Early in the course of the disease, most patients will respond very well to medical therapy. The most useful and most commonly prescribed medication is Sinemet, a precursor compound that is converted to dopamine by an enzymatic process that takes place in the brain.

At this stage, treatment with Sinemet may fully control symptoms of the disease. With time however, several changes will often take place. The most fundamental of these changes is the progression of the underlying disease process. This progression can take the form of bilateral involvement (affecting both sides of the body) worsening of the early symptoms, and the development of severe problems with gait, postural stability, and ability to perform basic tasks of daily life. This progression is usually treated with increasing Sinemet dosages as well as the addition of other medications.

These increased dosage regimens may cause a variety of side effects. One of the most prevalent and problematic side effects of dopaminergic medications like Sinemet is the development of dyskinesias. These are characterized by unwanted writhing movements that are prevalent at the peak of a medication dose. Additionally, some patients will fluctuate very rapidly between the 'off' and 'on' states and require very complex medication regimens.