Experimental Approach to Inducing Anti-Histaminergic Placebo Effects: A Randomized Controlled Trial in Healthy Volunteers

Participants of all groups experienced a reduction in itch, while wheal size was only reduced in those participants with high expectations. These expectation effects align with prior research but should be carefully tested in future studies. Taken together, these results support the theory of differing mechanisms between patients with lived experience and healthy participants. Future studies should investigate the underlying neuropsychological mechanisms of expectation-induced anti-histaminergic effects.