Imaginary pills and open-label placebos can reduce test anxiety by means of placebo mechanisms

Placebos have been shown to be beneficial for various conditions even if administered with full transparency. Hence, so-called open-label placebos (OLPs) offer a new way to harness placebo effects ethically. To take this concept one step further, this study aimed at evaluating placebo effects without the use of a physical placebo, i.e., by imagining taking a pill. Healthy students (N = 173) with self-reported test anxiety were either randomized to an imaginary pill (IP; n = 55), an OLP (n = 59) or a control group (CG; n = 59). Both intervention groups were instructed to take two pills daily for three weeks. Primary outcome was test anxiety, secondary outcomes were sleep quality, general well-being and test performance. Groups test anxiety differed at study-endpoint, F(2,169) = 11.50, p < .001. Test anxiety was lower in the intervention groups compared to the CG, t(169) = − 4.44, p < .001, d = − 0.71. The interventions did not differ significantly, i.e., both were similarly efficacious, t(169) = 0.61, p = .540, d = 0.11. The interaction between group and time in explaining test anxiety was significant, F(5,407.93) = 6.13, p < .001. OLPs and IPs reduced test anxiety in healthy participants compared to the CG. This finding opens the door for a novel and ethical method to harness placebo effects.