In a study of responses to St. John's wort, sertraline, and placebo, Justin Chen, Class of 2013, and colleagues showed that patients who believed they were receiving active therapy rather than placebo obtained greater improvement, independent of treatment. They found that patient beliefs regarding treatment may have a stronger association with clinical outcome than the actual medication received, and the strength of this association may depend upon the particular combination of treatment guessed and treatment received.
Chen JA, Papakostas GI, Youn SJ, Baer L, Clain AJ, Fava M, Mischoulon D. (2011) Association between patient beliefs regarding assigned treatment and clinical response: reanalysis of data from the Hypericum Depression Trial Study Group. J Clin Psychiatry. 2011 Dec;72(12):1669-76.