Drug Monograph
Chlorpromazine
Thorazine · Largactil
Pharmacokinetic Profile
Half-Life
23–37 h (parent drug)
Metabolism
Hepatic via CYP2D6 (primary) and CYP1A2; also CYP3A4 substrate; >10 metabolites
Protein Binding
92–97%
Bioavailability
~20–32% (oral); IM absorption ~10× higher
Volume of Distribution
~21 L/kg
Clinical Information
Drug Class
Low-potency first-generation (typical) antipsychotic
Available Doses
Tabs: 10, 25, 50, 100, 200 mg; IM/IV injection: 25 mg/mL
Route
Oral, IM, IV (IV restricted to severe hiccups, surgery, tetanus)
Renal Adjustment
No specific adjustment required
Hepatic Adjustment
Use with caution; increased bioavailability and delayed elimination in hepatic impairment
Pregnancy
Risk of neonatal EPS/withdrawal with 3rd-trimester use
Lactation
Excreted in breast milk; not recommended
Schedule
Not a controlled substance
Generic Available
Yes (Thorazine brand discontinued in US)
Black Box Warning
Yes — Elderly dementia mortality
Indications for Chlorpromazine
| Indication | Approved Population | Therapy Type | Status |
|---|---|---|---|
| Schizophrenia | Adults and adolescents | Monotherapy | FDA Approved |
| Manic phase of bipolar disorder | Adults | Monotherapy or adjunctive | FDA Approved |
| Nausea and vomiting | Adults and children ≥6 months | Monotherapy | FDA Approved |
| Intractable hiccups | Adults | Monotherapy | FDA Approved |
| Preoperative apprehension | Adults | Adjunctive | FDA Approved |
| Acute intermittent porphyria | Adults | Monotherapy | FDA Approved |
| Tetanus (adjunct) | Adults and children | Adjunctive (with barbiturates) | FDA Approved |
| Severe behavioural problems in children | Children 1–12 years | Monotherapy (after non-antipsychotic failure) | FDA Approved |
Chlorpromazine holds a unique position in psychopharmacology as the first antipsychotic drug, introduced in 1952, and the agent that launched the modern era of psychiatric pharmacotherapy. Although it has been largely supplanted by second-generation antipsychotics for schizophrenia and bipolar disorder, chlorpromazine retains the broadest FDA indication set of any antipsychotic. It remains clinically relevant for intractable hiccups, acute intermittent porphyria, and nausea management in settings where newer antiemetics are unavailable or contraindicated.
Off-Label Uses
Acute agitation and delirium (evidence quality: moderate): Chlorpromazine is sometimes used for acute psychomotor agitation when parenteral access is available, though haloperidol is generally preferred for its lower sedative and hypotensive burden.
Migraine (evidence quality: moderate): IV chlorpromazine at 0.1 mg/kg (max 25 mg) has been studied for acute migraine in emergency settings.
