Published: Thu, February 07, 2019
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Men who have smoked weed have higher sperm concentrations

Men who have smoked weed have higher sperm concentrations

In December 2018, INSIDER reported on a small study from Duke University that suggested marijuana use could be linked to lower sperm concentrations, a factor that can affect a man's fertility. What's more, all the of the men were enrolled at a fertility clinic, meaning they were seeking medical help with their partners to try to get pregnant.

Just five per cent of marijuana smokers had sperm concentrations below 15 million/mL, the World Health Organization's threshold for "normal" levels, compared with 12 per cent of men who had never smoked pot.

One explanation is that the men in the study who smoked marijuana already had higher sperm counts than those who did not. Now, researchers at Harvard have found an unexpected side effect of smoking pot - it appears to increase sperm count.

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".

"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", said study author Jorge Chavarro, "Our results need to be interpreted with caution and they highlight the need to further study the health effects of marijuana use".

For the new study, researchers collected 1,143 semen samples from 662 men between the years 2000 and 2017. On average, the subjects were 36 years old, white and college educated. For example, in 2015, researchers from Denmark found that men who smoked marijuana a few times per week had sperm counts that were almost 30 percent lower than those who didn't smoke marijuana, or those who used the drug less frequently. However, the new study showed that men who smoked weed had an average sperm concentration of 62.7 million sperm per millilitre (million/mL). That's a lot.

Those who had never smoked a joint had an average count of 45.4 million/mL.

Men who have a history of smoking cannabis have higher sperm counts and fertility than those who don't.

Among men who had ever smoked marijuana, those who used it more often had higher testosterone levels than those who used it less often.


Scientists found there was no significant difference in sperm concentrations between current and former smokers.

The endocannabinoid chemical messenger system in the brain, which is stimulated when cannabis is in the body, can play a role regulating fertility.

On the other hand the association could have nothing to do with the effects of cannabis.

"Our findings were contrary to what we hypothesized at the start of the study", study lead author Feiby Nassan, a postdoctoral research fellow at the Harvard T.H. Chan School of Public Health, said in the statement.

This view was echoed by leading British expert Allan Pacey, Professor of Andrology at the University of Sheffield. 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.

Chavarro also went on to point out that if the study proves anything definitive, it is that the link between marijuana and general health remains something of a grey area.

In subjects, each taking the same moderate dose of marijuana daily over only several weeks, their sperm quality plummeted.

This is because higher sperm count may not necessarily have anything to do with cannabis.

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