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Note to media: See abstract 479

New findings on the lessebo effect in Parkinson's disease may be game-changer for study design

SYDNEY – A study assessing the lesser-known lessebo effect in Parkinson’s disease and the challenges it presents to study organizers was presented today at the 17th International Congress of Parkinson’s Disease and Movement Disorders. Future study designs will need to carefully consider the lessebo effect, which are negative feelings a study subject may have about the possibility of receiving a placebo, and how those feelings can impact the efficacy of a new drug being tested.

Tiago Mestre, MD, MSc, Toronto Western Hospital, and colleagues conducted a systematic review of double blind randomized controlled trials (RCTs) of dopamine agonists in Parkinson’s disease (PD) using either a placebo or active control. Placebos are widely used for RCTs. The effect size of the UPDRS-III change was measured based on the presence or absence of a placebo arm and the probability of placebo assignment. Preliminary results showed that a placebo arm reduces the measured efficacy of an active treatment in RCTs.

“The study points out that clinical trial designs strongly impact results. In Europe, comparator trials are much more commonly performed than in North America, so we also may have to consider cultural differences in the study populations in explaining these interesting results,” states Christopher Goetz, MD, Rush University, Chicago, IL, USA. “If enrolling in a placebo-controlled trial of a new drug actually dampens the impact of the study treatment itself, the bar is very high for demonstrating a clear superiority of the study treatment.”

About the 17th International Congress of Parkinson's Disease and Movement Disorders:
Meeting attendees are gathered to learn the latest research findings and state-of-the-art treatment options in Movement Disorders, including Parkinson's disease. More than 2,000 physicians and medical professionals from 70 countries will be able to view over 1,300 scientific abstracts submitted by clinicians from around the world.

About The Movement Disorder Society:
The Movement Disorder Society, an international society of over 4,000 clinicians, scientists, and other healthcare professionals, is dedicated to improving patient care through education and research. For more information about The Movement Disorder Society, visit