Placebo Responses in Trials of Parkinson's Disease.

Parkinson's disease is well documented to be associated with a placebo response. The striatonigral degeneration and resulting dopamine deficiency make it a particularly compelling condition for studying placebo effects, which are most commonly explained by a hyperdopaminergic hypothesis. The placebo response can vary across different motor and nonmotor symptoms. Several factors may influence this response, including symptom severity, the presence of motor fluctuations, expectation of benefit, and the type of intervention. While minimizing placebo effects is essential in clinical trials-where strategies exist to reduce bias-a placebo response can be leveraged in clinical practice to improve patient outcomes.