When Swiss researchers at the University of Geneva analyzed blood samples from 94 conscripts aged 18 to 23, they uncovered something that defies decades of conflicting claims about cannabis and male hormones: cannabis use does not lower testosterone, and may actually boost it by about 23 percent in young men.
The contradiction matters because the scientific community has long debated whether cannabis damages the male reproductive system. Some studies suggested it reduces sperm count and motility, a concern many assumed was rooted in hormonal disruption. But the evidence remained messy and contradictory, leaving both researchers and the public uncertain about what cannabis actually does to the endocrine system.
A team led by Professor Serge Rudaz at the University of Geneva's Section of Pharmaceutical Sciences, working with the Swiss Center for Applied Human Toxicology, designed a study to cut through the noise. Rather than focusing narrowly on testosterone alone—as most previous research had done—they analyzed hundreds of steroid hormones in plasma samples from 47 confirmed cannabis users and 47 non-users. This broader approach revealed something crucial: the increase in testosterone wasn't coming from the adrenal glands, but directly from the testes themselves, specifically from Leydig cells that manufacture the hormone.
"Our results show that cannabis use would lead to an increase of about 23% in testosterone in young men," Rudaz explained. "But by taking a closer look at all male sex hormones—the androgens—we were able to locate the source of this increase specifically in the testes."
The finding opens a door to a second, equally significant discovery. The research team identified two new hormonal biomarkers that could help detect regular cannabis use: hydroxyprogesterone (11B-OHP4) and dihydroprogesterone (5B-DHP4). These progesterone metabolites increase so dramatically in cannabis users that they could serve as reliable markers for monitoring endocrine disruption from regular cannabis exposure. According to Mathieu Galmiche, the study's first author and now a researcher at the Karolinska Institutet in Stockholm, this finding should push the scientific community to examine hormones that have been overlooked until now.
But there is an important caveat: higher testosterone does not mean better sperm quality or improved fertility. The relationship between testosterone and fertility is far more complex than a simple equation. The testosterone increase among cannabis users could reflect the body's compensatory response to reduced sensitivity of androgen receptors when cannabis is present. Alternatively, men with naturally higher testosterone levels might simply be more prone to risk-taking behavior, making them more likely to use cannabis in the first place.
The researchers remain cautious about drawing broader conclusions. While cannabis appears to affect biological mechanisms related to reproduction, the exact clinical implications for young men's fertility remain unclear. They emphasize that further research is needed to determine whether a toxicity threshold exists and to assess potential long-term effects.
The study, published in Communications Medicine, represents a step forward in untangling a complicated relationship. By broadening their hormonal analysis beyond testosterone alone, the University of Geneva team revealed not just a single answer, but new questions worth pursuing—and new tools to pursue them with.