Cannabis and Testosterone: A Swiss Study Challenges Conventional Wisdom

For decades, concerns about the impact of cannabis on male reproductive health have fueled debate among scientists. While some studies have suggested that cannabis use could harm fertility and reduce testosterone production, new research conducted by the University of Geneva (UNIGE) paints a more nuanced picture.

Published in Communications Medicine, this study found that young men who use cannabis have significantly higher levels of several key male sex hormones, including testosterone. However, the researchers note that these hormonal changes should not be interpreted as evidence that the cannabis improves fertility or reproductive health.

Ces résultats mettent plutôt en évidence la complexité de la relation entre le cannabis, les hormones et le système reproducteur masculin.

Focus on Cannabis and Male Hormones

The effects of cannabis on the endocrine system have long been a subject of controversy. Since the 1970s, studies examining the relationship between cannabis use and testosterone levels have yielded conflicting results, leaving scientists without a clear consensus.

To investigate this issue further, researchers from UNIGE and the Swiss Center for Applied Human Toxicology (SCAHT) analyzed blood samples from 94 Swiss conscripts aged 18 to 23. The cohort included 47 regular cannabis users and 47 non-users.

Unlike many previous studies, which focused almost exclusively on testosterone, the Swiss team conducted a comprehensive hormonal analysis, examining dozens of steroid hormones involved in reproductive function and endocrine regulation.

This approach has allowed researchers to gain a much broader understanding of how cannabis use can affect hormonal pathways in young men.

Testosterone levels were higher among cannabis users

The most striking finding of the study was the increase in androgen levels among cannabis users.

Researchers observed that cannabis users had circulating levels of testosterone that were approximately 23% higher than those of non-users. Two other important androgens, androstenedione, a precursor to testosterone, and dihydrotestosterone (DHT), one of the body’s most potent male sex hormones, were also significantly elevated.

“Our findings show that cannabis use leads to an increase in testosterone levels of about 23% in young men,” explained Serge Rudaz, a professor in the Department of Pharmaceutical Sciences at UNIGE.

It is important to note that this increase was not observed in all hormonal pathways. The researchers found no significant changes in the hormones produced primarily by the adrenal glands. This distinction suggests that cannabis may specifically affect hormone production in the testicles.

According to the study, the cannabinoids pourraient influencer l’activité des cellules de Leydig, the specialized cells responsible for synthesizing testosterone.

These findings also support the observations from several large-scale population studies conducted in the United States and Denmark over the past decade, which also reported higher testosterone levels among cannabis users.

Overall, these findings increasingly call into question the long-held assumption that cannabis use necessarily inhibits testosterone production.

Why are testosterone levels higher?

While the hormonal differences seem clear, the underlying mechanisms remain unclear. One hypothesis is that cannabinoids interact directly with the endocannabinoid system of the body, a network of receptors and signaling molecules involved in the regulation of numerous physiological processes, including reproduction.

Cannabinoid receptors are present throughout the hypothalamic-pituitary-gonadal axis, the hormonal system that regulates reproductive function. They are also found in the testicles themselves, particularly in Leydig cells.

Researchers therefore believe that cannabinoids may directly affect testosterone synthesis, although the study did not determine exactly how this process occurs.

Another possible explanation is that the increase in testosterone represents a compensatory response. If exposure to cannabinoids reduces the sensitivity of androgen receptors, the body may increase hormone production to maintain normal biological function.

Researchers also acknowledge the possibility of a reverse causal relationship. Men who naturally have higher testosterone levels may be more inclined to engage in risky behaviors and therefore more likely to use cannabis in the first place.

Because the study was observational rather than experimental, it does not allow us to determine which explanation is correct.

Higher testosterone levels do not necessarily mean increased fertility

One of the most important takeaways from this research is that high testosterone levels should not be interpreted as evidence of improved fertility. The relationship between hormone levels and reproductive health is far more complex.

Previous studies have reported associations between cannabis use and a decrease in the number, sperm concentration, motility, and viability. Other studies, however, have found little or no impact on sperm quality.

The scientific literature therefore remains divided.

The Swiss researchers note that their findings provide insights into hormone production rather than reproductive outcomes. Although cannabis users had higher levels of testosterone and other androgens, the study did not determine whether these hormonal changes resulted in positive or negative effects on fertility.

In fact, some data suggest that cannabis may interfere with the biological processes involved in sperm function, even when testosterone levels remain normal or high.

As a result, researchers say that further research is needed before conclusions can be drawn about the broader implications of cannabis use on reproduction.

Identification of new biomarkers

Beyond testosterone, the study a également mis en évidence deux hormones susceptibles de devenir des biomarqueurs utiles de l’exposition au cannabis.

These compounds, known as 11β-hydroxyprogesterone (11β-OHP4) and 5β-dihydroprogesterone (5β-DHP4), were detected at significantly higher levels in cannabis users than in non-users.

Researchers believe that these hormones could help scientists monitor the endocrine disruptions associated with cannabis use.

The study also found that 11β-OHP4 appears to serve as a general marker of cannabis exposure, while 5β-DHP4 may also reflect the intensity of use. Levels of 5β-DHP4 were significantly higher among chronic users than among occasional users.

“Above all, this finding should encourage the scientific community to expand its research to include new hormones—which have been overlooked until now—that may also play a role in the male reproductive system,” said Mathieu Galmiche, the study’s lead author.

A rapidly expanding field of research

Although these findings provide valuable new data, the authors caution against overinterpreting the results. The study focused only on young Swiss men and reflects relatively recent exposure to cannabis. It does not provide information on long-term effects, older populations, women, or former users.

Lifestyle factors, such as diet, sleep, stress levels, and alcohol consumption, can also influence hormone production and could not be fully controlled.