Hallucinations, delusions, and other psychotic symptoms can be caused by the drugs prescribed for PD. Reducing PD medications dosages or changing medications may be necessary if hallucinations occur. If such measures are not effective, doctors sometimes prescribe drugs called atypical antipsychotics, which include clozapine and quetiapine. The typical antipsychotic drugs, which include haloperidol, worsen the motor symptoms of PD and should not be used.