Male marijuana users may produce more sperm than those who have never used the drug, according to the unexpected findings of a new study.
The research contradicts previous studies which have claimed that marijuana use may reduce sperm counts in men.
As such, the team of researchers from the Harvard T.H. Chan School of Public Health in Boston, whose work was published in the Feb. 6 issue of the journal Human Reproduction, are tentative with their conclusions and certainly do not advise men to start smoking cannabis to increase their fertility.
They say that more research is required to see whether smoking marijuana at specific levels could indeed have a beneficial effect on sperm production.
What is clear from the research is that it demonstrates how little is concretely known about the impact of marijuana use on reproductive health.
“We know a lot less than we think we know,” said senior study author Dr. Jorge Chavarro, an associate professor of nutrition and epidemiology.
Other studies on this question have found that smoking marijuana may lower a man’s sperm count, particularly among frequent and heavy users. One such study in 2015 by researchers in Denmark, suggested that men who smoked marijuana more than once per week had 30 percent lower sperm counts than those who did not smoke cannabis, or who did so less regularly.
But the impacts of more moderate cannabis consumption on sperm counts are less clear.
The latest study draws its results from 662 men who had their fertility, and that of their partners, evaluated from 2000 to 2017 at the Massachusetts General Hospital Fertility Center. In addition to providing sperm and blood samples, the men were asked how often they smoked marijuana or used other drugs.
Only 11 percent said that they currently smoked cannabis, but 55 percent responded that they had done so in their lifetimes.
The 55 percent who had smoked marijuana were found to have an average sperm concentration of 63 million sperm per milliliter of semen. Those who had never smoked marijuana reported 45 million sperm per milliliter of semen. The researchers took into account factors that could affect a man’s sperm count such as age, tobacco use, and alcohol consumption, but their findings still held.
Only 5 percent of current marijuana smokers had lower-than-average sperm concentrations (less than 15 million sperm per milliliter of semen) than would be expected, compared with 12 percent of those men who had never smoked cannabis.
“Our findings were contrary to what we hypothesized at the start of the study,” said lead study author Feiby Nassan, a postdoctoral research fellow at the Harvard T.H. Chan School of Public Health.
Though the findings are very much still open to interpretation, it could be the case that low or moderate consumption of marijuana has a beneficial impact on sperm production, which is then reversed by heavier usage.
Another possibility is that men with higher testosterone levels produce more sperm but are also more likely to take risks, such as by using drugs.
There are other issues with the research that it makes it even more difficult to draw firm conclusions about the relationship between marijuana use and male fertility.
The researchers note that the participants in the study are all men visiting a fertility clinic, meaning the sample is hardly representative of the general population. Also, the men in the study self-reported their marijuana use, and its possible that they may not have been entirely truthful or accurate given their interests in visiting the clinic, as well as the continuing social stigma and illegal status of the drug in Massachusetts at the time of the study.