The result was a big surprise for scientists who measured from couples attending a fertility clinic, the sperm counts hundreds of men (more than 600).
They expected cannabis to impact sperm count and fertility negatively. Instead, participants who admitted to having already taken the drug were found to have a higher sperm count than non-users.
A surprising Harvard study!
The authors of the study and other experts did not hesitate to point out that smoking cannabis does not necessarily increase the chances of being a father.
There may be a non-causal explanation for this association, such as the effect of the male hormone testosterone on sperm count and risky behaviors such as cannabis use.
Previous research involving experiments on animals or men with a history of drug abuse has suggested that cannabis harms the reproductive health of men.
For the new study, scientists collected from 662 men between 2000 and 2017 1,143 semen samples.
The average age of the men was 36 years old, most of them white and college educated. All belonged to couples seeking a fertility clinic to help them with conception.
The researchers asked participants to complete questionnaires detailing their history of cannabis use.
More than half (55%) of men reported smoking cannabis at some point. Of these, 44% reported having used drugs in the past, and 11% were among current users.
Influence of cannabis on testosterone
Analysis of semen samples showed that men who had smoked marijuana, on average, had a concentration of 62.7 million sperm per milliliter on average. For those who had never smoked a joint had an average of 45.4 million sperm/mL.
Only 5% of cannabis users had sperm counts below 15 million sperm/mL, the World Health Organization’s threshold for “normal” levels, compared to 12% of men who had never smoked cannabis.
However, the study concluded that increased cannabis use was associated with higher levels of testosterone, a male hormone, among smokers.
In the journal Human Reproduction, scientists said that it was possible that low exposure to cannabis could be beneficial for sperm production in one way or another.
The endocannabinoid chemical messenger system in the brain, which is targeted by the drug, is known to play a role in regulating fertility.
On the other hand, the association may have nothing to do with the effects of cannabis.
Two different interpretations: the first being that low levels of cannabis use could be beneficial for sperm production because of its effect on the endocannabinoid system, which is known to play a role in fertility, but these benefits are lost when cannabis use increases.