This narrative review examines the effects of drug therapy on the natural history of Parkinson's disease. In terms of modifying the underlying disease process, it is possible that immediate therapy, rather than deferred treatment, can have a positive effect on the underlying disease process. However, it is unlikely that drug therapy has changed mortality from the condition and there is no evidence that it can delay the onset of non-motor features such as dementia and falls. The beneficial effects of drug therapy on the motor symptoms of Parkinson's disease are unquestionable, but these are at the expense of short-term dopaminergic side effects, long-term motor complications, and impulse control disorders. Major questions remain regarding which initial therapeutic approach should be taken which may possibly be answered by the ongoing PD MED trial. The beneficial effects of drug therapy on the motor features of Parkinson's disease have had a fundamental impact on the suffering of patients. The mainstay of these therapies continues to be levodopa, although it is now used at lower doses than in the past and in combination with other drug classes.