Chlorpromazine (Thorazine)

What it treats

Chlorpromazine is approved by the U.S. Food and Drug Administration for schizophrenia, severe behavioral problems in children, manic phases of bipolar disorder, intractable hiccups, nausea and vomiting, and preoperative anxiety. In practice today, the psychiatric use is mostly for schizophrenia, especially when sedation is a wanted effect or when cost matters. It's still used in general hospital medicine for stubborn hiccups and for some nausea situations.

It isn't usually first-line for maintenance treatment of schizophrenia in wealthy healthcare systems because the newer antipsychotics have gentler side-effect profiles. It remains important where availability and cost drive prescribing, and it has a real role in specific clinical situations where its sedating profile is useful.

How it works

Chlorpromazine is a first-generation antipsychotic. It blocks dopamine at the D2 receptor, which quiets the overactive dopamine signaling thought to drive hallucinations, delusions, and disorganized thinking. Unlike haloperidol, chlorpromazine also blocks histamine, muscarinic acetylcholine, and alpha-adrenergic receptors quite strongly, which is where much of its side-effect pattern comes from.

That broad receptor activity is why chlorpromazine is called low-potency: you need higher milligram doses to get the D2 effect, and along the way you get sedation, dry mouth, and blood pressure drop. It's also why acute movement side effects are somewhat less prominent than with high-potency drugs like haloperidol, because the anticholinergic action partly offsets them.

Receptor mechanism (detail)

Chlorpromazine is a D2 receptor antagonist with significant additional blockade at H1 histamine, alpha-1 adrenergic, and muscarinic M1 to M5 receptors. The H1 blockade drives sedation and appetite increase. The alpha-1 blockade causes orthostatic hypotension. The muscarinic blockade causes dry mouth, constipation, blurred vision, and urinary hesitancy, and it also partly offsets extrapyramidal effects. Chlorpromazine is the reference low-potency antipsychotic in the class, and 100 mg of chlorpromazine is used as the standard "one chlorpromazine equivalent" when comparing antipsychotic doses.

Potency and typical dosing pattern

Ranges are typical framework only, not a prescription for any individual. Chlorpromazine is low-potency, so the milligram numbers are much higher than for haloperidol or fluphenazine.

A typical starting range for schizophrenia is 25 to 75 mg per day, divided into two or three doses. The usual maintenance range is 300 to 800 mg per day, again divided. Doses can go higher in hospitalized patients. For intractable hiccups, 25 to 50 mg three or four times daily is the usual approach. For acute agitation in the hospital, 25 to 50 mg intramuscularly may be used. The prescriber sets the dose based on response, side effects, and the situation.

Safety monitoring

• Blood pressure, especially orthostatic vitals. Chlorpromazine causes blood pressure drops on standing, and this is a big driver of falls in older adults.
• Sedation and cognitive effects, tracked by patient report.
• Weight, BMI, fasting glucose or HbA1c, and lipids at baseline and annually. Metabolic effects are moderate.
• Liver function tests at baseline and if symptoms suggest a problem. Chlorpromazine can cause cholestatic jaundice, usually early in treatment.
• ECG at baseline and periodically, especially at higher doses or with other QTc-prolonging drugs.
• Involuntary-movement screen (AIMS) every six months for tardive dyskinesia.
• Complete blood count if unexplained fever, sore throat, or infection suggests possible agranulocytosis, which is rare but described.

Metformin co-commencement: Aoife Carolan / Schizophrenia Bulletin guideline.

A clinical guideline led by Aoife Carolan strongly recommends co-commencing metformin alongside high-risk antipsychotics like olanzapine or clozapine. This proactive approach helps mitigate severe metabolic side effects, significantly reducing antipsychotic-induced weight gain and improving insulin resistance. The Schizophrenia Bulletin guideline states that when prescribing olanzapine or clozapine, metformin should be initiated immediately to prevent weight gain and cardiometabolic issues. Chlorpromazine is a first-generation antipsychotic and isn't on the automatic co-commencement list, but metformin is recommended if weight rises more than 3 percent of pre-medication weight or if other cardiometabolic risk factors are present.

Typical titration used in the guideline: 500 mg once daily, then 500 mg twice daily after one week, then 500 mg increments every two weeks as tolerated, up to 1000 mg twice daily by about week six. Contraindicated with eGFR below 30 mL/min/1.73 m². Renal function is checked annually and metformin is held during acute illness or dehydration.

Source: Carolan A, et al. Metformin for the Prevention of Antipsychotic-Induced Weight Gain: Guideline Development and Consensus Validation. Schizophrenia Bulletin. 2025;51(5):1193 to 1203.

What to expect

Common side effects

• Sedation, especially early on.
• Orthostatic hypotension, dizziness on standing.
• Dry mouth, constipation, blurred vision, urinary hesitancy.
• Weight gain.
• Photosensitivity, sunburn happens more easily.
• Bluish-gray skin discoloration in sun-exposed areas with long-term high-dose use.
• Mild elevations in liver enzymes.

