Pain Relievers Work Differently in Men and Women

March 26 -- More than 50 million Americans live with chronic pain, while millions more suffer bouts with acute pain due to injuries or surgery.

And while both men and women endure this affliction, pain is not always an equal opportunity burden: women are more apt than men to suffer from chronic pain and experience more severe and longer lasting pain.

Moreover, research shows that men and women also respond differently to pain medications and an increasing number of studies suggest that the fundamental biology of pain and pain relief differs between the sexes.

In fact, accumulating evidence implies that the days of sex-specific pain killers — perhaps pink and blue pills — may not be too far off.

The first hint that pain medication might work differently in men and women came as a surprise to researchers at the University of California at San Francisco (UCSF). They gave morphine-like painkillers called "kappa opioids" to patients who had undergone surgery to remove their wisdom teeth.

The drugs gave more powerful and long-lasting pain relief to women compared with men. In addition, at some doses, kappa-opioids were exceptionally good pain relievers in women and actually made the pain worse for men. Understanding the cause of this discrepancy will lead to better pain relief for both sexes.

Sex-specific pain relief is not just a phenomenon confined to opioids. Recent research shows that ibuprofen, the active ingredient in a number of over-the-counter medicines, may be much less effective in women than men.

Researchers at the University of New South Wales in Australia randomly gave a small group of men and women either ibuprofen or a sugar pill and then used electricity to cause experimental pain. They discovered that ibuprofen gave significant pain relief only in men.

New Research Implicates Genetics

New research by Jeffrey S. Mogil, professor of psychology at McGill University in Montreal, Canada, suggests that men and women use separate mechanisms in the brain to achieve pain relief.