Placebo/nocebo symptom reporting in a sham herbal supplement trial

The present study examined reports of placebo and nocebo symptoms in a college sample. The study was presented under the guise of a clinical trial to evaluate the effectiveness of an over-the-counter herbal supplement intended to enhance cognitive performance. Participants were informed they would be receiving either an herbal supplement or a placebo, and each was provided with a mock list of possible beneficial and adverse effects of the supplement. In fact, all participants received placebo. Symptoms were endorsed by a significant majority of participants following placebo ingestion. More important, results indicated that the few participants who believed they received an herbal supplement endorsed (via self-report) significantly more symptoms than those who believed they received a placebo. Neither anxiety nor social desirability was significantly related to symptom reporting. Results suggest that beliefs concerning treatment received may subsequently affect the degree of placebo response in a no-treatment group. Implications for clinical trials and future research are discussed.