Cannabis appears to do a fair bit of damage to sperm health, and new research even suggests that this could impact the development of future children. Understandably, these findings raise many questions for prospective parents and aspiring fathers.
Does smoking weed really cause male infertility? Here, we delve into what the scientists are saying about cannabis and sperm health.
How cannabis exposure affects sperm health
With the growing legalisation of cannabis across the globe, researchers are able to better assess its effects on a large population. In recent years, numerous studies have highlighted a link between regular cannabis use and reduced sperm health which could, in turn, negatively impact male fertility.
One 2019 review, published in the Journal of Urology, analysed the results of 48 studies and determined that “research supports a role for cannabis in reducing sperm count and concentration.” More specifically, one particular study of 1,215 young men between the ages of 18 and 28 years found that regularly smoking cannabis (more than once a week) was associated with 28% lower sperm concentration and a 29% lower total sperm count.
There is also mounting evidence to suggest that cannabis can cause abnormal sperm morphology. Altering the size and shape of sperm can negatively impact their motility, making them poorer swimmers and hindering their ability to penetrate an egg.
The detrimental effects of cannabis on sperm can be attributed to the plant’s mind-altering cannabinoid, THC (or tetrahydrocannabinol). Research suggests that THC competes with endocannabinoids at cannabinoid receptors, altering the signalling mechanisms within sperm and subsequently impairing their function.
However, the existing evidence is far from conclusive, and there is even conflicting data surrounding the effects of cannabis on sperm. For instance, some research has shown that men who have smoked cannabis throughout their life have a higher sperm count and sperm concentration.
In one study, cannabis users had an average sperm concentration of 62.7 million/ml of ejaculate, whereas non-users had 45.4 million. Only 5% of cannabis users had sperm concentrations that were considered to be below the normal level and even showed higher blood testosterone levels – a hormonal predictor of male fertility.
Whilst the latter study has some limitations with its methodology, it certainly highlights that the link between cannabis use and sperm health is less clear-cut previously anticipated, emphasising the need for more rigorous research – both experimentally and clinically – into the effects of cannabis on male fertility.
Could cannabis influence evolution?
Animal model research has shown that short-term, high-dose exposure to cannabis vapour not only lowers sperm count and motility in male mice but also in their offspring. This suggests that cannabis use may also have an epigenetic influence, disrupting DNA in the sperm cell which is then passed on to a second generation.
Epigenetic modifications are changes to gene activity that are caused by our behaviour and environment. Yes, that’s right; the way you live your life can alter your DNA – or, more specifically, how your body reads a DNA sequence. Since epigenetic changes can be inherited they can, in turn, influence evolution.
In the context of cannabis, researchers have noted DNA methylation (an epigenetic change) in the sperm of rats after exposure to THC. Another study found that the offspring of rats exhibited a disruption in their neurobehavioural development after paternal exposure to THC.
Whilst no studies have investigated whether the two are linked – that being, whether the DNA methylation caused the behavioural changes – some researchers believe they are. What’s more, new research highlights a similar association between cannabis and epigenetics in humans.
A study, published in Epigenetics in 2020, found that cannabis use is associated with the disruption of an autism candidate gene in human sperm. Whilst these findings are concerning, the data mustn’t be misconstrued. This is preliminary evidence from a single study that used a very small sample size and should not be falsely interpreted as, “cannabis causes autism”. There is currently no evidence to suggest that the link is causative. Instead, the results simply highlight an association and call for further research on the matter.
Concerns over cannabis and conception: to the dads-to-be
For any readers who hope to become a dad in the future, here’s what you need to know. Reassuringly, studies have shown that refraining from cannabis use diminishes these epigenetic modifications in sperm within 77 days, suggesting that avoiding cannabis when trying to conceive reduces the risk of these aforementioned neurodevelopmental changes.
Dr Jamin Barhmbhatt, a urologist specialising in chronic testicular pain and infertility, recommends stopping cannabis use when trying to conceive to maximise fertility. Barhmbatt told The IVF Center that several of his male infertility patients “…stopped their marijuana use for a couple [of] months and everything went back to normal without any medications, without any manipulation, or any surgical intervention.”
Since alcohol and nicotine have been shown to have comparable damaging effects on sperm, it is standard advice for couples to go sober when trying to conceive, and it looks as though “Cali-sober” isn’t included in this guidance.
Having said that, population studies appear not to mirror the fertility effects seen in animal models in the lab. One study, published in Fertility and Sterility in 2018, found that men and women who use cannabis while trying to conceive, even daily, don’t take any longer to get pregnant than non-users.
Although far more research is needed to verify the animal model findings, it seems as though smoking a bit of weed may not be as catastrophic to your sperm health as some studies suggest. Cannabis doesn’t render your swimmers useless, but it’s safe to say that they’d probably be healthier without it.