Rabbit syndrome secondary to risperidone.

After taking risperidone for 4 months, a 38-year-old man with a major depressive disorder experienced rabbit syndrome. This uncommon extrapyramidal side effect is characterized by rhythmic movements of the mouth and may be caused by typical antipsychotics and risperidone secondary to blockade of dopamine D2 receptors. The syndrome, whose exact mechanism is unknown, responded to anticholinergic treatment in this patient. A literature review indicated that most recent cases have occurred as reactions to the atypical antipsychotic risperidone. Changing treatment to an atypical antipsychotic other than risperidone, such as olanzapine 10 mg/day, may lead to suppression or elimination of the syndrome.