Cannabis may have negative effects on sperm, review finds

Cannabis could negatively impact male fertility, found a systematic review of dozens of studies published in the Journal of Urology. While more research is needed to confirm many of the findings, the authors cautioned that doctors and cannabis users should consider cannabis use as a factor in infertility cases.

This certainly isn’t the first time researchers have noted that cannabis might be negatively impacting male fertility. The authors of this review point to numerous studies that suggest potential fertility issues for men who use cannabis. And researchers have noted that cannabinoid receptors (which allow the cannabinoids in cannabis to interact with different systems in the human body) are expressed on human sperm. Thus, we know it is mechanistically possible for marijuana to affect sperm.

Cannabis’ Impact on Sperm Quality

The authors searched for any studies related to cannabis and male fertility (published before May 18th 2018) and found 48 animal and human studies to include. They found that research suggests cannabis may have negative impacts on hormones, sexual ability and testicular size. But the strongest body of evidence points to a negative effect on semen.

The research reviewed in this study showed that cannabis use in animals or humans could lead to reduced sperm count and concentration in semen, morphological changes in sperm, reduced motility and viability, and decreased fertilizing capacity.

For example, one included study found that men who reported using cannabis “more than once per week had a 28% lower sperm concentration and a 29% lower sperm count than men who had never used marijuana.” Similar results were seen in other animal and human studies as well, and researchers suspect that cannabis use may decrease the production of new sperm, leading to the lower results.

Morphological Changes from Cannabis

Animal and human models also provide evidence suggesting that cannabis induces morphological changes in sperm. For example, one study found that men who used cannabis in the last three months and were younger than 30 were more likely to have abnormal sperm morphology. Importantly, researchers did note that genetic material was not impacted by these morphological changes.

Cannabis also seems to affect sperm motility, or its ability to move on its own. Studies have found decreased sperm motility after just four weeks of high-dose cannabis intake.

Researchers also found evidence that cannabis use could reduce sperm viability (how many sperm are alive vs. dead in semen), and interfere with its ability to fertilize an egg. All these issues could be big factors in increasing the likelihood of infertility.

In addition to these issues, animal studies suggested cannabis use may cause testicular atrophy and erectile dysfunction. But these studies need to be replicated with humans to verify that humans respond similarly to rats and mice in this respect.

Different Studies, Different Conclusions

Still, while this study paints a dire picture of cannabis’ effects on male fertility, the authors point out that much of the research presented is limited, and more studies are needed to confirm these findings, particularly those based on animal studies.

While there is a considerable body of previous research drawn on in this review study, there is also other research that doesn’t fit the same pattern. Take for example, a study on cannabis and conception which looked at couples trying to get pregnant, surveying both men and women about their cannabis habits and their progress getting pregnant. This study found that cannabis users were just as successful in conceiving as their non-cannabis using counterparts.

In a more recent study from 2019 of 662 subfertile men, researchers found that men who had smoked cannabis actually had higher sperm concentration and sperm count than those who had never used cannabis. As is often the case with cannabis and our health, more research is certainly needed.

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