Serious side effects and warnings

Boxed warning. Chlorpromazine carries the FDA boxed warning that antipsychotics increase the risk of death in older adults with dementia-related psychosis, and it isn't approved for that use.

• Neuroleptic malignant syndrome. Rare but serious. High fever, muscle rigidity, confusion, autonomic instability. A medical emergency.
• Tardive dyskinesia. Long-term antipsychotic use can produce involuntary movements, especially of the face and mouth. Risk rises with dose and duration.
• Cholestatic jaundice. An immune-mediated liver reaction usually appearing in the first month. Reversible when the drug is stopped.
• Agranulocytosis. Rare but described. Unexplained fever or sore throat warrants a blood count.
• QTc prolongation at higher doses.
• Seizure threshold lowering, relevant in people with epilepsy.

This isn't medical advice. Any concern about a serious side effect should be raised with a prescriber promptly.

Sexual side effects

Chlorpromazine can lower sex drive, cause erectile problems, delay orgasm, or cause galactorrhea from raised prolactin. It can also cause retrograde ejaculation. If sexual side effects appear, it's worth raising with the prescriber, dose changes or a switch may help.

Weight, appetite, and sleep

Weight gain is common with chlorpromazine and generally moderate compared with olanzapine or clozapine but real. Appetite tends to increase. Sedation often helps sleep, and many people take the largest dose at bedtime. If daytime sedation is heavy, dose timing changes may help.

Starting and dosing basics

This section is general background, not a dosing instruction. The right dose is a decision for a prescriber. Chlorpromazine comes as tablets, an oral concentrate, and an injectable form used in hospital settings. It can be taken with or without food. Sun protection matters because of photosensitivity, sunscreen and covered clothing are worth planning for.

Missed doses and interactions

If you miss a dose, take it when you remember unless it's almost time for the next one. In that case, skip the missed dose and carry on. Don't double up.

Chlorpromazine interacts with many drugs. Other sedating medications, alcohol, blood pressure drugs, and other QTc-prolonging agents all matter. The prescriber and pharmacist need a full list of medications and supplements. Alcohol worsens sedation and orthostasis and is generally best avoided.

Stopping and tapering

Don't stop chlorpromazine abruptly if you've been on it a while. Sudden discontinuation can cause nausea, sweating, restlessness, and return of psychotic symptoms. A prescriber can step the dose down gradually.

Pregnancy and breastfeeding

Untreated psychosis carries its own risks in pregnancy, and chlorpromazine has decades of use with reassuring but limited data. It passes into breast milk. Anyone who's pregnant, planning a pregnancy, or breastfeeding should talk it through with their prescriber. This isn't medical advice.

Cost and generic availability

Chlorpromazine has been generic for decades and is inexpensive. Both oral and injectable forms are stocked in most pharmacies and hospitals. Insurance coverage is rarely an issue. Its low cost is one reason it remains widely used globally.

Common questions

Why isn't chlorpromazine used first-line anymore? Sedation, orthostatic hypotension, weight gain, and long-term tardive dyskinesia risk all pushed it down the list once atypical antipsychotics became affordable. It still has a role, but the newer drugs are usually gentler day-to-day.

Why do doses look so high compared with haloperidol? Chlorpromazine is low-potency, meaning each milligram does less D2 work. That's why 300 to 800 mg per day is a normal maintenance range while haloperidol lives in the 5 to 20 mg range. It doesn't mean chlorpromazine is stronger or weaker overall.

What is the "chlorpromazine equivalent"? Clinicians sometimes compare antipsychotic doses by converting them to chlorpromazine equivalents, with 100 mg of chlorpromazine as the reference point. It's a rough tool for talking about total antipsychotic exposure across different drugs.

Why does the sun matter? Chlorpromazine causes photosensitivity, so sunburn happens faster. Long-term high-dose use can also produce bluish-gray skin discoloration in sun-exposed areas. Sunscreen and clothing help.

Questions to ask your prescriber

• What are we hoping this treats, and how will we know it's working?
• How much daytime sedation should I expect?
• What should I do about sun exposure while I'm on this?
• Should we watch for movement side effects at each visit?
• If we decide to stop it later, how would we taper safely?

Sources

This guide draws on current prescribing information and public health references. It is reviewed for clinical accuracy and updated as guidance changes, and current as of June 8, 2026.

• U.S. Food and Drug Administration. Chlorpromazine prescribing information.
• MedlinePlus, U.S. National Library of Medicine. Chlorpromazine.
• National Institute of Mental Health. Mental health medications.
• American Psychiatric Association. Practice Guideline for the Treatment of Patients with Schizophrenia, 3rd edition.
• National Institute for Health and Care Excellence (NICE). CG178, Psychosis and schizophrenia in adults.
• Carolan A, et al. Metformin for the Prevention of Antipsychotic-Induced Weight Gain: Guideline Development and Consensus Validation. Schizophrenia Bulletin. 2025;51(5):1193 to 1203.