Research results have been mixed, some finding that men required more morphine after surgery than women. A very large Chinese study found women used significantly less morphine when using patient-controlled analgesia post-operatively, indicating that cultural, ethnic or genetic factors may account for differing research results. But in animal models, male rats exhibited greater analgesia than female rats to equal doses of opioids.
The researchers wrote that, “Sex differences in pain perception have been attributed to a different socialization process for men and women that influences bodily experience and the willingness to communicate distress. Hormone variations could also in part explain sex differences in pain experience and response to morphine.”