The research, conducted by Harvard University scientists, were looking into whether smoking cannabis has a significant link to a male’s sperm count. Researchers measured the sperm counts of more than 600 men in order to study the negative effects of cannabis on male fertility. However, they were shocked to find that those who smoked the drug – even if it was only once – had a higher fertility rate than those who did not.
But the experts said smoking marijuana does not help increase fertility in men, and that there was still more to learn about the cause-effect relationship of the drug.
Lead researcher Dr Jorge Chavarro, from the Harvard TH Chan School of Public Health in Boston, said: “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.
“Our results need to be interpreted with caution and they highlight the need to further study the health effects of marijuana use.”
The study, published in journal Human Reproduction, was based on 1,143 semen samples from 662 men between 2000 and 2017.
The men were on average 36-years-old, were mostly white and college educated, and belonged to couples facing fertility problems seeking help to conceive.
In total, 55 percent of the men admitted to trying cannabis at some point in their lives, while 44 percent said they were regular users in the past.
Meanwhile, 11 percent said they still smoked the drug.
The results showed that those who smoked marijuana had an average sperm concentration of 62.7 million sperm per millilitre (million/mL).
Those who never smoked cannabis had an average sperm count of 45.4 million/mL.
And five percent of men who smoked cannabis had a sperm count lower than 15 million/mL, compared to 12 percent of those who never once smoked a joint.
A sperm count of 15 million/mL is the the World Health Organisation’s (WHO) threshold for “normal” levels.
Experts believe there may be a link between moderate cannabis use and how that can benefit the male’s reproductive system.
The endocannabinoid chemical messenger system in the brain, which is stimulated when cannabis is in the body, can play a role regulating fertility.
However, some researchers say that men with naturally higher testosterone levels are more likely to engage in risk-taking behaviours – meaning they are more likely to have tried cannabis.
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.”