Dosing for Chlorpromazine
Psychiatric Indications — Adults
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Schizophrenia — outpatient, moderate symptoms | 25–75 mg/day PO in 2–3 divided doses | 200–600 mg/day | 800 mg/day PO | 500 mg/day is generally sufficient; little gain above 1000 mg/day Increase gradually over days to weeks |
| Schizophrenia or mania — severe, inpatient | 25 mg IM; then 25–50 mg IM q1–4h PRN | 300–800 mg/day (switch to PO ASAP) | 400 mg IM q4–6h (IM); 2000 mg/day (oral, rare) | Reserve IM for bedfast or acute ambulatory patients; keep patient supine ≥30 min post-injection Gradual increase up to 2000 mg/day may be needed; rarely justified long-term |
| Manic episode of bipolar disorder | 25–50 mg PO TID | 200–600 mg/day | 800 mg/day | Often used short-term until mood stabiliser reaches therapeutic level |
Non-Psychiatric Indications — Adults
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Nausea and vomiting | 10–25 mg PO q4–6h PRN | Same; increase if needed | 25–50 mg IM/IV q4–6h if oral not tolerated | Antiemetic effect mediated by CTZ D2 blockade |
| Intractable hiccups | 25–50 mg PO TID–QID | Same; if persists 2–3 days, switch to IM 25–50 mg TID–QID | 25–50 mg slow IV in 500–1000 mL saline (if IM fails) | Only FDA-approved drug for intractable hiccups; monitor BP closely during IV Oral → IM → IV stepwise approach |
| Acute intermittent porphyria | 25–50 mg PO TID–QID | Same; can usually stop after several weeks | 25–50 mg IM TID–QID (if unable to take PO) | Some patients require maintenance therapy |
| Preoperative apprehension | 25–50 mg PO or 12.5–25 mg IM, 2–3 h before surgery | Single pre-procedure dose | Reduces anxiety and potentiates anaesthetics | |
| Tetanus (adjunct) | 25–50 mg IM TID–QID | Same; IV 25–50 mg diluted to ≥1 mg/mL at 1 mg/min | Determined by clinical response | Given with barbiturates; start low and increase as needed |
Paediatric Dosing
| Clinical Scenario | Starting Dose | Maintenance Dose | Maximum Dose | Notes |
|---|---|---|---|---|
| Severe behavioural problems / Psychosis — outpatient (≥6 mo) | 0.55 mg/kg PO/IM q4–6h PRN | 50–100 mg/day | ≤40 mg/day (≤23 kg); ≤75 mg/day (23–45 kg); 200 mg/day (older hospitalised) | Generally not used under 6 months except where lifesaving Reserve for failure of non-antipsychotic therapies |
| Nausea/vomiting — children (≥6 mo) | 0.55 mg/kg PO/IM q4–6h PRN | Same; per weight limits above | Avoid in Reye syndrome or suspected encephalopathy | |
| Tetanus — children | 0.55 mg/kg IM/IV q6–8h | Max 40 mg/day (≤23 kg); 75 mg/day (23–45 kg) | IV diluted to ≥1 mg/mL at 1 mg/2 min | |
Clinical Pearl: Dose Equivalence
Chlorpromazine 100 mg is the traditional “chlorpromazine equivalent” unit used in psychopharmacology to compare antipsychotic potency. This corresponds to approximately haloperidol 2 mg, risperidone 2 mg, or olanzapine 5 mg. The chlorpromazine equivalent concept is used primarily in research and is a rough clinical guide rather than a precise conversion tool.
Pharmacology of Chlorpromazine
Mechanism of Action
Chlorpromazine is a low-potency phenothiazine antipsychotic that exerts its effects through antagonism at multiple receptor systems. It blocks dopamine D2 receptors in the mesolimbic and mesocortical pathways, producing its antipsychotic effect. Unlike high-potency FGAs such as haloperidol, chlorpromazine also has strong antagonist activity at histamine H1 receptors (causing prominent sedation and weight gain) and alpha-1 adrenergic receptors (causing orthostatic hypotension), along with moderate muscarinic cholinergic receptor blockade (causing anticholinergic side effects such as dry mouth, constipation, and urinary retention). It also possesses moderate serotonergic antagonism. This broad receptor profile results in a different adverse-effect pattern from high-potency agents: more sedation, hypotension, and anticholinergic effects, but less extrapyramidal symptoms at equivalent antipsychotic doses.
