The effects of cannabis on the hormonal system and male fertility remain controversial within the scientific community. A study conducted by the University of Geneva (UNIGE), in collaboration with the Swiss Center for Applied Human Toxicology (SCAHT), provides a new answer by showing that cannabis use does not reduce testosterone levels in young men and may even increase its testicular synthesis. However, this increase in hormone levels cannot be directly linked to fertility. These conclusions are based on a detailed analysis of plasma samples from 94 Swiss conscripts. In addition, the researchers identified two new hormonal biomarkers that may help detect regular cannabis use. The findings have been published in Communications Medicine.

Some studies suggest that cannabis may reduce sperm count, concentration, and motility. These effects are believed to be linked to the endocannabinoid system—a network of chemical messengers and receptors in the brain and reproductive organs that interacts with sex hormones. However, the findings of studies conducted so far — particularly regarding the impact of cannabis use on testosterone — have often been contradictory.

To investigate further, a team from the Section of Pharmaceutical Sciences at the UNIGE Faculty of Science, led by Professor Serge Rudaz and in collaboration with SCAHT, conducted an in-depth analysis of steroid hormones — including sex hormones such as androgens, progestogens, and estrogens — in blood plasma samples from Swiss conscripts aged 18 to 23. The cohort included 47 confirmed cannabis users and 47 non-users. The major innovation of this study lies in extending the analysis to hundreds of hormones, whereas previous research focused solely on testosterone.

Increase in Testosterone

“Our results show that cannabis use would lead to an increase of about 23% in testosterone in young men,’’ explains Serge Rudaz. ‘‘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. Androgens produced by the adrenal glands were not affected by this increase.’’ Cannabis therefore appears to have a direct effect on the testes, and more specifically on Leydig cells, which produce testosterone.

Thanks to this broader analysis, the team was also able to identify two potential new biomarkers of cannabis use: hydroxyprogesterone (11B-OHP4) and dihydroprogesterone (5B-DHP4). “These are two metabolites derived from progesterone, another important sex hormone. The increase in their concentration among users is so high that they could be used to monitor endocrine disruptions linked to regular cannabis exposure. Above all, this discovery should encourage the scientific community to expand studies to new hormones that have so far been overlooked, and which may also play a role in the male reproductive system,” explains Mathieu Galmiche, a former postdoctoral researcher in the UNIGE Section of Pharmaceutical Sciences, now at the Karolinska Institutet in Stockholm and the study’s first author.

No Link to Sperm Quality

However, this increase in hormone levels among cannabis users should not be interpreted as an indicator of sperm quality. The link between testosterone and fertility remains very complex to decipher. Furthermore, the observed increase could represent a compensatory response by the body to reduced sensitivity of certain androgen receptors in the presence of cannabis. It is also possible that men with naturally higher testosterone levels are more prone to risk-taking behavior and, consequently, more likely to use cannabis.

While cannabis appears to affect certain biological mechanisms related to reproduction, the exact clinical implications for the fertility of young men remain unclear. Further research is needed to determine whether a toxicity threshold exists and to assess potential long-term effects.