Marijuana surprisingly linked to high sperm concentrations

There is an unusual positive link between marijuana smoking and fertility, according to a new study published on February 5, 2019 in Human Reproduction. In the study, men who ever smoked marijuana were found to have higher sperm concentrations and count than those who never did.

The study was conducted by researchers at Harvard T. H Chan School of Public Health. The lead investigator was Feiby Nassan, a Postdoctoral Research Fellow at both the Department of Environmental Health and Department of Nutrition.

The study was in clear contrast to previous studies on human and animal models that found that abuse of marijuana negatively impacted on spermatogenesis – the process of sperm formation – even though there were no data on the effects of moderate use of marijuana on spermatogenesis.

Marijuana, also known as Cannabis, is the most abused illegal drug globally. United Nations Office on Drugs and Crime (UNODC) reports in the World Drug Report 2018:

Cannabis remained by far the most widely consumed drug worldwide in 2016, with 192.2 million past-year users, corresponding to 3.9 per cent of the global population aged 15–64 years.

Cannabis use among young people Source:  World Drug Report 2018 (Booklet 3) p. 12 (UNODC)

The World Health Organisation also has this to say about marijuana:

Cannabis is by far the most widely cultivated, trafficked and abused illicit drug. Half of all drug seizures worldwide are cannabis seizures. The geographical spread of those seizures is also global, covering practically every country of the world. About 147 million people, 2.5% of the world population, consume cannabis (annual prevalence) compared with 0.2% consuming cocaine and 0.2% consuming opiates.

Despite the adverse effects of marijuana, it is worthy of note that there have been increasing calls for the legalisation of the use of recreational marijuana across countries of the world recently. Supporters argue that many benefits can be derived by taking this step.

And the calls may have been getting results with Uruguay taking the lead. Uruguay is the first country in the world to make recreational marijuana legal in 2013, followed by Canada in 2018.

Back to the study under consideration. It was conducted among 662 sub-fertile men who attended Massachusetts General Hospital Fertility Centre between 2000 and 2017.

Among the participants, 365, or 55%, reported having smoked marijuana at some point, 44% of whom said they were past marijuana smokers and 11% classified themselves as current smokers. A self-reported questionnaire was used to get these data. In all, the participants provided a total of 1143 sperm samples.

From the study, those who ever smoked marijuana had average sperm concentrations 62.7 million sperm per milliliter of ejaculate. Among men who had never smoked marijuana, average sperm concentrations of 45.4 million per milliliter of ejaculate were found.

Using WHO ‘normal’ minimum threshold of sperm concentrations of 15 million per milliliter of ejacuate, only just 5% of those who ever smoked marijuana had concentration levels below this threshold.

Contrariwise, 12% of those who never smoked had sperm concentration levels below the threshold. It is important to remember that these data were among the study participants.

Also, greater use of marijuana was associated with higher serum levels of testosterone – the male hormone. Relatedly, the same pattern was observed with total sperm count.

Study findings must be interpreted with caution

The researchers explained that there were other findings in the study after further analysis that were inconsistent with true biologic mechanism of causal linkage but rather points to possibility of a spurious association.

Spurious association in statistical parlance implies that, although two or more variables are correlated, these variables in actuality are not causally related. The true picture is that there is usually an unseen factor responsible for the observed association.

Thus, correlation analysis merely establishes that the variables under focus vary together, whereas causation concludes that one phenomenon is the cause of another – which is not so in this case.

Furthermore, there are some other limitations to the study according to the researchers. As it is, study findings cannot be extended to the general population because sub-fertile men already attending fertility clinic were used for the study.

There is no denying the fact that best efforts were made by the researchers to adjust for confounders – other possible factors that could be responsible for their findings. Nevertheless,  there were still some chances that there could be factors within this sub-fertile population group of men, that may not be present within a ‘healthy’ fertile population, that could have accounted for this association.

Interestingly, the researchers themselves acknowledged these shortcomings and advised that further studies were needed to clear certain grey areas of the study. Likewise, they also mentioned the possibility of underreporting of marijuana usage as a major limitation of the study.

Read their assertion: 

The most important limitation of the study is the possibility of underreporting of marijuana use given its status as an illegal drug during most of the study, its social stigma and potentials effects on insurance coverage for fertility services of disclosing this information. In addition, we did not have information about other forms of marijuana use other than marijuana smoking.

This is notwithstanding the fact that past studies have shown that self-reported use of marijuana highly correlated with blood and urinary levels of cannabinoids in users. Cannabinoids are active substances or chemicals isolated from marijuana.

Why would the possibility of under-reporting be a major limitation of the study? This is because some of those who answered that they never smoked may have actually abused marijuana. If this was so and they reported otherwise, then the data did not truly reflect their marijuana exposure.

Similarly, since the study only focused on marijuana smoking, it was also possible those who claimed ‘never smoked status’ , truly abused marijuana through other means, thus underestimating the true effects of marijuana on them.

Either way, in the event of underreporting,  it was likely then that the lower concentrations of sperm found among those who claimed to ‘never smoked status’ might actually have been a reflection of their abuse rather than their ‘never smoked status’ as captured by the study.

Also, the link between marijuana smoking and high testosterone concentration raises the question of order: which one came first – is it the smoking or the high testosterone concentration?

This is given the fact that increased testosterone levels have been found to be associated with ‘risk-seeking behaviours’. Therefore, could it be that it was the increased testosterone level that led to the ‘risk-seeking behaviour’ of marijuana smoking in the first instance? 

Stop! This article did not say that.

Did not say what? That you should start using marijuana, if you never smoked. Neither is it saying you should not quit, if you are already smoking marijuana. Nor is it saying that you should increase your use, if you are a current user. No!

The information provided herein is clear – more studies are needed to clarify some of the findings from the study on the link between smoking of marijuana and high sperm concentrations.

It means therefore that consumers of health information must refrain from misinterpreting the content of this article to mean that marijuana smoking will help them to boost their fertility. Such is a wrong thinking and could lead to a destroyed life in the end!

Please read the many effects of marijuana and stay healthy!

In the same vein, the conclusion of the researchers is clear on next steps. See it below:

Marijuana smokers had higher sperm concentration and sperm count…than never marijuana smokers. These findings are not consistent with a deleterious role of marijuana smoking on testicular function as initially hypothesised. The findings are equally consistent, however, with a no-causal interpretation.

Whether these findings are reflective of the previously described role of cannabinoids in spermatogenesis and dose-dependent effects of the activation of endocannabinoid receptors on testicular function or are, instead, reflective of a spurious association, requires further work.

Thus, findings from the study as presented in this article ARE NOT SUFFICIENT REASONS for you to indulge in use of marijuana, if you are reading this article. Be warned and stay safe please!

If you would like to read the full article on the study, please check it out here.

Samuel Abiona

Samuel Abiona

Samuel Abiona is a medical doctor by training and a writer by passion. Samuel holds a postgraduate degree in Public Health. He believes that communicating medical knowledge goes beyond writing technical reviews. Samuel thus uses his expertise in public health and health systems research to transmit technical information for both academic and general audience. Please email to contact this author directly or use the contact page and your information will be passed on to him.