The reversal of established medical practice is common and occurs across all classes of medical practice. This investigation sheds light on low-value practices and patterns of medical research.

The Frequency of Medical Reversal W e use the term reversal to signify the phenomenon of a new trial-superior to predecessors because of better design, increased power, or more appropriate controls-contradicting current clinical practice. In recent years, a number of such reversals have occurred. Use of hormone therapy, 1 the class 1C antiarrhythmic agents, 2 and the pulmonary artery catheter 3 have decreased when trials demonstrated that they are either less effective than previously thought or harmful. Reversal not only affects medications and diagnostic tests. Previously accepted indications for surgical and medical procedures have also been contradicted. In 2007, the Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation (COURAGE) 4 trial found no benefit to support percutaneous coronary intervention (vs optimal medical therapy) in many patients with stable coronary artery disease, an indication that was previously accepted. The implications of reversal are notable. Reversal implies error or harm to patients who underwent the practice in question, during the years it was considered effective. Reversal also undermines trust in the medical system. We sought to estimate the frequency of reversal by examining 1 year of original publications in the New England Journal of Medicine. Other researchers have studied the rate of reversal in medical research. 5 Studies of medical interventions are often followed by studies that either reach the opposite result or suggest the magnitude of effect was initially overestimated. Among high-citation count publications, Ioannidis 5 found that 16% were contradicted by future studies, and another 16% were found to have smaller effects than initially thought. Herein, we focused on existing practices that were contradicted in a given period in highimpact literature. Knowing the rate of, and predisposing factors for, reversal may have implications for the approval of medical therapies. Methods. We reviewed all Original Articles in the New England Journal of Medicine in 2009 (the last complete year of the publication at the time of our investigation).