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Treatment studies use placebo to control for patient expectations, but placebo groups may not account for individual variations. Laboratory studies of placebo effects usually use inert substances, which may not mimic effects of pharmacologically active agents. To address these gaps in knowledge, researchers studied how belief about drug effects influenced analgesia with intravenous infusion of a mu-opioid receptor agonist, whose action begins and ends within a few minutes. Participants were 22 healthy volunteers who were given applications of painful heat to their calves.
In this cross-over study, participants underwent functional magnetic resonance imaging (MRI) while being exposed to a series of experimental conditions: (1) saline, not dru…