n. any one of a group of drugs used to treat severe mental disorders (psychoses), including schizophrenia and mania; some are administered in small doses to relieve anxiety and tic disorders or to treat impulsivity in *emotionally unstable personality disorder. Formerly called major tranquillizers, and later typical and atypical antipsychotics, they are now known as first- and second-generation antipsychotics. The first-generation (or typical) antipsychotics include the *phenothiazines (e.g. *chlorpromazine), *butyrophenones (e.g. *haloperidol), and thioxanthenes (e.g. *flupentixol). Side-effects of antipsychotic drugs can include *extrapyramidal effects, sedation, *antimuscarinic effects, weight gain, and *long QT syndrome. The second-generation (or atypical) antipsychotics are a group of more recently developed drugs that are in theory associated with fewer extrapyramidal effects than first-generation antipsychotics: they include *clozapine, *risperidone, amisulpride, aripiprazole, olanzapine, and quetiapine. Antipsychotics act on various neurotransmitter receptors in the brain, including dopamine, histamine, serotonin, and cholinergic receptors. Most of them block neurotransmitter activity, but some have partially agonistic effects. Recent evidence suggests that there are significant differences among the second-generation antipsychotics regarding their efficacy and side-effect profiles. Clozapine, amisulpride, and olanzapine were found to be the most effective antipsychotics. Clozapine, zotepine, and olanzapine caused the most weight gain; haloperidol, zotepine, and chlorpromazine caused the most extrapyramidal side-effects; sertindole, amisulpride, and ziprasidone caused the most QT-prolongation; and clozapine, zotepine, and chlorpromazine caused the most sedation.
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