No evidence for an acute placebo effect on emotional processing in healthy volunteers

Placebo-controlled trials are the gold standard measure of efficacy in the development of new treatments for depression. However, the large placebo effects associated with standard measures of subjective symptoms reduce the sensitivity of such trials to detect antidepressant effects. There is a need to develop novel efficacy markers that are resistant to placebo effects. Measures of emotional processing, known to be sensitive to antidepressant treatment, may be such a marker, although the effect of an acute placebo treatment on these measures remains unclear. We assessed the influence of placebo on a validated battery of emotional processing tasks, the Emotional Test Battery (ETB), in healthy participants. Participants were informed they might receive the antidepressant drug bupropion, placebo or no treatment, with placebo effect being estimated as the difference between the placebo and no treatment groups. We found no significant difference between these groups on measures of emotional processing. There was also no effect of subjective treatment expectancy on performance in the tasks. This suggests that the ETB might be a useful tool for Phase I trials assessing novel antidepressant agents against placebo.