- On average, men who had ever smoked marijuana had a higher sperm concentration, higher sperm count and lower concentration of follicle-stimulating hormone (FSH) than men who had never smoked marijuana
- More intense use of marijuana was associated with significantly higher average concentrations of testosterone, sex hormone–binding globulin and inhibin B
- These results are consistent with a direct pro-spermatogenic testicular effect and secondary compensation in FSH secretion
- Each additional year since last smoking marijuana was associated with a higher sperm count, greater sperm DNA integrity and lower concentration of estradiol
Only a few studies of the health effects of marijuana have focused on how it influences the reproductive system. What's more, for men this research has focused on subjects with a history of drug abuse, which limits the generalizability of the results.
To address the knowledge gap, a team of researchers from the Environment and Reproductive Health (EARTH) Study, including John Petrozza, MD, director of the Mass General Fertility Center, fertility specialist Jill Attaman, MD, and Russ Hauser, MD, chair of the Department of Environmental Health at Harvard T.H. Chan School of Public Health, studied men undergoing fertility services. To their surprise, they found that marijuana smoking does not impair sperm count, sperm concentration or serum concentrations of reproductive hormones—and might actually improve them.
In Human Reproduction, the researchers report that they analyzed 662 men who contributed 1,143 semen samples and 317 serum samples from couples presenting to the Fertility Center between 2000 and 2017. The average age was 36 years. Most men were white, had a university degree and did not currently smoke tobacco.
55% of the men had smoked marijuana at least once in their lives—44% were past and 11% were current marijuana smokers. The researchers note that these percentages closely match the frequency of marijuana smoking in the general U.S. population.
Results for the Overall Population
Compared with men who had never smoked marijuana, men who had ever smoked it had a significantly higher sperm concentration in a multivariable-adjusted analysis. There were no significant differences in sperm concentration between current and past marijuana smokers. The patterns were similar for total sperm count.
Ever-smokers of marijuana had significantly lower serum concentrations of follicle-stimulating hormone (FSH) than never-smokers, again with no significant differences between past and current smokers.
Marijuana smoking status was not associated with any marker of sperm DNA integrity, any other semen parameter or concentrations of any other reproductive hormone.
Results for Marijuana Smokers
The research team then restricted their analyses to men who had ever smoked marijuana:
- More intense use (increased smoking by 20 joint-years) was associated with significantly higher serum concentrations of testosterone, inhibin B and sex hormone–binding globulin, as well as non-significantly higher sperm concentration and total sperm count
- Later age at initiation of marijuana smoking was associated with a non-significantly lower sperm count and concentration
Interpreting the Findings
These results are consistent with a direct prospermatogenic testicular effect of marijuana smoking and secondary compensation in FSH secretion, the researchers conclude. They consider three possible explanations:
- The associations could be spurious. Not all findings fit the picture of a positive effect of marijuana on testicular function. For example, sperm concentration and total sperm count were better for past marijuana smokers than for current smokers, even though the differences were not significant. Moreover, each additional year since last smoking marijuana was associated with a higher sperm count, greater sperm DNA integrity and lower concentration of estradiol
- The findings could reflect reverse causation. Prior research has shown that men with higher circulating testosterone concentrations are more likely to engage in risk-seeking behaviors, including marijuana and cocaine use, and that testosterone is positively related to sperm count. The data available in this study did not allow the researchers to determine whether reverse causation explains their findings
- The findings could reflect a true biological association. The researchers note that the effect of marijuana smoking on spermatogenesis and hormone production was dose-dependent and non-linear. Their current working hypothesis is that moderate marijuana use is related to improved testicular function, and the adverse reproductive effects shown in animal and human studies are attributable to greater intensity of marijuana use
The research team calls for additional research into the effects of marijuana smoking on male fertility.
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