Levine: I think it opens up an area of research that we're really at the beginning of.

Narrator: This is Science Today. Dr. Jon Levine of the University of California, San Francisco was interested in whether there were differences in the way men and women respond to pain relievers. After having wisdom teeth extracted, his subjects were given a class of narcotic known as kappa-opioids, which had a reputation as a weak drug. Levine found that kappa-opioids didn't relieve the men's pain -- but worked for the women just fine. It's the first known gender difference in a pain reliever -- but perhaps not the last.

Levine: We need to go back now to the laboratory to look and see what kind of biological differences might exist -- 081 what differences exist between men and women that may explain such dramatic differences in how men and women may respond to this class of agents, and whether or not they may even respond differently to other classes of agents that we use in the treatment of moderate to severe pain.

Narrator: Levine says other researchers are going back and re-analyzing old research and finding similar results. For Science Today, I'm Steve Tokar.