Antipsychotics block dopamine activity to reduce psychotic symptoms. Typical antipsychotics (first-generation) effectively treat positive symptoms but cause movement disorders. Atypical antipsychotics (second-generation) treat positive and negative symptoms with reduced movement side effects but metabolic risks. Long-term use is essential for maintaining remission in schizophrenia.
From your study of schizophrenia-spectrum disorders, you know that psychosis involves positive symptoms — hallucinations, delusions, disorganized thinking — and negative symptoms — flat affect, poverty of speech, reduced motivation. From your study of the dopamine system, you know that dopamine pathways project from midbrain nuclei to distinct brain regions, each mediating different functions. Antipsychotic pharmacology is built on exploiting this anatomy: by blocking dopamine D2 receptors selectively in the mesolimbic pathway, it is possible to reduce psychotic symptoms, while ideally sparing other pathways that depend on dopamine for critical functions.
Typical (first-generation) antipsychotics — haloperidol, chlorpromazine, fluphenazine — are potent, nonselective D2 receptor antagonists. They block D2 receptors throughout all four major dopamine pathways simultaneously. Their effectiveness against positive symptoms reflects the dopamine hypothesis: overactivity in the mesolimbic pathway is thought to underlie hallucinations and delusions, and blocking D2 there reduces this signal. However, blocking D2 in the nigrostriatal pathway — which coordinates movement — produces extrapyramidal side effects (EPS): Parkinson-like rigidity and tremor, restlessness (akathisia), and with chronic use, the potentially irreversible tardive dyskinesia. Blocking D2 in the mesocortical pathway, which already shows reduced dopamine activity in schizophrenia, can worsen negative symptoms and cognitive function rather than improving them.
Atypical (second-generation) antipsychotics — clozapine, olanzapine, risperidone, quetiapine — were developed to reduce EPS while maintaining antipsychotic efficacy. They achieve this through a combination of mechanisms: weaker or faster-dissociating D2 block (the "fast-off" hypothesis), combined D2 and serotonin 5-HT2A antagonism (serotonin modulates dopamine release, and blocking 5-HT2A in the nigrostriatal pathway preserves dopamine tone), and action at additional receptor targets. The atypicals, particularly clozapine, also show meaningful improvement in negative symptoms and cognition, possibly because the serotonin-dopamine balance in the prefrontal cortex is more favorably adjusted. The tradeoff is metabolic side effects — weight gain, dyslipidemia, elevated blood glucose — which significantly increase cardiovascular risk with long-term use.
The therapeutic rationale for long-term antipsychotic use in schizophrenia rests on two facts: psychosis causes neurobiological damage (each episode is associated with further cortical thinning and cognitive decline), and relapse rates after discontinuation are very high. This creates a difficult clinical calculus — the benefits of sustained remission must be weighed against the progressive metabolic and neurological risks of chronic medication. Understanding antipsychotics means understanding not just their acute receptor pharmacology, but also how the brain adapts to sustained receptor blockade (D2 receptor upregulation, for instance, may explain why dose reduction often precipitates relapse) and why selecting the right agent requires matching the patient's symptom profile and risk tolerance to each drug's receptor profile.