Sildenafil (Viagra) for the Treatment of Dyskinesias in Parkinson's Disease

Inclusion Criteria: 1. Diagnosis of idiopathic Parkinson's disease, Hoehn and Yahr stage 2.0 to 4.0. 2. Presence of drug-induced dyskinesias 3. Age\>40 years. 4. Willingness and ability to comply with the study requirements and give informed consent. Exclusion Criteria: 1. Atypical parkinsonian syndrome due to drugs, metabolic disorders, encephalitis, or degenerative diseases. 2. History of stereotaxic brain surgery. 3. Clinical history of dementia. 4. Known major psychiatric disorder, major depression, schizophrenia. Known alcoholism or substance dependence within previous 12 months. 5. History of major hematological, renal, or hepatic abnormalities. 6. Known coronary artery disease including angina or myocardial infarction within the last 6 months. Significant cardiovascular disease including cardiac failure, unstable angina or life-threatening arrhythmia within the last 6 months. 7. History of stroke within the last 6 months. 8. Abnormal EKG consistent with cardiac ischemia. 9. Treatment with nitrates. Nitrates or any NO donors in any dosage form (oral, sublingual, transdermal, inhalation, or aerosols). 10. Malignant hypertension or SBP . 180 or \<90, or DBP .110 or \<50. 11. History of priapism. 12. Known history of retinitis pigmentosa. 13. Positive pregnancy test. 14. History of bleeding disorder. 15. Patients with active peptic ulcer disease associated with bleeding. 16. Unwillingness to use adequate contraceptive methods if of childbearing potential. 17. Patients with medical or psychological condition or social circumstances that would impair their ability to participate in the study. 18. Use of Viagra or any experimental drugs within 30 days of screening visit.