Placebo hypoalgesia: racial differences.

No large-cohort studies that examine potential racial effects on placebo hypoalgesic effects exist. To fill this void, we studied placebo effects in healthy and chronic pain participants self-identified as either African American/black (AA/black) or white. We enrolled 372 study participants, 186 with a diagnosis of temporomandibular disorder (TMD) and 186 race-, sex-, and age-matched healthy participants to participate in a placebo experiment. Using a well-established paradigm of classical conditioning with verbal suggestions, each individual pain sensitivity was measured to calibrate the temperatures for high- and low-pain stimuli in the conditioning protocol. These 2 temperatures were then paired with a red and green screen, respectively, and participants were told that the analgesic intervention would activate during the green screens to reduce pain. Participants then rated the painfulness of each stimulus on a visual analog scale ranging from 0 to 100. Racial influences were tested on conditioning strength, reinforced expectations, and placebo hypoalgesia. We found that white participants reported greater conditioning effects, reinforced relief expectations, and placebo effects when compared with their AA/black counterparts. Racial effects on placebo were observed in TMD, although negligible, short-lasting, and mediated by conditioning strength. Secondary analyses on the effect of experimenter-participant race and sex concordance indicated that same experimenter-participant race induced greater placebo hypoalgesia in TMDs while different sex induced greater placebo hypoalgesia in healthy participants. This is the first and largest study to analyze racial effects on placebo hypoalgesia and has implications for both clinical research and treatment outcomes.