Impact of placebo assignment in clinical trials of Parkinson's disease

Informed consent procedures in placebo-controlled trials are developed to ensure that subjects entering studies clearly understand the possibility of placebo assignment. The extent of patient understanding and the impact of learning that they were assigned placebo treatment have not been extensively studied. By using a standardized questionnaire, we interviewed 50 consecutive placebo-treated patients from 14 placebo-controlled clinical trials of Parkinson's disease (PD) after completion of their involvement. All patients interviewed understood that their study contained a placebo arm. All had hoped to receive the study drug rather than placebo, and more than half the subjects believed they had improved clinically during their placebo exposure. Positive impressions of enrollment in placebo-controlled trials were more frequent than negative, included helping to advance science (86%); liking the experience, education, and attention associated with the clinical trial (90%); and participating in research for the benefit of other patients as well as for themselves (80%). If another placebo-controlled trial was offered, 88% expressed that they would possibly, likely, or definitely be interested in enrollment. PD patients clearly understand the concept of placebo-controlled trials they complete them, but they are inaccurate in assessing whether they received placebo treatment. Although most wish they received the active compound being tested, the overall view of participation in placebo-controlled trials is viewed very positively by PD patients.