a newer class of antipsychotic drugs that produce fewer extra pyramidal effects compared to the original typical version. They are also less likely to alter serum levels of prolactin and appear to be less likely to cause tardic dyskinesia - all of which are significant adverse effects of the typical antipsychotic drugs. They show some degree of activity as dopamine receptor antagonists, but also block the effects of serotonin and other neurotransmitters. Atypical antipsychotics are used in the treatment of schizophrenias, delusional disorders, dementias, and in cases where behavior is violent and unpredictable. The prototype of the group of drugs is clozapine. Others in current clinical use include olanzapine, risperidone, and quetiapine. There have been complaints that this class of drugs causes extreme weight gain in some cases. Also known as novel antipsychotics- second-generation antipsychotics.