A method for modifying Parkinson's disease by periodically administering a pharmaceutical composition comprising a therapeutically effective amount of rasagiline or a pharmaceutically acceptable salt of rasagiline to the patient, thereby modifying the disease. The method includes reducing the rate of progression; delaying the need for symptomatic anti-Parkinsonian therapy; reducing the risk of a Parkinson's disease patient requiring symptomatic anti-Parkinsonian therapy; and reducing the functional decline.
