Why Men and Women Experience Pain and Pain Treatments Differently

Karen Lee Richards Health Guide
  • It has long been known that women and men experience pain, particularly chronic pain, very differently.  It has also been recognized since the mid-nineties that some opioid analgesics are more effective in women than men.  However, the reasons for these differences have remained a mystery – until now.

    We know that opioids decrease pain by activating opioid receptors, which are located on nerves that transmit painful sensations. Since levels of mu, delta, and kappa opiate receptors — the three main types of opioid receptor in the brain and spinal cord — are not thought to differ dramatically in men and women, it was difficult to understand why the effectiveness of some painkillers is dependent on sex.

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    Now, researchers at the State University of New York (SUNY) Downstate Medical Center have discovered that the same major types of opioid receptors interact differently, depending on sex.  The spinal cord of female laboratory animals was found to contain almost five times more of a mu-kappa opioid receptor complex than the spinal cord of male animals.

    Furthermore, the amount of mu-kappa complex in the spinal cord of the females was about four times higher when their levels of estrogen and progesterone were at their peak.  Subsequently, researchers found that both estrogen and progesterone are critical for the formation of the mu-kappa opioid receptor complexes.

    The discovery of a mu-kappa opioid receptor complex that is more prevalent in the spinal cord of females than males and that is synchronized with the ebb and flow of ovarian hormones could explain why drugs which primarily act on mu-opioid and kappa-opioid receptors are more effective at treating pain in women than men. 

    This research suggests that physicians should consider the stage of the menstrual cycle before deciding which drugs to prescribe to treat pain in women.  While some drugs might be very effective in treating pain at times when estrogen and progesterone levels are high, they could heighten pain when levels are low. 

    "This consideration could become even more critical in managing pain in postmenopausal and elderly women," said Dr. Gintzler, one of the study authors. "Further research is needed to flesh out these possibilities."

    The activation of the kappa-opioid receptor within the kappa-mu-opioid receptor complex could provide a mechanism for recruiting the pain-relieving functions of spinal kappa-opioid receptors without also activating their pain-promoting functions.

    My Thoughts...

    Well, ladies, although we tend to experience pain more often and with more intensity, and we have more chronic pain illnesses (like fibromyalgia, migraines and rheumatoid arthritis) than men, at least we also seem to respond better to pain-relieving medications.  That seems only fair. 

    All kidding aside, I think this is very interesting and promising research.  Admittedly, much of the  medical terminology in this study was over my head.  But I do know that understanding how our pain levels are tied to our hormone levels could lead to the development of more effective pain medications and more individualized prescribing and dosing. 

  • Hopefully, this new-found knowledge will also help scientists find a better, more effective pain reliever for men as well.  Perhaps future clinical trials for potential new pain medications should study their effectiveness for women and men separately.  I suspect that would yield more accurate and useful results.

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    Liu NJ, et al. Spinal Synthesis of Estrogen and Concomitant Signaling by Membrane Estrogen Receptors Regulate Spinal {kappa}- and {micro}-Opioid Receptor Heterodimerization and Female-Specific Spinal Morphine Antinociception. J Neurosci. 2011 Aug 17;31(33):11836-45.

    SUNY Downstate researchers identify possible new targets for treating pain in women. 2011 August 18. SUNY Downstate Medical Center. News Release.

Published On: August 24, 2011