Chlorpromazine is a first-generation antipsychotic medicine used to treat schizophrenia, mania, severe agitation, nausea, vomiting and intractable hiccups. Introduced in 1952, chlorpromazine was the first effective drug treatment for schizophrenia and is widely regarded as the medicine that transformed modern psychiatry. It is listed on the National List of Essential Medicines (NLEM) as an essential drug.

Drug Class: First Generation (Typical) Antipsychotic

Chlorpromazine belongs to the phenothiazine class of antipsychotic medicines, which are categorised as first generation or typical antipsychotics. First-generation antipsychotics are distinguished from second-generation antipsychotics by their higher affinity for dopamine D2 receptors. This strong dopamine blockade is responsible for both the antipsychotic effectiveness and the characteristic movement related side effects of chlorpromazine. Within the first-generation antipsychotics, chlorpromazine is a low-potency agent that requires a relatively high milligram dose to achieve its antipsychotic effect and tends to cause more sedation and autonomic side effects but fewer movement-related side effects than high-potency agents such as haloperidol.

Historical Significance - The First Modern Antipsychotic

Chlorpromazine holds a unique place in the history of medicine as the drug that made modern psychiatry possible. Chlorpromazine was first used clinically in psychiatry by French psychiatrists Jean Delay and Pierre Deniker in 1952. Within a few years it had been adopted worldwide and had transformed the management of schizophrenia.

Impact on psychiatry: Before chlorpromazine psychiatry had no effective pharmacological treatments for psychosis. Its introduction triggered decades of research into antipsychotic medicines and the dopamine hypothesis of schizophrenia.

Medical Uses: Schizophrenia, Mania, Nausea, Hiccups

Chlorpromazine is used across a range of psychiatric and non-psychiatric medical conditions where its dopamine-blocking and sedative properties are clinically useful. Common uses are:

• Schizophrenia and other psychotic disorders: Chlorpromazine reduces positive symptoms of psychosis such as hallucinations, delusions and disorganised thinking. It is used for both acute and maintenance treatment of schizophrenia, schizoaffective disorder and other psychotic conditions. It is less effective for negative symptoms such as social withdrawal and emotional flattening.

• Acute mania and bipolar disorder: Chlorpromazine is used in the management of acute manic episodes in bipolar disorder particularly when rapid sedation and control of agitation are needed, and is sometimes used alongside mood stabilisers.

• Nausea, vomiting and intractable hiccups: Chlorpromazine is an effective antiemetic because it blocks dopamine receptors in the chemoreceptor trigger zone (CTZ) in the brainstem.

• Severe agitation and preoperative sedation: Chlorpromazine's strong sedative properties make it useful for managing severe agitation in acute psychiatric emergencies and for providing preoperative sedation in patients who are very anxious or agitated.

How Chlorpromazine Works 

Chlorpromazine exerts its antipsychotic effects primarily by blocking dopamine D2 receptors in specific brain pathways, reducing dopamine overactivity responsible for positive symptoms such as hallucinations and delusions. Chlorpromazine also blocks histamine H1 receptors (causing sedation), muscarinic acetylcholine receptors (causing dry mouth, constipation, blurred vision and urinary retention), and alpha-1 adrenergic receptors (causing postural hypotension), which explains chlorpromazine's significant sedation and autonomic side effects.

Common Side Effects 

Chlorpromazine produces a wide range of side effects that reflect its broad blockade of multiple receptor types in the brain and body. They are:

• Sedation and drowsiness

• Postural (orthostatic) hypotension

• Anticholinergic side effects like dry mouth, constipation, blurred vision, urinary retention and increased heart rate

• Weight gain 

• Increased sensitivity of the skin to sunlight in patients on long-term treatment.

Serious Risks: Tardive Dyskinesia and EPS

The most serious neurological side effects of chlorpromazine are caused by its blockade of dopamine D2 receptors in the nigrostriatal pathway - the brain circuit that controls movement. This causes:

• Extrapyramidal side effects (EPS): Include drug-induced parkinsonism (tremor, stiffness and slowness of movement), akathisia (an intensely distressing inability to sit still), acute dystonia (sudden, painful, sustained muscle contraction affecting the neck, jaw or eyes), and tardive dyskinesia. The good news is these symptoms usually respond well to a dose adjustment or additional medication.

• Tardive dyskinesia (TD): It is a serious and potentially irreversible movement disorder developing after months to years of antipsychotic treatment, characterised by repetitive, involuntary movements of the tongue, lips, face or limbs - most visibly seen as lip smacking, tongue protrusion or chewing movements. Unlike EPS it may not go away even after stopping the drug, which is why regular monitoring matters so much during long-term use.

