When treating patients with psychoses, clinicians must often consider changing their treatment from one antipsychotic agent to another. The transition may be necessary because the patient experiences serious side effects or because the existing therapy no longer controls the patient's symptoms. A principal problem in changing antipsychotic agents is the potential for withdrawal symptoms resulting from discontinuation of the existing therapy. These syndromes can manifest as reemergence or worsening of psychosis, rebound or unmasked dyskinesia, and cholinergic-rebound symptoms. Withdrawal signs and symptoms may include insomnia, nausea, vomiting, anxiety, and agitation. When switching a patient to the new antipsychotic agent risperidone, the clinician can keep withdrawal symptoms to a minimum by considering the patient's clinical history and current status. For some patients, abrupt withdrawal of the current antipsychotic may be possible. For others, the dose of the previous medication must be gradually reduced before risperidone is initiated. In many cases, the transition is best made by overlapping the existing therapy and risperidone.