RESUMO
OBJECTIVE: To determine if the inclusion of a placebo control in clinical trials of schizophrenia affects retention rates in the first 35 days of inclusion relative to trials that did not have a placebo control. METHOD: This was a retrospective study of 8 double-blind clinical trials, 5 of which had a placebo control while 3 did not. Using survival analysis, retention rates between the placebo-controlled trials (PCTs) and the nonplacebo-controlled trials (NPCTs) were compared. Screening and percentage improvement on Brief Psychiatric Rating Scale and Positive and Negative Syndrome Scale scores were compared. RESULTS: Significantly more patients were retained in the 35-day period for NPCTs. Also, the PCT group had significantly more psychopathology at screening than did the NPCT group. CONCLUSIONS: Differences in retention rates between PCTs and NPCTs cannot be uniquely attributed to placebo itself.