ADME Profile
| Parameter | Value | Clinical Implication |
|---|---|---|
| Absorption | Oral bioavailability 20–32% due to extensive first-pass metabolism; Tmax 2–4 h (oral), 15–30 min (IM); IM bioavailability approximately 10-fold higher than oral | Erratic oral absorption with large interindividual variability; IM route provides much more reliable drug exposure for acute situations |
| Distribution | Vd ~21 L/kg; protein binding 92–97%; highly lipophilic; accumulates in body fat; crosses placenta and into breast milk | Extensive tissue distribution with slow release from fat stores; metabolites detectable for up to 18 months after chronic therapy discontinuation |
| Metabolism | Extensive hepatic metabolism via CYP2D6 (primary) and CYP1A2; CYP3A4 substrate; produces >10 metabolites including active 7-hydroxychlorpromazine and norchlorpromazine; moderate CYP2D6 inhibitor; <1% excreted unchanged in urine | May induce its own metabolism (hepatic microsomal enzyme induction), leading to decreasing plasma levels at fixed doses over time; CYP2D6 poor metabolisers at risk for higher levels |
| Elimination | t½ 23–37 h (parent drug); active metabolite t½ 10–40 h; excreted via urine (~50%) and faeces (~50%) as metabolites; not dialysable | Longer half-life supports twice-daily dosing in many patients; children eliminate faster than adults; therapeutic plasma level 100–300 ng/mL |
Side Effects of Chlorpromazine
≥10%Very Common
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| Sedation / Drowsiness | 30–50% | Most prominent side effect of chlorpromazine; usually worse during first 1–2 weeks and may attenuate; dose-related; much higher than high-potency FGAs |
| Orthostatic hypotension | 20–30% | Alpha-1 blockade; particularly after IM injection or during dose titration; keep supine ≥30 min after injection; risk of falls especially in elderly |
| Dry mouth | 15–25% | Anticholinergic effect; increases dental caries risk with chronic use; sugarless gum or saliva substitutes for management |
| Constipation | 10–20% | Anticholinergic effect; can progress to paralytic ileus in severe cases; ensure adequate fibre and fluid intake |
1–10%Common
| Adverse Effect | Incidence | Clinical Note |
|---|---|---|
| EPS (parkinsonism, akathisia, dystonia) | 5–15% | Lower than high-potency FGAs (haloperidol 20–40%); dose-related; manage with dose reduction or anticholinergics |
| Weight gain | 5–15% | H1 receptor antagonism; clinically significant and often progressive; more than haloperidol, comparable to some SGAs |
| Blurred vision | 5–10% | Anticholinergic mydriasis; use with caution in narrow-angle glaucoma |
| Urinary retention | 3–8% | Anticholinergic effect; more problematic in elderly men with BPH |
| Photosensitivity | 3–5% | Phototoxic and photoallergic reactions; counsel on sun protection (SPF ≥30); avoid prolonged sun exposure |
| Nasal congestion | 2–5% | Alpha-adrenergic blockade causing vascular congestion of nasal mucosa |
| Tachycardia | 2–5% | Reflex sympathetic activation from orthostatic hypotension |
SeriousSerious (Regardless of Frequency)
| Adverse Effect | Estimated Frequency | Typical Onset | Required Action |
|---|---|---|---|
| Cholestatic jaundice | ~2% (historical) | Weeks 2–4 of therapy | Discontinue chlorpromazine; usually reversible; chronic jaundice rarely reported; do not rechallenge with any phenothiazine |
| Tardive dyskinesia | ~3–5% per year | Months to years; cumulative risk | Consider discontinuation or switch to SGA; VMAT2 inhibitors for persistent TD; risk highest in elderly women |
| Neuroleptic malignant syndrome | Rare (~0.01–0.02%) | Days to weeks after initiation or dose increase | Immediate discontinuation; ICU-level care; dantrolene or bromocriptine may be considered |
| Agranulocytosis | Rare | Weeks 4–10 of therapy | Urgent CBC; discontinue if confirmed; start antibiotics; monitor until recovery |
| QTc prolongation / Sudden death | Very rare (dose-related) | Any time | Baseline ECG; avoid in patients with known QT prolongation or concurrent QT-prolonging drugs; correct electrolytes |
| Ocular deposits (corneal / lenticular) | Uncommon; increases with cumulative dose | Months to years of chronic use | Annual ophthalmologic exam for chronic use; dose-related; usually does not affect vision unless severe |
| Skin pigmentation (slate-grey) | Uncommon; dose- and duration-related | Years of chronic high-dose use | May be partially reversible on discontinuation; sun-exposed areas most affected |
DiscontinuationDiscontinuation Considerations
Withdrawal Syndrome
Cholinergic rebound
Abrupt withdrawal after chronic use may cause nausea, vomiting, gastritis, dizziness, and tremulousness. Taper gradually or continue anticholinergic agents for several weeks.
