Beliefs About Medicines Predict Side-Effects of Placebo Modafinil

BACKGROUND: Patients receiving placebo in clinical trials often report side-effects (nocebo effects), but contributing factors are still poorly understood. PURPOSE: Using a sham trial of the cognition-enhancing "smart pill" Modafinil we tested whether medication beliefs and other psychological factors predicted detection and attribution of symptoms as side-effects to placebo. METHODS: Healthy students (n = 201) completed measures assessing beliefs about medication, perceived sensitivity to medicines, negative affectivity, somatization, and body awareness; 66 were then randomized to receive Deceptive Placebo (told Modafinil-given placebo, 67 to Open Placebo (told placebo-given placebo, and 68 to No Placebo. Memory and attention tasks assessed cognitive enhancement. Nocebo effects were assessed by symptom checklist. RESULTS: More symptoms were reported in the Deceptive Placebo condition (M = 2.65; SD = 2.27) than Open Placebo (M = 1.92; SD = 2.24; Mann-Whitney U = 1,654, z = 2.30, p = .022) or No Placebo (M = 1.68; SD = 1.75, Mann-Whitney U = 1,640, z = 2.74, p = .006). Participants were more likely to attribute symptoms to Modafinil side-effects if they believed pharmaceuticals to be generally harmful (incidence rate ratio [IRR] = 1.70, p = .019), had higher perceived sensitivity to medicines (IRR = 1.68, p = .011), stronger concerns about Modafinil (IRR = 2.10, p < .001), and higher negative affectivity (IRR = 2.37, p < .001). CONCLUSIONS: Beliefs about medication are potentially modifiable predictors of the nocebo effect. These findings provide insight into side-effect reports to placebo and, potentially, active treatment.