New research led by Harvard T.H. Chan School of Public Health, concludes that adult men who have smoked pot at some point in their lives have substantially higher concentrations of sperm when compared with men who have never consumed cannabis. According to the study, "Marijuana smoking and markers of testicular function among men from a fertility center,” conducted in the Fertility Clinic at Massachusetts General Hospital, there is no significant difference in sperm concentrations between current and former marijuana smokers.

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The terminology surrounding the swimmers is as follows: Semen, which contains sperm, is merely the fluid discharged during orgasm, often referred to as “seminal fluid.” The sperm cells in semen – the tiny tadpole-like cells shown in a typical sex-ed class animation– are what penetrate and fertilize egg cells, according to Inhale MD. “These unexpected findings highlight how little we know about the reproductive health effects of marijuana, and in fact of the health effects of marijuana in general,” said Jorge Chavarro, Associate Professor of Nutrition and Epidemiology at Harvard Chan School.

The Results Prove More Research is Needed

human sperm and egg cell 3d illustration iStock / koya791
Postdoctoral Research Fellow at Harvard Chan School, Ms. Feiby L. Nassan is the lead author of the study. Additional Harvard Chan School study authors included Ms. Mariel Arvizu, Research Scientist Dr. Lidia Mínguez-Alarcón, Senior Lecturer on Biostatistics Director of Graduate Studies, Biostatistics, Paige Williams, and Dr. Russ Hauser. Professor Chavarro advises that the results "need to be interpreted with caution, and they highlight the need to study the health effects of marijuana use further."

A prior study of Danish men in 2015, by T.D. Gundersen et al., entitled, Association Between Use of Marijuana and Male Reproductive Hormones and Semen Quality: A Study Among 1,215 Healthy Young Men, found that men who regularly smoked marijuana more than once per week had significantly lower sperm counts, but significantly higher serum testosterone concentrations.

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The current study, published on February 5, 2019, in Human Reproduction, states, “To further evaluate the role of marijuana on male reproductive function, we studied the association between self-reported marijuana smoking and markers of testicular function as measured by semen quality parameters, sperm DNA fragmentation, and serum reproductive hormones.

Based on the preponderance of previous findings, we hypothesized that marijuana smoking would be associated with worse semen quality and lower serum testosterone.” According to the UN Office on Drugs and Crime (UNODC), in 2015 approximately 183 million people report using marijuana, making it the most commonly used drug worldwide. On average, 16.5% of adults in the U.S. use marijuana, (19.4% in men and 13.6% in women) while enthusiasm for legal adult use of marijuana is increasing rapidly, both across the United States and abroad.

Interpreting the Study

Understanding the health effects associated with marijuana use is essential given the contradictory perception that using marijuana lowers male sperm count. According to the study, the researchers hypothesized that marijuana smoking associates with poor semen quality. Previous related studies suggest that adverse effects on male reproductive health correlate to cannabis use.

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However, the majority of those studies focused on men with histories of drug use, or animal models. For this generational study, between 2000 and 2017 researchers amassed 1,143 semen samples from 662 participants, whose average age was 36 years old. Many (88%) were Caucasian, held college degrees (84%), and did not currently smoke cigarettes (94%).

Additionally, 317 of the men underwent a blood sample analysis, to measure their reproductive hormone levels. “Use of marijuana and other drugs was self-reported at baseline. Standard protocols were followed for measuring semen quality, sex hormones, and DNA integrity. We used linear mixed effect models with a random intercept to evaluate the associations of self-reported marijuana smoking at enrolment with semen parameters from subsequently collected samples, and linear regression models for sperm DNA integrity and serum reproductive hormones, while adjusting for confounders including smoking and cocaine use,” the study explains.

To gather information on marijuana use among study participants, researchers used a self-reported survey that asked the men numerous questions about their cannabis usage. The poll asked if they had ever smoked more than the equivalent of two joints worth of marijuana in their lives; and if they were currently active cannabis consumers.

Of the contributors, 365, or 55%, reported having smoked marijuana at some point in their lives. Of those, 11% classified themselves as current smokers, while 44% said they were past marijuana smokers. The pot smokers were “more likely to be white, overweight and tobacco smokers” as well. They also had higher consumption rates of alcohol, coffee and “were more likely to have ever used cocaine.”  

Liquid nitrogen cryogenic tank at life sciences laboratory iStock / anamejia18
An analysis of the semen samples showed that men who claimed that they have never smoked marijuana have average levels of 45.4 million sperm per milliliter of ejaculate, whereas evaluees who admitted they have smoked weed have average sperm concentrations of 62.7 million sperm per milliliter of ejaculate.

The World Health Organization’s (WHO) threshold for “normal” levels is 15 million/mL. Only 5% of pot smokers had sperm concentrations below that, compared with 12% of men who said they have never smoked marijuana. Interestingly, the study also found that among cannabis consumers, greater usage correlates to higher serum testosterone levels.

Potentially Flawed Data

The researchers caution that there are several potential loopholes in their conclusions, such as the participants may have downplayed their marijuana use, due to its illegality during the course of the study.   Additionally, the researchers emphasize that their findings are preliminary because they are unaware to what extent these findings may apply to men outside the scope of the research. The control group consisted of subfertile men who were seeking treatment at a fertility center.

The researchers acknowledge that there are few similar studies in which to compare their findings. “Our findings were contrary to what we initially hypothesized. However, they are consistent with two different interpretations. The first being that low levels of marijuana use could benefit sperm production because of its effect on the endocannabinoid system, which is known to play a role in fertility.

However, those benefits are lost with higher levels of marijuana consumption,” said Nassan. "An equally plausible interpretation is that our findings could reflect the fact that men with higher testosterone levels are more likely to engage in risk-seeking behaviors, including smoking marijuana,” said Nassan.