Medical complications of new antipsychotic drugs.

Although antipsychotic drugs have a high therapeutic index (ratio of clinical benefit to adverse effects), they are associated with a range of adverse effects in most patients. The majority of these side effects are tolerable, readily managed, and not life threatening. The most troublesome side effects are neurological. Two new antipsychotics (clozapine and risperidone) have recently been introduced and are the first of a new generation of compounds that may further improve the therapeutic index of routine antipsychotic drug administration. Clozapine clearly has a reduced risk of drug-induced parkinsonism, akathisia, and tardive dyskinesia, while producing an increased risk of agranulocytosis, seizures, and weight gain. Risperidone at low doses produces relatively few parkinsonian side effects, but it can cause tardive dyskinesia (though relative risk remains to be established). Risperidone has not been associated with blood dyscrasias or increased risk of seizures, but weight gain can be a problem for some patients. Neuroleptic malignant syndrome has been reported with both drugs, but relative risk has not been established.