Harvard Study: Marijuana Smoking Linked with Higher Sperm Concentrations

As marijuana use continues to become legal in many U.S. states, questions have begun to be raised – some merely more frequently and loudly than they have been in prior years, if not decades – about the potential health benefits of using the drug. And, naturally, about the possibility of negative effects.

Marijuana use, after all, has long been considered an option for those for whom no other medical remedy is available or who are undergoing treatment with adverse side effects. Many proponents of marijuana swear by its palliative effects; some claim that it helps their ability to focus.

Now, a new study from the Harvard T.H. Chan School of Public Health indicates that men who have at some point in their lives smoked marijuana showed substantially higher sperm concentrations when compared with males who’ve never used the drug.

The February 2019 study, published in the journal Human Reproduction, also determined that sperm concentrations between former and current marijuana smokers were not significantly different.

Can smoking weed be OK for fathers-to-be?

Before anyone takes the above statements as evidence that marijuana use does not negatively impact one’s fertility, stop and carefully consider the words of Jorge Navarro, associate professor of epidemiology and nutrition at Harvard Chan School, about the study: “Our results need to be interpreted with caution and they highlight the need to further study the health effects of marijuana use.”

According to a Harvard Chan School press release, the study involved 662 men who gave semen samples between 2000 and 2017. 365 subjects, or 55 per cent, said that they had smoked marijuana at some point in their lives. Of those men, 44 per cent reported that they had smoked marijuana in the past, while 11 per cent said that they were current marijuana smokers.

Analysis of the samples indicated that men who’d smoked marijuana had, on average, sperm concentrations around 62.7 million sperm per ejaculate. Men who’d never lit up a joint had concentrations of 45.4 million. Just 5 per cent of marijuana smokers logged concentrations below 15 million – the World Health Organization’s “normal” level.

Researchers were, as noted, quick to point out that their findings should be taken with caution: Some participants might not have been completely transparent about their marijuana use, since the drug is still outlawed by federal statutes; the findings can’t be applied to everyone, since the study included only men known to be “subfertile” and seeking fertility treatment; and, there are also few similar studies with which to compare results.

The wider scientific community’s response

As might be expected concerning a hot-button issue like marijuana use, reaction from many in the scientific community was swift.

Professor Sheena Lewis, from Queen's University Belfast, told The Independent newspaper of London that her laboratory had looked into the effects of cannabis use at around the same levels described by the Harvard researchers.

“Their sperm quality plummeted,” she said, adding, “Worst of all, sperm counts dropped and the nurse cells -- also known as sertoli -- that help to make sperm disappeared irreversibly.”

Dr. Lindsey A. Hines, Sir Henry Wellcome Postdoctoral Fellow, Centre for Academic Mental Health, University of Bristol, was quoted by the Science Media Centre (SMC) as noting that it is important to bear in mind that no measures of the men’s’ sperm counts were taken before they had started using cannabis. As a result, he said, “[W]e can’t tell if cannabis is causing a higher sperm count”.

And Professor Allan Pacey, Professor of Andrology at the University of Sheffield (and a member of Legacy’s advisory board), was quoted by the SMC as saying that, when it comes to marijuana smoking and sperm concentrations, the study did not show cause and effect. And that the men included in the study might have understandably distorted the nature of their marijuana use because it can’t currently be determined when the subjects were asked to disclose that information.

Pacey’s quoted conclusion: “I am not convinced that this paper moves us any further forward in this debate. Moreover, nor does it give support to any apparent fertility benefits of smoking marijuana. In my opinion, this should be avoided at all costs in any couples trying to start a family.”

Your best move

While the jury remains very much out on the effects of marijuana use on male fertility, Legacy clients can take proactive steps to protect their assets now. If the landscape changes in any appreciable way in this regard sometime down the road, there’s always the option to change one’s mind – without irreversible damage having been done.