Women Really Are the Stronger Sex: Female Hormones Outperform Opioids in Pain Relief

New research could transform how we treat chronic pain—especially in women

For centuries, the battle of the sexes has sparked debate across everything from intellect to endurance. But a groundbreaking new study from UC San Francisco adds serious weight to one side of the scale: when it comes to pain relief, women might actually be biologically stronger.

Researchers have discovered that the female hormones estrogen and progesterone naturally trigger the body to produce its own opioids—chemicals that suppress pain more effectively than some pharmaceutical painkillers. In essence, women’s hormones are capable of activating a biological pain relief system within the body, one that rivals medication—and this discovery could revolutionise how we approach chronic pain treatment.

A Natural Painkiller Built into the Female Body

The study, published in Science, reveals a new role for a specific type of immune cell known as T regulatory cells, or T-regs. These cells were previously known for their ability to reduce inflammation, but now researchers have found that in females, T-regs do much more: they actually produce enkephalin, a natural opioid, when stimulated by estrogen and progesterone.

These hormones effectively tell the T-regs, located in the meninges—the protective tissue around the brain and spinal cord—to release pain-relieving compounds. This newly uncovered pathway between hormones, immune cells, and the nervous system helps to block pain signals before they reach the brain.

Why This Matters—Especially for Women in Pain

This could be a game-changer for the 20% of Americans living with chronic pain, a condition that is often under-treated, misunderstood, and more common in women than men. According to the U.S. Pain Foundation, over 51 million adults in the U.S. experience persistent pain. The cost? Up to $635 billion each year in healthcare, lost productivity, and disability.

The study also offers clues into why postmenopausal women—who no longer produce estrogen and progesterone—experience more chronic pain, and why certain medications, like some migraine treatments, work better for women than for men.

The Gender Gap in Pain Research

Lead researcher Elora Midavaine called the findings “very unusual,” noting that this hormone-cell interaction has nothing to do with immunity—which is what T-regs were previously known for. Instead, this pain-relief function seems to be a sex-specific adaptation, highlighting a profound biological difference in how pain is processed and managed by male and female bodies.

When researchers removed T-reg cells from the spinal cord region of mice, only female mice became more sensitive to pain—a clear sign that women’s bodies rely more heavily on this mechanism.

“It was both fascinating and puzzling,” said co-author Dr. Sakeen Kashem. “It actually made me skeptical initially.”

What’s Next? From Mice to Medicine

The next phase of the research is even more ambitious: the team is exploring whether T-regs could be genetically engineered to produce enkephalin continuously in both men and women. If successful, this could offer a groundbreaking, hormone-free treatment for millions of people suffering from pain that current medications fail to relieve.

Dr. Allan Basbaum, who co-led the study, said the ultimate goal is to develop new therapies that mimic or enhance this hormone-pain pathway, potentially offering a safer alternative to opioids—especially in the wake of an ongoing opioid crisis.

A New Lens for Gender-Specific Medicine

This research opens up a new frontier in understanding not just how women experience pain differently, but why—on a cellular, hormonal, and neurological level. It also underscores the importance of factoring biological sex into drug development, diagnosis, and treatment plans.

And perhaps most importantly, it shifts the narrative. For years, women’s pain has been minimised or dismissed. This study offers scientific validation that female bodies are not just different—they're biologically equipped with powerful pain management systems.

As researchers continue to explore this promising discovery, one thing is clear: when it comes to enduring and managing pain, women may truly be the stronger sex.