Men who had smoked marijuana had more concentrated sperm than men who had never smoked marijuana, the researchers found. Sperm concentration was almost 63 million per milliliter for men who had smoked versus only about 45 million per milliliter for those had never smoked, the team reports today in the journal Human Reproduction.
When Dr. Jorge Chavarro's team started investigating marijuana's effects on sperm, they had every reason to believe weed would prove detrimental to "testicular function", because other studies had said it to be so.
Here's where it gets interesting: The men who'd smoked marijuana at any point ever had average sperm concentrations of 62.7 million sperm per milliliter of ejaculate, while the men who'd never smoked had an average of only 45.4 million/ml.
However the authors wrote that their findings may not relate to the general population, and said their study was limited by the fact they relied on the men reporting their use of cannabis accurately.
"We spent a good two months redoing everything, making sure that there wasn't any error in the data", Cahvarro was quoted by Bloomberg.
But a new study of more than 600 males suggests that a little cannabis use may not actually be so bad for dudes' reproductive health: In fact, study participants who had smoked marijuana at some point in their lives had significantly higher sperm concentrations than those who'd never used the drug.
Past studies have claimed that using the drug could lower a man's sperm count.
The participants in the new study self-reported their marijuana use, so the details they gave may not have been accurate.
It is estimated that 16.5% of adults in the US use marijuana, and support for legal recreational use of marijuana has increased dramatically in recent years.
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Nassan also said that the results may have been skewed by cannabis prohibition.
The findings appear in the journal Human Reproduction.
Researchers analysed health surveys from men who sought fertility treatment at the Massachusetts General Hospital Fertility Center between 2000 and 2017. Those who smoked marijuana in the past but don't now partake are more likely to have a higher sperm count than those who do.
There were no significant differences in sperm concentrations between current and past marijuana smokers.
Out of those who reported to have been using bhang, only 5% had sperm counts below 15 million/ml, the threshold for normal levels as per the World Health Organisation. About half of the men in the sample had also gotten a blood test, allowing the researchers to look at their levels of hormones such as testosterone.
For now, there's just not enough evidence to make any conclusions about the use of marijuana on male sperm.
Professor Sheena Lewis from Queen's University Belfast said: 'In studies from our lab in Queens University, Belfast, we found exactly the opposite effects. "However, they are consistent with two different interpretations, the first being that low levels of marijuana use could benefit sperm production because of its effect on the endocannabinoid system, which is known to play a role in fertility, but those benefits are lost with higher levels of marijuana consumption", commented Feiby Nassan, lead author of the study.
Whether smoking marijuana affects sperm quality and quantity or not is a controversial topic, he said, and too few studies have been conducted to provide a concrete answer.