Every antipsychotic medication, without exception, blocks D2 dopamine receptors. This shared mechanism reduces the positive symptoms of psychosis — hallucinations, delusions, disorganized thinking — by reducing mesolimbic dopamine signaling. But D2 blockade in the nigrostriatal pathway produces a familiar set of motor side effects, collectively called extrapyramidal symptoms or EPS.
The EPS family includes several distinct phenomena. Acute dystonia appears within hours to days of starting the medication: sustained muscle contractions, often in the neck (torticollis), face, or eyes (oculogyric crisis). Akathisia is an inner restlessness with an urge to move; patients pace, cannot sit still, and describe the sensation as deeply distressing. Drug-induced Parkinsonism is the classic triad — bradykinesia, rigidity, tremor — emerging within weeks. Tardive dyskinesia emerges after months to years, with involuntary repetitive movements of the face, tongue, and limbs that may persist even after the drug is stopped.
First-generation antipsychotics (haloperidol, fluphenazine, chlorpromazine, perphenazine) are high-affinity D2 blockers with relatively pure dopaminergic action. They are effective for positive symptoms of psychosis but produce EPS frequently, especially at higher doses. They are still used clinically — haloperidol remains a workhorse in agitation, delirium, and acute psychosis — but they have largely been displaced as first-line treatment for chronic schizophrenia.
Second-generation antipsychotics (risperidone, olanzapine, quetiapine, ziprasidone, aripiprazole, paliperidone) block D2 alongside serotonin 5-HT2A receptors. The 5-HT2A antagonism is thought to partly protect the nigrostriatal pathway from full D2 effect, reducing EPS at typical doses. The trade-off is metabolic side effects — weight gain, dyslipidemia, insulin resistance, and increased risk of diabetes. Olanzapine and clozapine are the worst offenders; aripiprazole and ziprasidone less so.
Clozapine deserves special mention. It is the most effective antipsychotic for treatment-resistant schizophrenia, with substantially better outcomes than alternatives in patients who have failed two adequate antipsychotic trials. But it carries the risk of agranulocytosis — a rare but potentially fatal drop in white blood cell count — requiring weekly to monthly blood monitoring. The clinical decision to start clozapine is significant, and the monitoring is non-negotiable.
When you prescribe any antipsychotic, picture the basal ganglia gate. You are partially blocking the dopaminergic signal that opens it. The patient's psychosis quiets — and so does the rest of the dopaminergic motor and cognitive system. The skill is finding the dose that quiets the psychosis without crippling the rest.