause liver problems. Avoid heavy alcohol use while taking this medication. Report any yellowing of skin or eyes, dark urine, unexplained nausea, or right-sided abdominal pain.
Call prescriberImmediately if jaundice, persistent abdominal pain, or dark urine develops.
Nausea
Tell patientNausea is the most common side effect and usually improves within 1–2 weeks. Taking the medication with food may help. Your prescriber may start with a lower dose to reduce nausea.
Call prescriberIf nausea is severe, lasts beyond 2 weeks, or prevents adequate fluid intake.
Dizziness & Falls
Tell patientDuloxetine can cause dizziness and drops in blood pressure when standing, especially in the first week. Rise slowly from sitting or lying positions. This risk is higher in elderly patients and those taking blood pressure medications.
Call prescriberIf you experience fainting, repeated dizziness, or a fall.
Do Not Stop Suddenly
Tell patientStopping duloxetine abruptly can cause withdrawal symptoms including dizziness, nausea, headache, tingling, and irritability. Always taper gradually under medical supervision.
Call prescriberIf you miss doses or experience withdrawal symptoms during a planned taper.
Blood Sugar (Diabetic Patients)
Tell patientDuloxetine may slightly worsen blood sugar control. Continue monitoring your blood sugar as directed and keep all diabetes appointments.
Call prescriberIf blood sugar readings are consistently higher than usual.
Mood Changes & Suicidality
Tell patientRarely, antidepressants may worsen mood or cause new thoughts of self-harm, especially in the first weeks. Have a trusted person watch for mood changes.
Call prescriberImmediately if new suicidal thoughts, agitation, or unusual behaviour. Go to the emergency department if in immediate danger.
Ref

Sources

Regulatory (PI / SmPC)
  1. CYMBALTA (duloxetine delayed-release capsules). Full Prescribing Information. Eli Lilly and Company. Revised July 2021. FDA LabelPrimary regulatory source for all dosing, adverse reaction data, contraindications, hepatotoxicity warnings, and pharmacokinetics.
  2. CYMBALTA (duloxetine) Summary of Product Characteristics. Electronic Medicines Compendium (eMC). eMCEuropean regulatory source cross-referenced for stress urinary incontinence indication and additional PK data.
Key Clinical Trials
  1. Detke MJ, Lu Y, Goldstein DJ, et al. Duloxetine, 60 mg once daily, for major depressive disorder: a randomized double-blind placebo-controlled trial. J Clin Psychiatry. 2002;63(4):308–315. DOIPivotal MDD trial establishing efficacy of 60 mg once-daily dosing.
  2. Goldstein DJ, Lu Y, Detke MJ, et al. Duloxetine vs. placebo in patients with painful diabetic neuropathy. Pain. 2005;116(1–2):109–118. DOIKey DPNP trial demonstrating significant pain reduction at 60 mg/day.
  3. Arnold LM, Lu Y, Crofford LJ, et al. A double-blind, multicenter trial comparing duloxetine with placebo in the treatment of fibromyalgia patients with or without major depressive disorder. Arthritis Rheum. 2004;50(9):2974–2984. DOIPivotal fibromyalgia trial demonstrating efficacy independent of comorbid depression.
  4. Rynn M, Russell J, Erickson J, et al. Efficacy and safety of duloxetine in the treatment of generalized anxiety disorder: a flexible-dose, progressive-titration, placebo-controlled trial. Depress Anxiety. 2008;25(3):182–189. DOIFlexible-dose GAD trial supporting the 60–120 mg dosing range.
Guidelines
  1. Lam RW, Kennedy SH, Adams C, et al. CANMAT 2023 update on clinical guidelines for management of MDD in adults. Can J Psychiatry. 2024;69(9):641–687. DOICurrent guideline recommending duloxetine as first-line for MDD, especially with comorbid pain.
  2. Bril V, England J, Franklin GM, et al. Evidence-based guideline: Treatment of painful diabetic neuropathy. Neurology. 2011;76(20):1758–1765. DOIAAN guideline with Level B recommendation for duloxetine 60–120 mg/day in DPNP.
  3. Macfarlane GJ, Kronisch C, Dean LE, et al. EULAR revised recommendations for the management of fibromyalgia. Ann Rheum Dis. 2017;76(2):318–328. DOIEULAR guideline recommending duloxetine for fibromyalgia pain management.
Mechanistic / Basic Science
  1. Bymaster FP, Dreshfield-Ahmad LJ, Threlkeld PG, et al. Comparative affinity of duloxetine and venlafaxine for serotonin and norepinephrine transporters in vitro and in vivo, human serotonin receptor subtypes, and other neuronal receptors. Neuropsychopharmacology. 2001;25(6):871–880. DOIKey pharmacology comparison demonstrating duloxetine’s more balanced 5-HT/NE reuptake inhibition vs venlafaxine.
  2. Gahimer J, Wernicke J, Yalcin I, et al. A retrospective pooled analysis of duloxetine safety in 23,983 subjects. Curr Med Res Opin. 2007;23(1):175–184. DOILarge pooled safety analysis providing hepatotoxicity incidence and overall tolerability data.
Pharmacokinetics / Special Populations
  1. Lobo ED, Bergstrom RF, Reddy S, et al. In vitro and in vivo evaluations of cytochrome P450 1A2 interactions with duloxetine. Clin Pharmacokinet. 2008;47(3):191–202. DOICharacterises the fluvoxamine–duloxetine interaction (6-fold AUC increase) and CYP1A2 pathway contribution.
  2. Skinner MH, Kuan H-Y, Pan A, et al. Duloxetine is both an inhibitor and a substrate of cytochrome P4502D6 in healthy volunteers. Clin Pharmacol Ther. 2003;73(3):170–177. DOIEstablishes duloxetine as a moderate CYP2D6 inhibitor and characterises paroxetine interaction.
  3. Lantz RJ, Gillespie TA, Rash TJ, et al. Metabolism, excretion, and pharmacokinetics of duloxetine in healthy human subjects. Drug Metab Dispos. 2003;31(9):1142–1150. DOIPrimary PK characterisation in humans defining t½, Vd, protein binding, and metabolic pathways.