Abstract
Treatment responses of placebo groups in addiction medicine trials have important implications for research methodology and clinical practice, however studies examining placebo group responses in addiction medicine are scarce. Extant data suggest the importance of early treatment responsiveness for long-term outcomes. Among methamphetamine-(MA) dependent individuals randomized to placebo pill plus behavioral support conditions in pharmacotherapy development trials, we hypothesized that immediate abstinence would be a necessary but insufficient predictor for end-of-trial (EOT) abstinence. The study is a secondary analysis of participants (n = 184; 36% female) in the placebo condition of three randomized, placebo-controlled methamphetamine dependence pharmacotherapy trials. Receiver operating characteristic (ROC) curve analyses assessed the predictive power of initial abstinence, assessed by thrice weekly urine samples, for EOT abstinence. Sixty percent of individuals with complete abstinence in the first two weeks of treatment were abstinent at EOT, while 18% of people who failed to meet this standard were abstinent at EOT. Early response was related to retention at EOT and 12-month follow-up. Findings suggest that the inability to achieve at least three MA negative screenings in the first two weeks is associated with greater than 90% likelihood of treatment failure. A third week of screening added minimally to the prediction of EOT outcomes. The prediction of treatment failure was more precise than the prediction of treatment success. The absence of a clinical response in the first two weeks of treatment among participants in the placebo group signals high risk of treatment failure. The majority of information regarding response in the placebo group from a 12-week trial is obtained early in the trial.