Scientists discover how smoking weed has unexpected impact on testosterone levels in young men

Scientists have found that smoking weed does not lower testosterone levels in young men - in fact, it appears to do the opposite.

A study by the University of Geneva, conducted in collaboration with the Swiss Centre for Applied Human Toxicology in Basel, examined the fertility impact of cannabis on a group of young Swiss men aged between 18 and 23.

The results, published in the journal Communications Medicine, were not what many might have expected.

The researchers analysed blood samples from 94 Swiss recruits between the ages of 18 and 23, said the university.

The blood samples were split between 47 cannabis users and 47 non-users, and found that testosterone levels were much higher in the cannabis-using group.

Speaking to USA & World Report News, senior researcher Serge Rudaz, a professor at the University of Geneva said: "Our results show that cannabis use would lead to an increase of about 23% in testosterone in young men."

The findings confirm the results of earlier large-scale studies from Denmark and the United States, which had also identified a link between cannabis use and higher testosterone levels, contradicting older and smaller studies that had pointed in the opposite direction.

Contrary to what many assumed, cannabis users in the study actually had significantly higher testosterone levels than non-users (Getty stock image)

Why does cannabis increase testosterone levels in young men?

According to the researchers, the increase appears to originate specifically in the testicles rather than the adrenal glands, where male sex hormones called androgens are also produced. Cannabis appears to have a direct effect on the Leydig cells in the testicles, the cells responsible for testosterone production, while leaving adrenal hormone production unaffected.

The authors have offered a couple of possible explanations.

The rise could be a compensatory reaction, with the body producing more testosterone in response to a reduced sensitivity of certain hormone receptors. Alternatively, men with naturally higher testosterone levels may simply be more predisposed to risk-taking behaviour, including cannabis use, in the first place.

Researchers analysed blood samples from 94 recruits, 47 cannabis users and 47 non-users, and found that testosterone levels were around 23% higher in the cannabis-using group (Getty stock image)

Does higher testosterone from cannabis mean better fertility?

Despite the headline figures, the researchers were keen to pump the brakes on any straightforward positive interpretation.

A higher testosterone reading does not automatically translate to better sperm quality or improved fertility, they warned, the relationship between the hormone and reproductive health is considerably more complex than that.

While cannabis does appear to influence certain biological mechanisms involved in reproduction, the exact clinical consequences for the fertility of young men remain unclear.

The team said further research is needed to properly assess any potential long-term effects.