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.
Chavarro and his team set out to study the possible effects of pot smoking on male reproduction by observing 662 men enrolled at the Massachusetts General Hospital Fertility Center in Boston between 2000 and 2017. "Higher testosterone levels are also related to slightly higher semen quality and sperm counts".
As the researchers hypothesised that marijuana smoking would be associated with poorer semen quality, they were surprised to find that men who had smoked marijuana at some point in their lives actually had a higher average sperm concentration - 62.7 million sperm per millilitre of ejaculate - than men who had never smoked, who had an average concentration of 45.4 million sperm per millilitre of ejaculate.
"There could be a non-causal explanation, such as the effect of the male hormone testosterone on both sperm count and risk-taking behaviour such as smoking cannabis", said U.S. lead researcher Dr Jorge Chavarro, from the Harvard TH Chan School of Public Health in Boston.
"We spent a good two months redoing everything, making sure that there wasn't any error in the data", Cahvarro was quoted by Bloomberg.
Researchers found participants who had smoked marijuana at least once had higher sperm concentration, counts, and lower FSH concentrations compared with those who had never used the drug.
Numerous older studies had focused on animal models or had examined men with histories of drug abuse. Now, researchers at Harvard have found an unexpected side effect of smoking pot - it appears to increase sperm count.
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"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". 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 is well-documented that within normal ranges, high testosterone levels are associated with greater engagement in risk-seeking behaviors, including drug use", Chavarro said.
Nassan also said that the results may have been skewed by cannabis prohibition.
According to the study, men who smoke weed have higher sperm count than those who do not.
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. There were no statistically significant differences in sperm concentration between current and past cannabis smokers. The researchers also collected blood samples from 317 participants for the objective of analyzing reproductive hormones.
"Our findings were contrary to what we hypothesized at the start of the study", study head author Feiby Nassan, a postdoctoral research partner at the Harvard T.H. Chan School of Public Health, claimed in the statement. "For example, as the authors point out, men with higher sperm concentrations are likely to have more testosterone in their bodies and thus may be more likely to smoke marijuana because simply they are willing to take more risks". First, participants were only asked about smoking marijuana, not consuming it in other forms, like an edible.