Antipsychotic Selection, Monitoring & Adverse Effects
Every antipsychotic has a signature harm; choose around it and monitor for it
How antipsychotics work
D2 blockade in four pathways. Every antipsychotic blocks dopamine D2 receptors, and the pathway explains both benefit and harm. In the mesolimbic tract, blockade relieves positive symptoms such as hallucinations and delusions. In the nigrostriatal tract it produces extrapyramidal symptoms (EPS). In the tuberoinfundibular tract it removes dopamine's tonic inhibition of prolactin, causing hyperprolactinemia. In the mesocortical tract it can worsen negative and cognitive symptoms.
Generations. First-generation (typical) agents are graded by D2 potency. Second-generation (atypical) agents add 5-HT2A antagonism, which lowers EPS risk but brings more metabolic toxicity for several drugs. Aripiprazole is a D2 partial agonist, which is why it lowers rather than raises prolactin. Because efficacy is similar across agents other than clozapine, selection is driven by each drug's side-effect profile and the patient's comorbidities.
Side-effect profiles and selection
High-potency first-generation agents. Haloperidol and fluphenazine bind D2 tightly, so EPS, hyperprolactinemia, and neuroleptic malignant syndrome are the main risks, while sedation, orthostasis, anticholinergic effects, and weight gain are minimal. IV haloperidol, especially at high doses, prolongs QT and can cause torsades de pointes.
Low-potency first-generation agents. Chlorpromazine and thioridazine block H1 (sedation, weight gain), α1 (orthostatic hypotension), and muscarinic receptors (dry mouth, constipation, urinary retention, blurred vision, confusion). Their intrinsic anticholinergic activity means fewer EPS. Thioridazine prolongs QT and causes retinal pigmentation; chlorpromazine causes photosensitivity and corneal or lens deposits.
Second-generation signatures. Olanzapine and clozapine cause the most weight gain, insulin resistance, type 2 diabetes, and dyslipidemia (especially hypertriglyceridemia), partly through H1 and 5-HT2C blockade. Risperidone and its metabolite paliperidone cause the most hyperprolactinemia and dose-dependent EPS. Ziprasidone has the largest QTc effect among oral agents and must be taken with food. Quetiapine is strongly sedating and orthostatic with intermediate metabolic risk but very low EPS and little prolactin effect. Aripiprazole and lurasidone, together with ziprasidone, are the most weight-sparing, but akathisia is their characteristic complaint; aripiprazole has been linked to impulse-control problems such as gambling, and lurasidone must be taken with food.
| Drug | Metabolic | Prolactin | EPS | Signature concern |
|---|---|---|---|---|
| Haloperidol | Low | High | High | Dystonia, NMS; QT when IV |
| Chlorpromazine | Moderate | Moderate | Low | Sedation, orthostasis, anticholinergic |
| Olanzapine | Highest | Low–moderate | Low | Weight gain, diabetes, lipids |
| Clozapine | Highest | Low | Lowest | Neutropenia, myocarditis, seizures, ileus |
| Risperidone, paliperidone | Moderate | Highest | Dose-dependent | Galactorrhea, amenorrhea, gynecomastia |
| Quetiapine | Moderate | Low | Very low | Sedation, orthostasis |
| Ziprasidone | Low | Low | Low | QT prolongation |
| Aripiprazole, lurasidone | Lowest | Lowers (aripiprazole) | Low | Akathisia |
Hyperprolactinemia. Symptoms include galactorrhea, oligomenorrhea or amenorrhea, infertility, sexual dysfunction, and gynecomastia; the resulting hypogonadism lowers estrogen and testosterone and causes bone loss over time. Check prolactin with a pregnancy test and TSH, then lower the dose or switch to a prolactin-sparing agent, classically aripiprazole (adding low-dose aripiprazole also works). Image the pituitary if prolactin is very high or not explained by the drug.
QT prolongation. Obtain a baseline ECG when cardiac disease, other QT-prolonging drugs, or hypokalemia or hypomagnesemia are present, and avoid ziprasidone, IV haloperidol, and thioridazine when QTc is prolonged; a QTc above 500 ms carries high torsades risk.
Matching drug to patient. With obesity, diabetes, or dyslipidemia choose aripiprazole, lurasidone, or ziprasidone; with prolactin symptoms, aripiprazole; with parkinsonism, quetiapine or clozapine; with insomnia or agitation, quetiapine or olanzapine. In Parkinson disease or Lewy body dementia psychosis, quetiapine, clozapine, or pimavanserin is used, because haloperidol and risperidone worsen parkinsonism.
