Sex-related hormonal influences on pain and analgesic responses

Considerable evidence indicates sex-related differences in pain responses a nd in the effectiveness of various analgesic agents. Specifically, females are at greater risk for experiencing many forms of clinical pain and are mo re sensitive to experimentally induced pain relative to males. Regarding an algesic responses, nonhuman animal studies indicate greater opioid analgesi a for males, while a limited human literature suggests the opposite. Though the mechanisms underlying these effects remain unclear, the influence of g onadal hormones on nociceptive processing represents one plausible pathway whereby such sex differences could emerge. The present article reviews the complex literature concerning sex steroid effects on pain responses and ana lgesia. First, nonhuman animal research related to hormonal effects on noci ceptive sensitivity and analgesic responses is presented. Next, human studi es regarding gonadal hormonal influences on experimental pain responses are reviewed. Several potential mechanisms underlying hormonal effects on noci ceptive processing are discussed, including hormonal effects to both periph eral and central nervous system pathways involved in pain transmission. Fin ally, based on these findings we draw several conclusions and make specific recommendations that will guide future research as it attempts to elucidat e the magnitude and importance of sex-related hormonal effects on the exper ience of pain. (C) 2000 Elsevier Science Ltd. All rights reserved.