Neuroleptic Malignant Syndrome - Rare but Serious

Neuroleptic malignant syndrome (NMS) is a rare but life-threatening reaction to antipsychotic medicines including chlorpromazine that requires immediate emergency medical treatment. NMS is characterised by four cardinal features: severe muscle rigidity, hyperthermia (very high body temperature often above 40°C), autonomic instability (fluctuating blood pressure, rapid heart rate and excessive sweating) and altered consciousness ranging from confusion to coma. It usually occurs within days to weeks of starting treatment or increasing the dose. Risk factors include rapid dose increases, dehydration, and extreme heat. Treatment involves immediate stopping of the antipsychotic medicine, hospital admission (often to an intensive care unit), aggressive cooling measures, intravenous fluids to prevent kidney damage from rhabdomyolysis and in severe cases, dantrolene (a muscle relaxant) or bromocriptine (a dopamine agonist). 

Who Should Not Take Chlorpromazine?

Chlorpromazine is contraindicated in certain patient groups and should be used with great caution in others. They are:

• Patients with bone marrow suppression or severe liver disease: Chlorpromazine can cause agranulocytosis and should not be taken by patients with bone marrow disease. Chlorpromazine is also extensively metabolised in the liver and has been associated with cholestatic jaundice, making it unsuitable in patients with severe liver disease.

• Elderly patients with dementia: Antipsychotics including chlorpromazine are associated with a higher risk of stroke, excessive drowsiness, postural hypotension and excessive sedation. 

• People with Parkinson's disease: Chlorpromazine can worsen movement problems. 

• People with a prolonged QT interval or certain heart rhythm disorders: Chlorpromazine can increase the risk of dangerous abnormal heart rhythms. Patients who already have a prolonged QT interval or who are taking other QT-prolonging medicines should not take chlorpromazine.

Drug Interactions That Matter in Psychiatric Care

Chlorpromazine has clinically important interactions with several classes of medicines. They are:

• Alcohol

• Anaesthetic agents

• Anticholinergic medicines such as amitriptyline and trihexyphenidyl

• Antihypertensive medicines such as amlodipine, atenolol, ramipril or enalapril

• Benzodiazepines such as diazepam and clonazepam

• Lithium 

• Medicines that prolong the QT interval including antibiotics (azithromycin, ciprofloxacin), antimalarials (chloroquine, hydroxychloroquine), antifungal medicines (fluconazole) and other antipsychotics

• Opioid painkillers such as tramadol and codeine.

Chlorpromazine vs Haloperidol vs Newer Antipsychotics

Understanding how chlorpromazine compares to other antipsychotics helps doctors and patients make informed treatment choices.

• Chlorpromazine vs haloperidol: Haloperidol is a high-potency first-generation antipsychotic requiring a much lower milligram dose (5 to 20 mg daily) compared to 300 to 800 mg daily for chlorpromazine and causes far more extrapyramidal side effects than chlorpromazine but much less sedation and fewer autonomic side effects. 

• Chlorpromazine vs second-generation antipsychotics (olanzapine, risperidone): Second-generation antipsychotics cause far fewer extrapyramidal side effects than chlorpromazine and are effective for both positive and negative symptoms of schizophrenia. Olanzapine causes significantly more weight gain and metabolic side effects (elevated blood sugar, elevated cholesterol). Risperidone causes more prolactin elevation than chlorpromazine, leading to menstrual irregularities and breast milk production in women.

• Role of chlorpromazine in modern practice: Chlorpromazine is now rarely the first choice for schizophrenia in well-resourced settings, where second-generation antipsychotics are preferred. However chlorpromazine retains its role in acute management of severe agitation, in the treatment of intractable hiccups and in resource-limited settings in India.

FAQs

1. What is chlorpromazine used for?

   Chlorpromazine is used to treat schizophrenia, acute mania, severe agitation, nausea and vomiting and intractable hiccups. In schizophrenia it reduces positive symptoms such as hallucinations, delusions and disorganised thinking. It is also the only USFDA-approved medicine for intractable hiccups.

2. Is chlorpromazine still used today or has it been replaced?

   Chlorpromazine is still used today though second-generation antipsychotics such as olanzapine and risperidone have largely replaced it as first-line treatments for schizophrenia in well-resourced hospitals. Chlorpromazine remains in use in India's public psychiatric hospitals and rural areas where access to newer antipsychotics is limited and retains specific clinical roles in intractable hiccups and management of severe acute agitation.