Psychotic Relapse
Risk increases within weeks
Cross-taper to an alternative antipsychotic when switching; abrupt cessation in schizophrenia may unmask or worsen TD and precipitate relapse.
Managing Orthostatic Hypotension
Orthostatic hypotension is the most functionally limiting side effect for many patients on chlorpromazine. Advise patients to rise slowly from sitting or lying positions. Ensure adequate hydration. After IM injection, keep the patient supine for at least 30 minutes and monitor blood pressure before ambulation. If a vasopressor is needed, use norepinephrine or phenylephrine only. Do not use epinephrine, as chlorpromazine’s alpha-1 blockade may produce paradoxical further lowering of blood pressure.
Drug Interactions with Chlorpromazine
Chlorpromazine is metabolised primarily by CYP2D6 and CYP1A2, and is itself a moderate CYP2D6 inhibitor. Its pronounced alpha-1 blockade and anticholinergic activity create multiple pharmacodynamic interactions. The broad receptor pharmacology of chlorpromazine makes interaction screening essential, particularly for CNS depressants, QT-prolonging agents, and anticholinergic drugs.
MajorCNS Depressants / Opioids / Alcohol
MechanismAdditive CNS and respiratory depression
EffectProfound sedation, respiratory depression, hypotension; chlorpromazine prolongs and intensifies action of barbiturates and narcotics
ManagementReduce dose of CNS depressant by 1/4 to 1/2 when adding chlorpromazine; avoid alcohol
FDA PIMajorQTc-Prolonging Agents
MechanismAdditive QTc prolongation
EffectIncreased risk of torsades de pointes; chlorpromazine itself causes dose-dependent QT prolongation
ManagementAvoid co-prescription when possible; obtain baseline ECG; correct electrolytes
FDA PIModerateCYP2D6 Inhibitors (fluoxetine, paroxetine, bupropion)
MechanismDecreased chlorpromazine metabolism; increased plasma levels
EffectIncreased sedation, hypotension, and anticholinergic burden
ManagementConsider dose reduction of chlorpromazine; monitor for adverse effects
LexicompModeratePropranolol
MechanismMutual inhibition of hepatic metabolism
EffectIncreased plasma levels of both drugs; additive hypotension
ManagementMonitor blood pressure and heart rate closely; consider dose reduction
FDA PIModerateLithium
MechanismUnknown; rare encephalopathic syndrome
EffectWeakness, lethargy, fever, confusion, EPS, elevated enzymes; irreversible brain damage reported in rare cases
ManagementMonitor closely for early neurological toxicity; discontinue promptly if signs appear
FDA PIModerateEpinephrine (as vasopressor)
MechanismAlpha-1 blockade leaves beta-2 vasodilation unopposed
EffectParadoxical worsening of hypotension
ManagementUse norepinephrine or phenylephrine instead
FDA PIModeratePhenytoin
MechanismChlorpromazine may interfere with phenytoin metabolism
EffectPhenytoin toxicity; chlorpromazine also lowers seizure threshold
ManagementMonitor phenytoin levels; do not reduce anticonvulsant doses when starting chlorpromazine
FDA PIMinorOral Anticoagulants
MechanismChlorpromazine diminishes effect of oral anticoagulants
EffectReduced anticoagulant efficacy
ManagementMonitor INR when initiating or discontinuing chlorpromazine
FDA PIMonitoring for Chlorpromazine
- Blood PressureEach visit; orthostatic during initiation
RoutineOrthostatic hypotension is among the most functionally limiting effects. Measure supine and standing BP during titration and in elderly patients. - ECG (QTc)Baseline; as clinically indicated
RoutineChlorpromazine can prolong QTc. Assess at baseline especially if cardiac risk factors, concurrent QT-prolonging drugs, or high-dose therapy. - Liver Function TestsBaseline; if symptoms arise
Trigger-basedCholestatic jaundice typically occurs weeks 2–4. If fever with grippe-like symptoms occurs, check LFTs. Discontinue if abnormality confirmed. - CBCBaseline; during first few months; if infection symptoms
Trigger-basedAgranulocytosis rare but potentially fatal; most cases weeks 4–10. Warn patients to report sore throat, fever, malaise. Discontinue if ANC <1000/mm3. - EPS AssessmentEach visit; AIMS q6–12 mo
RoutineLower EPS risk than haloperidol but still relevant. Screen for TD using AIMS at least annually; every 3–6 months in elderly. - Metabolic PanelBaseline, 12 wk, then annually
RoutineFasting glucose, HbA1c, lipids. Chlorpromazine can elevate glucose and cholesterol. Weight monitoring monthly for 3 months, then quarterly. - Ophthalmologic ExamAnnually if chronic high-dose use
Trigger-basedCorneal and lenticular deposits can occur with prolonged therapy. Usually asymptomatic but may progress. Also assess for retinal pigmentation.
