The result came as a big surprise to scientists measuring the fertility of more than 600 men from couples attending a clinic.
Examining more than a thousand semen samples from 662 men between 2000 and 2017, the researchers found something unexpected.
Out of the group of participants, 55 percent reported having smoked marijuana at some point. "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". However, Chavarro said his team's paper "does not mean that using more marijuana is going to increase sperm counts, or testosterone or your masculinity".
Dr Jorge Chavarro said the findings were unexpected - and highlight how little is known "about the reproductive health effects of marijuana, and in fact the health effects of marijuana in general".
However, the authors also advised caution when interpreting the findings, saying that the study does have limitations including the possibility of participants underreporting marijuana use because of its illegality during much of the period, as well as highlighting that it's unclear how much the results would extend to the general male population.More news: Rockets Acquire Iman Shumpert, Kings Get Alec Burks In Three-Way Trade
More news: Crude Oil Price Lower But Remains Range Bound
More news: Ontario health inspections, air ambulance won't be privatized, minister says
The men who admitted to smoking marijuana at some point in their life seemed to have higher concentrations of sperm than those who had never had a puff.
Previous studies showed excessive smoking cannabis reduced sperm counts and testosterone levels. Along with their medical history, the men were also asked if they had ever used cannabis and, if they had, whether they were still using it. Allan Pacey, professor of andrology at the University of Sheffield, U.K., authored a 2014 study suggesting that using cannabis can impact the size and shape of sperm, and in turn male fertility.
Feiby Nassan, lead author of the study and a postdoctoral research fellow at Harvard Chan School, told Newsweek: "Because the endocannabinoid receptors (the ones responsive to marijuana) are found in many places in the body especially the reproductive system, we need to understand their role on our health, especially with increasing their legalization".
And rightfully so. In 2015, a study published in the American Journal of Epidemiology examined 1,215 healthy young men and found that those who used recreational marijuana a few times per week had lower sperm counts than those who used the substance less often or not at all.
Other experts in the field have questioned how robust the association is. Another reason, according to the researchers, is that men may be more likely to engage in "risk-seeing activities", like smoking marijuana, if they have higher testosterone concentrations- something that aids in fertility. The men in the study reported smoking an average of two joints per week.
Only 5% of cannabis users had sperm counts below 15 million/mL, the World Health Organisation's threshold for "normal" levels, compared with 12% of men who had never smoked cannabis.