Why painkillers are more effective in women than men

A new study has found out why the effectiveness of some painkillers is different between women and men.

While it has been recognized since the mid—nineties that some narcotic analgesics are more effective in women than men, the reason for this difference was largely unknown.

Narcotic analgesics 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.

Now, the new research by researchers at the State University of New York revealed that the same major types of opioid receptor interact differently, depending on sex. The spinal cord of female laboratory animals was found to contain almost five times more kappa—mu heterodimer—a complex of mu—opioid and kappa—opioid receptor—than the spinal cord of male animals.

The study further suggests that kappa—mu opioid receptor heterodimers could function as a molecular switch that shifts the action of kappa—opioid receptors and endogenous chemicals that act on them from pain promoting to pain alleviating. Kappa—mu opioid receptor heterodimers could serve as a novel molecular target for pain management in women.

Alan Gintzler, PhD, professor of biochemistry, Department of Obstetrics and Gynecology, and his senior collaborators Sumita Chakrabarti, PhD, and Nai—Jiang Liu, PhD, at the SUNY Downstate Medical Center, conducted the research.

The study was published in the Proceedings of the National Academy of Sciences and the Journal of Neuroscience.