Contraindications & Cautions for Chlorpromazine
Absolute Contraindications
- Known hypersensitivity to phenothiazines (cross-sensitivity within class).
- Comatose states or presence of large amounts of CNS depressants (alcohol, barbiturates, narcotics).
Relative Contraindications (Specialist Input Recommended)
- Previous phenothiazine-related jaundice or blood dyscrasia — do not re-expose unless benefits clearly outweigh risks.
- Bone marrow depression from any cause.
- Suspected Reye syndrome or encephalopathy in children — chlorpromazine’s antiemetic effect may mask diagnosis.
- Phaeochromocytoma — risk of severe hypotension.
Use with Caution
- Cardiovascular, hepatic, or renal disease
- Chronic respiratory disorders (suppresses cough reflex; risk of aspiration)
- Seizure history or concurrent anticonvulsant therapy (lowers seizure threshold)
- Elderly patients (increased sensitivity to hypotension, sedation, anticholinergic effects, TD)
- Narrow-angle glaucoma (anticholinergic mydriasis)
- Prostatic hypertrophy (urinary retention risk)
- Exposure to extreme heat or organophosphorus insecticides
FDA Boxed Warning
Increased Mortality in Elderly Patients with Dementia-Related Psychosis
Elderly patients with dementia-related psychosis treated with antipsychotic drugs are at an increased risk of death (1.6–1.7× versus placebo). Deaths were primarily cardiovascular or infectious. Chlorpromazine is not approved for dementia-related psychosis.
Patient Counselling for Chlorpromazine
Purpose of Therapy
Chlorpromazine helps control symptoms of mental health conditions such as schizophrenia or bipolar disorder by adjusting the balance of natural chemicals in the brain, particularly dopamine. It may also be prescribed for persistent hiccups, severe nausea, or to help you feel calmer before a procedure. It does not cure the underlying condition but can significantly improve symptoms when taken consistently.
How to Take
Take chlorpromazine at the same times each day, with or without food. Do not stop taking this medication abruptly without your prescriber’s guidance, as withdrawal symptoms (nausea, dizziness, tremor) may occur. Your dose will be adjusted gradually. Store tablets at room temperature away from light and moisture.
Drowsiness & Sedation
Tell patientDrowsiness is the most common side effect, especially during the first 1–2 weeks. It usually improves with time. Avoid driving or operating machinery until you know how this medication affects you. Avoid alcohol, as it makes drowsiness worse.
Call prescriberIf drowsiness remains severe after 2 weeks or interferes with daily activities.
Dizziness & Low Blood Pressure
Tell patientYou may feel lightheaded when standing up quickly. Rise slowly from sitting or lying positions. Drink plenty of fluids. This effect is more common with higher doses and injections.
Call prescriberIf you faint, fall, or feel persistently dizzy.
Sun Sensitivity
Tell patientChlorpromazine can make your skin very sensitive to sunlight. Wear protective clothing, apply sunscreen (SPF ≥30), and avoid prolonged sun exposure or tanning beds. A lip balm with SPF is also recommended.
Call prescriberIf you develop a severe sunburn or unusual skin discolouration.
