The Unsolved Problem of Attrition Rates on Randomized Clinical Trials for Cocaine Use Disorders: A Scoping Review

Background: Cocaine use disorder (CUD) is a significant and insufficiently studied public health issue, especially considering that the global prevalence of CUD is estimated to be higher than ever. There is still no consensus on effective treatments for CUD. Important barriers for research in the field include the high attrition levels observed in randomized controlled trials (RCTs) for CUD treatment and the lack of emphasis on methods to reduce attrition in CUD RCTs. Methods: The goal of this study was to systematically review over 2 decades of CUD RCTs, with the objective of evaluating the reporting of attrition bias and methods used to mitigate attrition. Results: Our scoping review extracted information from 106 RCTs, of which only 82 explicitly evaluated attrition as an outcome. Thirty-eight studies had an attrition rate above 50%, and five 16 studies had medium attrition bias, 6% to 19%. The remaining 68 had large attrition bias. Conclusion: Across all included studies, discussion of attrition as a limitation was uncommon. Overall, these analyses suggest that most RCTs evaluating CUD treatments have not adequately accounted for attrition in their analyses or employed approaches to mitigate attrition.