KILLING THE PAIN

By LEON JAROFF

Poets and lovers, as well as doctors, have long expounded on the differences between the sexes. But none have ever given much thought to the possibility that men and women might react differently to pain killers.

None, that is, until Dr. Jon Levine and his team at the University of California, San Francisco, took pains to investigate. Using drugs called kappa opioids, a form of opiate commonly used to ease labor pains, they gave intravenous doses to 28 men and 20 women, all in their early 20s, who had just had wisdom teeth extracted.

To the surprise of the researchers, who report in the current Nature Medicine, the two sexes showed a striking difference in their responses. While the women were still generally pain-free three hours after having their teeth pulled, the males had no such luck. Their relief was slight and lasted only about an hour. No comparable gender difference in pain relief has yet been found with the more powerful and widely used opiates such as morphine and codeine.

Why do kappa opioids favor females? Could estrogen, the female hormone, somehow enhance the drugs' effectiveness, or might the male hormone, testosterone, hamper it? Another possibility, Levine suggests, is that women's brains have more--or more responsive--kappa receptors, enabling the kappa opioids to block pain more effectively.

While earlier tests had concluded that these opioids are not effective pain killers, other than for labor, some doctors suspect the results may have been skewed by a preponderance of male test subjects. Indeed, Levine now suggests that kappa opioids might be generally used to treat acute pain in women. Unlike morphine-like drugs, they have few unpleasant side effects, and they are not addictive.

--By Leon Jaroff