Fear of pain reduces the effect of a placebo intervention on pain

Abstract

Placebo analgesia refers to a reduction in pain after a placebo treatment has been provided. Fear of pain has been shown reduce placebo analgesic response. The present study investigated if experimentally induced fear of pain reduces the efficacy of a placebo intervention on pain. A balanced within-group design (n = 45) with a natural history, a placebo, and a placebo+fear condition was employed. In the placebo condition the participants were exposed to heat stimuli before and after administration of placebo capsules with information that they were given an analgesic. In the placebo+fear condition the participants were told, after the administration of the placebo capsules, that they would receive electric shocks before the next block of heat stimuli. On group level we found no placebo effects on reported pain intensity, pain unpleasantness and stress. We thus restricted our analysis to those who actually showed a reduction in pain after the administration of placebos (n = 18). In these respondents we observed that the placebo effect was diminished in the placebo+fear condition, however fear of pain did not predict placebo response in this group. In the startle reflex data we found a placebo effect on group level (n = 45). This placebo effect was reduced in the placebo+fear condition. The participants showed a potentiated startle reflex immediately after the induction of fear of pain, preventing a placebo response on pain to occur. Experimentally induced fear of pain thus seems to be related to a reduced placebo response.