3. What is tardive dyskinesia and can chlorpromazine cause it?

   Tardive dyskinesia (TD) is a movement disorder caused by prolonged antipsychotic use, characterised by repetitive, involuntary, writhing movements of the tongue, lips, face and limbs (like lip smacking, tongue protrusion or chewing movements). Chlorpromazine does cause tardive dyskinesia, with the risk increasing with duration of treatment and older age. Many patients on long-term first-generation antipsychotics develop tardive dyskinesia and it may not fully resolve even after the antipsychotic is stopped.

4. Can chlorpromazine be used for nausea and vomiting?

   Yes chlorpromazine is an effective antiemetic for nausea and vomiting caused by medicines, medical conditions or surgery. The antiemetic dose of chlorpromazine is lower than the antipsychotic dose, though ondansetron, domperidone, and metoclopramide are now preferred in India for routine nausea and vomiting.

5. Why does chlorpromazine cause so much sleepiness?

   Chlorpromazine causes significant sedation primarily because it blocks histamine H1 receptors in the brain, which are responsible for promoting wakefulness and alertness. Chlorpromazine also blocks alpha-1 adrenergic receptors, which contributes to further drowsiness and a drop in blood pressure. 

6. What are extrapyramidal side effects (EPS) from chlorpromazine?

   Extrapyramidal side effects (EPS) are movement disorders caused by chlorpromazine's blockade of dopamine D2 receptors in the nigrostriatal pathway. EPS from chlorpromazine include muscle stiffness, tremors, slowed movements (drug-induced parkinsonism), restlessness (akathisia), and painful muscle spasms (acute dystonia).

7. Is chlorpromazine safe for elderly patients with dementia?

   Chlorpromazine is generally not recommended for elderly patients with dementia. All antipsychotics carry a warning that their use in elderly patients with dementia-related psychosis is associated with a significantly increased risk of stroke. Chlorpromazine is particularly unsuitable in this group because of its additional risks: strong sedation and postural hypotension increase the risk of falls and anticholinergic side effects (dry mouth, constipation, urinary retention, confusion) are particularly problematic in elderly patients.

8. How long does chlorpromazine take to work for psychosis?

   The sedative and calming effects of chlorpromazine begin within hours of the first dose, which is why it is useful for managing acute agitation. The full antipsychotic effect takes much longer to develop with most patients showing meaningful improvement within 2 to 4 weeks and maximum improvement after 6 to 8 weeks of consistent daily treatment.

9. Can chlorpromazine affect the heart rhythm?

   Chlorpromazine prolongs the QT interval on an ECG. Prolongation of the QT interval increases the risk of a dangerous irregular heart rhythm called torsades de pointes, which can degenerate into ventricular fibrillation and sudden cardiac arrest. The risk is greatest when chlorpromazine is combined with other QT-prolonging medicines such as antimalarials (chloroquine, hydroxychloroquine) or certain antibiotics.

10. What is neuroleptic malignant syndrome and is chlorpromazine a cause?

    Neuroleptic malignant syndrome (NMS) is a rare but life-threatening reaction to antipsychotic medicines characterised by severe muscle rigidity, very high body temperature (often above 40°C), autonomic instability (fluctuating blood pressure and sweating) and altered consciousness. Chlorpromazine is a recognised cause of NMS, as are all antipsychotics.

References

1. Delay J, Deniker P, Harl JM. Therapeutic method derived from hibernotherapy in excitation and agitation states. Ann Med Psychol (Paris). 1952;110(2):267–73. https://pubmed.ncbi.nlm.nih.gov/14956490

2. 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):951–62. https://doi.org/10.1016/S0140-6736(13)60733-3

3. Tarsy D, Baldessarini RJ. Epidemiology of tardive dyskinesia: is risk declining with modern antipsychotics?. Mov Disord. 2006;21(5):589–98. https://doi.org/10.1002/mds.20823

4. Gurrera RJ, Caroff SN, Cohen A, et al. An international consensus study of neuroleptic malignant syndrome diagnostic criteria using the Delphi method. J Clin Psychiatry. 2011;72(9):1222–8. https://doi.org/10.4088/JCP.10m06438

5. Siskind D, McCartney L, Goldschlager R, Kisely S. Clozapine v. first- and second-generation antipsychotics in treatment-refractory schizophrenia: systematic review and meta-analysis. Br J Psychiatry. 2016;209(5):385–92. https://doi.org/10.1192/bjp.bp.115.177121