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Marijuana Smoking May Be Linked With Having Higher Sperm Counts

Adapted from Marijuana smoking and markers of testicular function among men from a fertility centre published in February 2019 issue of Human Reproduction.

Previous studies on the effects of marijuana on the reproductive system suggested that smoking marijuana reduces sperm count and has a negative effect on testicular function, but most of those studies had focused on animal models or a small group of people.

A new study from Harvard University found that men who have smoked marijuana at some point in their life had significantly higher concentrations of sperm when compared with men who have never used marijuana.

In this study, the researchers tested 662 men who were enrolled at the Massachusetts General Hospital Fertility Center between 2000 and 2017. From the pool, they collected 1,143 semen samples.

The 365 men (55%) who reported having smoked marijuana had significantly higher sperm concentration: 63 million sperm per milliliter of semen — compared to the 297 nonsmokers, which averaged 45 million/mL.

There were no significant differences in sperm counts between current and former marijuana smokers. Interestingly, each additional year that had passed since a man last used marijuana was tied to a slight increase in sperm count. Among marijuana smokers, researchers also found that heavier marijuana use was linked to higher sex hormone testosterone levels.

The study raises the possibility that marijuana use could affect sperm production via a neurotransmitter system in the body known as the endocannabinoid system.

The researchers emphasized that they do not know to what extent these findings may apply to men in the general population as the study population consisted of men in couples seeking treatment at a fertility center.

The cause and effect remain to be determined. It could be that the numbers reflect "reverse causation." That is, men with higher testosterone levels are more likely to use marijuana — perhaps in part because they're more willing to take risks — and men with higher testosterone levels also tend to have higher sperm counts.

In conclusion, it is important to remember that the study findings do not necessarily mean that smoking marijuana increases the chance of fathering a baby.

March 2019


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