Past studies have claimed that using the drug could lower a man's sperm count. However, a new study by the Harvard T.H. Chan School of Public Health in Boston, involving more than 600 men had surprising results.
US lead researcher Dr Jorge Chavarro 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."
Cannabis Smoking. Credit: PA
The men included in the research - mostly white, educated, with an average age of 36 - were all part of couples seeking help with conception from the Massachusetts General Hospital Fertility Centre between 2000 and 2017, and most of the men had normal sperm counts.
The research showed 55 per cent of the men had tried cannabis in the past and 11 per cent said they were current users.
When Dr Chavarro compared all the surveys, he found the marijuana users had a common result of having a slightly higher sperm counts and concentration, compared to men who had never used it.
Although the findings are fascinating, the research doesn't conclude that smoking marijuana actually increases sperm count, the doctor said.
A Man Smoking Marijuana. Credit: PA
He went on to say that it is more likely that men with higher testosterone levels, who already tend to have a higher sperm count and concentration, are actually more likely to use cannabis.
Dr Chavarro said: "It is well-documented that within normal ranges, high testosterone levels are associated with greater engagement in risk-seeking behaviors, including drug use. Higher testosterone levels are also related to slightly higher semen quality and sperm counts."
He said studies in the past that suggest drug use lowers sperm count don't specify cannabis, and are usually an amalgamation of several drugs. His study also looked at the effects of other drugs on sperm count - cocaine use was found to be related to lowering sperm count.
Sperm Sample Testing. Credit: PA
Originally the study was to prove causation, but the doctor said it's actually shown that much more research into the drug is needed.
He said: "We could have found what we thought we were going to find, and maybe wouldn't have been as surprised and would have ended up writing a very different paper.
"But the fact that we showed the exact opposite forced us to look very, very deeply into the marijuana health effects literature. There is not that much.
"We are operating mostly on assumptions and good intentions and hunches."
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