Metabolic monitoring and management
Schedule. Every patient starting an antipsychotic needs a personal and family history of diabetes, obesity, dyslipidemia, and cardiovascular disease, plus measurements repeated as drug-induced changes emerge.
| Measure | Baseline | Follow-up |
|---|---|---|
| Weight and BMI | Yes | Monthly for 3 months, then quarterly |
| Waist circumference | Yes | Yearly |
| Blood pressure | Yes | 12 weeks, then yearly |
| Fasting glucose or A1c | Yes | 12 weeks, then yearly |
| Lipid panel | Yes | 12 weeks, then yearly |
Managing weight gain. Start with diet and exercise counseling. If the patient is psychiatrically stable, switch to a lower-risk agent (aripiprazole, ziprasidone, lurasidone). When switching would risk relapse, add metformin, which attenuates antipsychotic-induced weight gain and insulin resistance. Treat diabetes, dyslipidemia, and hypertension to standard targets.
Movement disorders and other serious reactions
| Syndrome | Onset | Features | Treatment |
|---|---|---|---|
| Acute dystonia | Hours to days | Torticollis, oculogyric crisis, laryngospasm; young men | IM benztropine or diphenhydramine |
| Akathisia | Days to weeks | Inner restlessness, pacing | Lower dose, propranolol, benzodiazepine |
| Parkinsonism | Weeks | Bradykinesia, rigidity, tremor | Lower dose, benztropine, amantadine |
| Tardive dyskinesia | Months to years | Lip smacking, tongue thrusting, choreoathetosis | Reduce or switch drug; valbenazine or deutetrabenazine |
Tardive dyskinesia. It follows prolonged D2 blockade, may be permanent, and is screened for with the AIMS exam. Reduce or switch the antipsychotic (clozapine and quetiapine carry the lowest risk) and add a VMAT2 inhibitor. Anticholinergics do not help and may worsen it, and raising the antipsychotic dose only masks it temporarily.
Fever, lead-pipe rigidity, autonomic instability, altered mental status, and a high CK after starting or increasing an antipsychotic signal neuroleptic malignant syndrome: stop the drug and give supportive care. Antipsychotics also carry a boxed warning for increased mortality in older adults with dementia-related psychosis.
Clozapine and long-acting injectables
Indications. Clozapine is the only antipsychotic proven superior in treatment-resistant schizophrenia, defined as failure of at least two adequate trials of different antipsychotics (about 6 weeks each at a therapeutic dose with good adherence). It also reduces suicidal behavior in schizophrenia and schizoaffective disorder and has the lowest EPS and tardive dyskinesia risk.
Neutropenia. Severe neutropenia or agranulocytosis requires a baseline ANC of at least 1,500/μL, then ANC checks weekly for 6 months, every 2 weeks for months 6–12, and monthly thereafter. Therapy is interrupted if ANC falls below 1,000/μL, and fever or sore throat prompts an urgent ANC. The FDA removed the clozapine REMS in 2025, so ANC results no longer have to be reported before dispensing, but labeling still recommends this monitoring.
Myocarditis and other toxicities. Myocarditis appears mainly in the first 4–8 weeks with fever, tachycardia, chest pain, dyspnea, and rising troponin and CRP; clozapine is stopped and the heart evaluated with ECG and echocardiogram. Cardiomyopathy can develop later. Seizures are dose-dependent. Nocturnal sialorrhea is common and responds to glycopyrrolate. Gastrointestinal hypomotility can progress to fatal ileus, so a bowel regimen and questions about stool frequency are routine. Orthostasis, tachycardia, sedation, and major weight gain complete the profile.
Tobacco smoke induces CYP1A2. When a patient quits smoking, clozapine and olanzapine levels rise, causing sedation and seizures; nicotine replacement does not prevent this.
Long-acting injectables. For patients who relapse because they miss oral doses, long-acting injectables (haloperidol or fluphenazine decanoate, risperidone, paliperidone palmitate, aripiprazole, olanzapine pamoate) guarantee delivery and reduce relapse. Confirm tolerability with the oral form of the same drug first. Olanzapine pamoate can cause post-injection delirium/sedation syndrome, so patients are observed for 3 hours after each injection.