antipsychotic

An antipsychotic is a drug used to treat psychosis — the hallucinations, delusions, and disordered thinking seen in schizophrenia and related conditions. If overactive dopamine signalling is like a stuck-open valve flooding certain brain pathways with 'salience,' antipsychotics turn that valve back down.

All clinically effective antipsychotics block dopamine D2 receptors, particularly in the mesolimbic pathway, which dampens the positive symptoms of psychosis. They split into two broad groups: first-generation ('typical') drugs such as haloperidol, which block D2 strongly, and second-generation ('atypical') drugs such as risperidone, olanzapine, quetiapine, and clozapine, which also block serotonin 5-HT2A receptors and tend to cause fewer movement side effects.

Besides schizophrenia, antipsychotics are used in bipolar mania, severe agitation, as add-ons in resistant depression, and for some forms of nausea. Effects on agitation appear quickly, but full antipsychotic benefit develops over weeks.

Blocking dopamine elsewhere causes characteristic problems: movement disorders (parkinsonism, acute dystonia, and the often-irreversible tardive dyskinesia) from the nigrostriatal pathway, and raised prolactin from the tuberoinfundibular pathway. Atypicals trade some of these for metabolic effects like weight gain and diabetes risk; clozapine is uniquely effective but requires blood monitoring for agranulocytosis.