Expectation-induced placebo effect on acute sadness in women with major depression: An experimental investigation

Abstract

Background: Meta-analyses demonstrate that placebo effects play an important role in antidepressant treatment. Expectations seem to constitute a highly relevant placebo mechanism in this context. This study investigated whether an expectation manipulation combined with the intake of an active placebo could reduce acute sadness in depressed participants following a sadness-inducing mood manipulation.

Methods: Women who suffered from a major depressive episode (N = 94) were randomly allocated to the drug expectation group (expectation to receive a fast-operating antidepressant), the placebo expectation group (expectation to receive a placebo) or the no treatment group (no expectation, no placebo). The drug expectation and the placebo expectation group received a placebo. All participants watched a sadness-inducing film. Sadness was assessed at baseline, after randomization and after placebo intake and mood induction. Data were analyzed by a 3 × 3 analysis of variance.

Results: There were significant between-group differences in sadness change from the baseline after mood induction. While sadness increased in the no treatment group, it did not change in the placebo expectation group. In the drug expectation group, sadness even decreased.

Limitations: Only a single medication intake was simulated. Effects on acute sadness do not allow inferences about depression symptoms.

Conclusion: This experimental study found a placebo effect on sadness in clinically depressed participants. The effects were even larger than expected. Future research must investigate placebo effects on depression symptoms as well as long-term placebo intake.

Keywords: Expectations; Major depression; Placebo; Randomized controlled trials; Sadness.