Sex differences in analgesic responses: evidence from experimental pain models

Background and objective: Sex-related influences on the experience of pain have received considerable empirical attention. Women are at greater risk for several forms of clinical pain and exhibit greater perceptual responses to experimental pain. In recent years, investigators have turned their attention to the influence of sex-related factors on analgesic responses. The purpose of this review is to examine the literature on sex differences in analgesic responses, emphasizing findings from experimental studies. Methods: First, important methodological issues in laboratory pain research are presented, and sex differences in responses to experimentally-induced pain are briefly addressed. Next, previous data from non-human animal research and human experimental and clinical research related to sex differences in analgesia are discussed. Also, preliminary results are presented from an ongoing study in our laboratory examining analgesic responses in women and men. Results and conclusions: Both previous research and preliminary findings from our laboratory suggests that opioids produce greater analgesic responses in women than men. Potential mechanisms underlying sex differences in analgesia are proposed, and important directions for future research are suggested.