Men who have smoked marijuana at some point in their life had significantly higher concentrations of sperm when compared with men who have never smoked marijuana, according to new research led by Harvard T.H. Chan School of Public Health. They also asked the men about past and present marijuana use, though they did not ask about specific dosages or frequency.
"An equally important limitation is the fact that most of the data were collected while cannabis was illegal in MA, so it is hard to know to what extent men may have under-reported use of cannabis because of social stigma or potential consequences related to insurance coverage for infertility services", he said.
Experts found that men who reported to have smoked marijuana had an average sperm concentration of 63 million sperm per milliliter of semen. This system sends signals to the brain and these signals may play a role in fertility, they explain.
Dr Feiby Nassan, another member of the Harvard team, said: "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 behaviours, including smoking marijuana".
On top of that, the average sperm count of cannabis consumers was much higher than the average for non-consumers.
In their study, they found that men who had smoked marijuana have an average of 62.7 million sperm per milliliter of ejaculate.
But the study does highlight how little researchers know about the effects of marijuana on reproductive health, study senior author Dr. Jorge Chavarro, an associate professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health in Boston, said in a statement. In December 2018, INSIDER reported on a small study from Duke University that suggested marijuana use could be linked to lower sperm concentrations, a factor that can affect a man's fertility.
Numerous older studies had focused on animal models or had examined men with histories of drug abuse. The authors of a study published in the journal Human Reproduction wrote of "a growing perception that marijuana poses few health hazards and with increased legalization and decriminalization of recreational marijuana use worldwide". Both of those numbers are still considered healthy; the World Health Organization's threshold for "normal" levels is all the way down at 15 million/ml.
In all, little over half of the men (55%) reported never smoking marijuana in their lifetimes, and 11 percent said they are a current user of cannabis and smoke regularly. Other research revealed marijuana use reduced sperm motility and ejaculate volume. Since marijuana was still illegal in MA at that time, it's possible that many test subjects under-reported or even lied about their cannabis consumption during the trial. It may be that low or moderate levels of marijuana use have a beneficial effect on sperm production, but heavier use reverses this effect.
Vij said she applauded the study authors for looking at this question, since it is a topic that needs more research. He also points out that semen quality is not necessarily a predictor of how easily or quickly a couple can get pregnant and that "these findings should not be interpreted as implying better fertility with cannabis use".
Whether those changes can be passed on to a child remains unknown, but for now, some researchers are warning that men in their childbearing years should consider how weed might impact their fertility and possibly their offspring.