Smoking too much pot doesn’t just chill men out, it can cause their sperm to become “more mellow and swimming in circles.”
Just a couple of joints a week could be enough to lower sperm counts by almost a third, even when accounting for other lifestyle factors, recent research shows.
“The weight of the evidence is that marijuana does affect sperm counts,” said Dr. Victor Chow, a clinical associate professor at the University of British Columbia Medical School’s department of urological sciences.
While the occasional puff likely won’t cause too much harm, among “heavy users it will definitely affect the quality of the sperm,” he said.
Dr. Chow said some studies focus on lowered sperm counts, but marijuana also appears to affect sperm’s motility, or how it moves, and makes it “more mellow and swimming in circles.”
After a slew of headlines this summer about the decline in sperm counts and Western fertility, there has been much handwringing over lifestyle factors. And, with marijuana legalization pending in Canada, experts say it’s worth having a discussion about some of the side effects of heavier pot use.
“The weight of the evidence is that marijuana probably has a negative impact not only for sperm counts but sperm function,” Dr. Chow said.
The effect on male fertility is strong because “sperm is a very rapidly turning over cell,” he said. That means heavy marijuana use can have an immediate effect on sperm production because the male body makes new sperm about every three months.
Dr. Chow also noted that women who are trying to become pregnant shouldn’t use marijuana, just as they shouldn’t use other drugs.
Dr. Armand Zini, an associate professor of urology at McGill University who researches male infertility, said he would advise heavy marijuana users who are having trouble conceiving to cut back, given the growing breadth of evidence about the direct effect of pot use on sperm counts and quality. But he also cautioned we need more clinical studies to fully understand the effects.
“The science of it is not very strong, I have to say, because we don’t have that many clinical or experimental studies,” Dr. Zini said, adding that most are animal studies, although there have been several convincing ones involving humans. “Even though we may not have the strongest data on this, there’s some evidence to support what I am saying.”
Both doctors pointed to a massive 2015 study out of Denmark, where over 1,200 young men participated. It found: “Regular marijuana smoking more than once per week was associated with a 28-per-cent … lower sperm concentration and a 29-per-cent … lower total sperm count after adjustment for confounders (other factors like weight, smoking and time between the sample given and last ejaculation).”
While those researchers cautioned further research is required, the Danish team also noted, “Our findings are of public interest as marijuana use is common and may be contributing to recent reports of poor semen quality,” and cited the growing number of countries that are legalizing marijuana.
All this runs counter to what pot activists often like to frame as false “Reefer Madness”-style information about marijuana. In August, Jodie Emery, one of the owners of Cannabis Culture and a marijuana advocate, wondered on Twitter if it’s not time Health Canada removed lowered sperm count from its list of side effects.
Turns out, for even moderate users — the Denmark study found that people who used pot more than one a week were affected — cutting back on the ganja may be a good move if they’re trying to conceive.
And while many past studies have focused on THC — the main chemical in pot that gets you high — the effects of the complex cannabinoids contained in the drug also need to be considered.
Those complex drugs could actually hold some good news for men struggling with infertility. A 2016 study in the British Journal of Pharmacology found that a specific cannabinoid receptor could help trigger sperm production, and indicated that understanding how to do so could lead to a treatment for infertility.
The flip side, of course, is that triggering that receptor could also hinder production or quality if done irregularly or in a way that depresses instead of stimulates sperm count, so those researchers also cautioned not to take their study as a sign that pot is good for sperm production, but as another sign it definitely affects it, for better or worse.
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