Drug-induced parkinsonism. A reversible form of parkinsonism sometimes results from use of certain drugs, such as chlorpromazine and haloperidol, which are typically prescribed for patients with psychiatric disorders. Some drugs used for stomach disorders (metoclopramide), high blood pressure (reserpine), and others such as valproate can cause tremor and bradykinesia. Stopping the medication or lowering the dosage of these medications usually causes the symptoms to go away.