The conundrum of depression clinical trials: one size does not fit all

In this paper we review the history of antidepressant (AD) development, since the discovery of imipramine in 1957 to the present day. Through this exploration we will show that the increasing placebo response is likely a red herring and that a higher magnitude of placebo response is not an adequate explanation for AD trials’ high failure rates. As a better explanation for their lack of success, we will examine some of the fundamental flaws of AD clinical trials and their origins in historical forces. We focus on underpowering, which occurs as a consequence of unrealistic expectations for AD performance. In addition, we describe the lack of precision in the depression outcome measurements for the past 40 years and show how these measures contrast with those used in clinical trials of other chronic diseases, which use simpler outcome measures. Finally, we describe the role of regulatory agencies in influencing clinical trial design and how the assumption that ‘one size fits all’ for the past 60 years has led to flawed design of AD clinical trials.