TUESDAY, Oct. 22 (HealthDay News) -- Intranasal application of the hormone oxytocin enhances the placebo response, according to a research letter published in the Oct. 23/30 issue of the Journal of the American Medical Association.
Simon Kessner, from the University Medical Center Hamburg-Eppendorf in Germany, and colleagues recruited 75 healthy male volunteers who were randomly assigned to receive 40 IU of oxytocin (37 participants) or saline intranasally. After 45 minutes, two identical inert ointments were applied to two sites on each participant's forearm, although one was described as an anesthetic. A calibration procedure identified the individual stimulation intensity at which a 20-second painful heat stimulus was perceived as a 60 on a visual analogue scale (VAS; ranging from 0 [no pain] to 100 [unbearable pain]).
The researchers found that pain ratings for the placebo site were significantly lower compared with the control site across both treatment groups, despite identical thermal stimulation. In the oxytocin group, the placebo analgesic response was significantly higher compared to the saline group. There were no significant differences between the groups related to temperature levels needed to induce a VAS score of 60, pain ratings on the control site, adverse effects, and post hoc treatment guesses, thus, consistent with oxytocin having no analgesic effect.
"To our knowledge, our study provides the first experimental evidence that placebo responses can be pharmacologically enhanced by the application of intranasal oxytocin," the authors write. "Based on its effects on trust and empathy, we hypothesize that oxytocin might have increased the believability of the instructions by the study physician."
One author disclosed financial ties to the pharmaceutical industry.
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