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expert reaction to study on cannabis and sperm count

Reactions to research published in Human Reproduction that states men who had ever smoked marijuana had high sperm concentration and count than men who had never smoked marijuana.

Prof Sheena Lewis, Emeritus Professor of Reproductive Medicine, Queen’s University Belfast, said:

“In studies from our lab in Queens University, Belfast, we found exactly the opposite effects. In subjects, each taking the same moderate dose of marijuana daily over only several weeks, their sperm quality plummeted. Sperm motility decreased, acrosome reactions failed to occur and worst of all, sperm counts dropped and the nurse (Sertoli) cells that help to make sperm disappeared irreversibly.

“I would urge caution in accepting the findings of this study, without further information. Despite its large numbers and authorship from a highly esteemed university, it has several major design flaws: we do not know the baseline of sperm counts before marijuana smoking; making the reported increase less reliable. Secondly, the levels of marijuana taken were just self-reported so are open to high variation. Thirdly, recreational drug users often take cocktails of drugs. Another commonly used recreational drug that impacts on sperm is Viagra. We have reported that Viagra can improve sperm function. Perhaps multi-drug use accounts for these unexpected results.”

Dr Lindsey A. Hines, Sir Henry Wellcome Postdoctoral Fellow, Centre for Academic Mental Health, University of Bristol, said:

“This study finds that smoking moderate amounts of cannabis is linked to a higher sperm count in men visiting a fertility clinic. When interpreting these findings, it’s important to remember that we can’t tell if cannabis is causing a higher sperm count, as no measures of sperm count were taken before the men had started using cannabis.

“The authors say that these findings may not generalise to the general population. This is true – these men were recruited when attending a fertility clinic with their partners, so we can assume that they are having trouble conceiving, or fertility issues. What these results tell us is that men who are attending fertility treatment and who have smoked cannabis have a higher sperm count than other men having fertility issues. If the cannabis-smoking men in this study were compared to men in the general population, we may not see these results.”

Prof. Allan Pacey, Professor of Andrology at the University of Sheffield, said:

“Whether or not smoking marijuana has an effect on the quality or quantity of men’s sperm (and therefore potentially their fertility) is currently controversial. There have been too few studies to examine this systematically and moreover the difficulties in doing so (given that marijuana is an illegal drug in many countries) makes the design of appropriate studies more challenging.

“Unfortunately, in my opinion, this paper does not help us to get any closer to the truth. For example, the observation that men in this study who had ever (but not currently) smoked marijuana had a higher sperm concentration compared to those who had never done so is intriguing. But, critically, this does not demonstrate cause and effect. For example, as the authors point out, men with higher sperm concentrations are likely to have more testosterone in their bodies and thus may be more likely to smoke marijuana because simply they are willing to take more risks.

“We also don’t know exactly when the men in this study were asked to disclose information about their marijuana smoking habits and whether this was before or after they knew the results of their semen analysis. This is important because if the men were aware of their sperm quality when they were asked to complete the questionnaire, there is a danger that those with higher sperm counts may have “bigged up” their drug taking in order to have appeared more macho. Whereas men with poor sperm may have wanted to keep quiet about it so as to avoid any accusations of poor health behaviour.

“In the Chemicals and Pregnancy and Study (CHAPS-UK) I was part of a few years ago, we went to great lengths to avoid this kind of recall bias by asking men to complete all questionnaires before they found out the results of their semen analysis. We showed that in almost 2,500 men (i.e. much bigger than this new study) that smoking marijuana was not related to the number of motile sperm men ejaculated (i.e. quantity) but was related to sperm morphology (i.e. quality), with men who smoked marijuana more likely to have greater numbers of abnormally shaped sperm. Interestingly, this paper does not cite our two previous studies and nor do they cite the recent paper by Murphy et al., (2018) that was widely reported and showed that cannabis users had lower sperm concentrations and were more likely to have epigenetic defects in their sperm.

“In 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.”

‘Marijuana smoking and markers of testicular function among men from a fertility centre’ by Nassan et al. was published in Human Reproduction at 00:05 UK time on Wednesday 6th February.

All our previous output on this subject can be seen at this weblink:

Declared interests:

Prof Sheena Lewis: “Sheena is CEO of SpermComet Ltd, a university spin-out company marketing a test for male infertility.”

Dr Lindsey A. Hines: “I have no conflicts of interest to declare.”

Prof. Allan Pacey: “Chairman of the advisory committee of the UK National External Quality Assurance Schemes in Andrology, Editor in Chief of Human Fertility and Trustee of the Progress Educational Trust (all unpaid).  Also, recent work for the World Health Organisation, British Broadcasting Corporation, Purple Orchid Pharma (paid consultancy with all monies going to University of Sheffield).  Co-applicant on a research grant from the Medical Research Council (ref: MR/M010473/1).”

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