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Patient expectancy mediates placebo effect in antidepressant trials
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Patient expectancy significantly mediated placebo effects in antidepressant trials, according to recent findings.
“Placebo responses in antidepressant trials have become a critical issue for the development of novel therapeutics and the treatment of patients in clinical settings. On the one hand, increasing placebo response complicates efforts to detect signals of efficacy for new agents in the drug development setting,” Bret R. Rutherford, MD, assistant professor of clinical psychiatry at Columbia University College of Physicians and Surgeons, New York State Psychiatric Institute, New York, and colleagues wrote. “On the other hand, practicing clinicians know that many patients will not experience sustained remission of their depression with currently available treatments.”
To determine if patient expectancy mediates placebo effects in antidepressant studies, researchers conducted a prospective, randomized controlled trial among adult outpatients with major depressive disorder. Study participants were assigned to receive open (n = 26) or placebo-controlled citalopram treatment (n = 20). After assessing pre- and post-randomization expectancy, participants received citalopram or placebo for 8 weeks.
Post-randomization expectancy scores were significantly higher among participants who received open citalopram treatment (mean = 12.1), compared with the placebo-controlled group (mean = 11).
Mixed-effects modeling indicated a significant week-by-group interaction, in which Hamilton Depression Rating Scale (HAM-D) scores decreased faster among the open group than the placebo-controlled group.
Post-randomization patient expectations partially mediated group effects on HAM-D scores at week 8.
“Strikingly, despite receiving the identical antidepressant medication, being treated by the same study clinicians, and visiting the same treatment site, depressed subjects who knew they were receiving citalopram improved on average 6 HAM-D points more than those receiving citalopram who were aware they had a chance of receiving placebo. This difference between citalopram outcomes under high compared with low expectancy conditions is greater in magnitude than the typically observed differences between drug and placebo in antidepressant trials, testifying to the powerful influence of expectancy-based placebo effects on depressive symptoms,” the researchers wrote. “Developing interventions capable of modifying patient expectancy may reduce placebo response in the drug development setting and improve medication response in community treatment.” – by Amanda Oldt
Disclosure: Rutherford reports consulting fees from Pfizer. Please see the full study for a list of all authors’ relevant financial disclosures.