Movement Problems
Tell patientYou may notice muscle stiffness, restlessness, or involuntary movements. These are less common with chlorpromazine than with some other antipsychotics but should be reported.
Call prescriberUrgently if you develop a stiff neck, difficulty swallowing, high fever with severe muscle rigidity, or uncontrollable movements of the face or tongue.
Jaundice Warning Signs
Tell patientRarely, chlorpromazine can affect the liver, especially in the first month. This is usually reversible when the medication is stopped.
Call prescriberImmediately if you notice yellowing of the eyes or skin, dark urine, persistent nausea, or flu-like symptoms with fever.
Sources
Regulatory (PI / SmPC)
- Chlorpromazine Hydrochloride Injection, USP. Full Prescribing Information. Novadoz Pharmaceuticals LLC. Drugs.com PIPrimary US label source for all FDA-approved indications, dosing, contraindications, boxed warning, and adverse reactions.
- Thorazine (chlorpromazine) Prescribing Information. RxListLegacy Thorazine label with detailed dosing tables for all indications including intractable hiccups, porphyria, and tetanus.
- Chlorpromazine Hydrochloride Tablets, USP. DailyMed label. DailyMedSource for oral tablet dosing including pediatric weight-based limits and psychotic vs nonpsychotic dosing in children.
Key Clinical Trials
- Leucht S, Cipriani A, Spineli L, et al. Comparative efficacy and tolerability of 15 antipsychotic drugs in schizophrenia: a multiple-treatments meta-analysis. Lancet. 2013;382(9896):951-962. DOINetwork meta-analysis placing chlorpromazine’s efficacy as mid-range among 15 antipsychotics.
- Adams CE, Awad GA, Rathbone J, Thornley B, Soares-Weiser K. Chlorpromazine versus placebo for schizophrenia. Cochrane Database Syst Rev. 2014;(1):CD000284. DOICochrane systematic review of 55 trials; confirms efficacy for relapse prevention but notes severe side-effect burden and poor trial quality.
- Kane J, Honigfeld G, Singer J, Meltzer H. Clozapine for the treatment-resistant schizophrenic: a double-blind comparison with chlorpromazine. Arch Gen Psychiatry. 1988;45(9):789-796. DOILandmark study establishing clozapine superiority over chlorpromazine in treatment-resistant schizophrenia; chlorpromazine as active comparator.
Guidelines
- Keepers GA, Fochtmann LJ, Anzia JM, et al. The American Psychiatric Association Practice Guideline for the Treatment of Patients with Schizophrenia. Am J Psychiatry. 2020;177(9):868-872. DOIAPA guideline recommending individualised antipsychotic selection; notes lower EPS but higher metabolic/sedative burden with low-potency FGAs.
Mechanistic / Basic Science
- Seeman P. Dopamine receptors and the dopamine hypothesis of schizophrenia. Synapse. 1987;1(2):133-152. DOIFoundational paper on D2 receptor binding affinity correlating with antipsychotic potency, using chlorpromazine as the reference compound.
- Snyder SH, Banerjee SP, Yamamura HI, Greenberg D. Drugs, neurotransmitters, and schizophrenia. Science. 1974;184(4143):1243-1253. DOIClassic paper demonstrating the correlation between clinical potency and dopamine receptor blockade for phenothiazines including chlorpromazine.
Pharmacokinetics / Special Populations
- Yeung PK, Hubbard JW, Korchinski ED, Midha KK. Pharmacokinetics of chlorpromazine and key metabolites. Eur J Clin Pharmacol. 1993;45(6):563-569. DOIPK study in 11 healthy men providing half-life (11 h IV; 23-37 h oral), Vd (~21 L/kg), and metabolite data.
- Chlorpromazine. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023. NCBIComprehensive clinical review of chlorpromazine pharmacology, dosing, side effects, and monitoring.
- Chlorpromazine hydrochloride. UK Poisons Information Document (UKPID). INCHEMDetailed PK reference including half-life range (8-35 h), protein binding (92-97%), bioavailability data, and overdose management.