3 Surprising Facts About How Smoking Weed Impacts Your Sperm

Does smoking weed lower your sperm count? We get this question, a lot. In short, possibly.

The scientific jury is still out since there just hasn’t been enough research conducted to definitively evaluate the effect of marijuana on male fertility. But those studies are happening and they’re shaking up what we know about marijuana’s health impacts.

Here are three facts about how marijuana impacts your sperm health:


The most rigorous study was conducted at the University of Copenhagen in 2015.  Those researchers looked at 1,215 young Danish men (ages 18-25), and found that those who regularly used marijuana (more than once a week) had a 28% lower sperm concentration than men who smoked less frequently or never.  And, the men who combined marijuana with other recreational drugs had 52% lower sperm concentrations.

Those are significant differences.  But the researchers pointed out that the marijuana users also reported increased use of alcohol, tobacco, and caffeine, along with more stress, risk of STDs, and other factors that have been tied to infertility. While their models account for these differences, there may be other factors influencing the sperm count difference than just marijuana use.  In other words, it could be the unhealthy lifestyle of a marijuana user – including the Doritos and brownies – and not just the drug itself.

However, a new study published in 2019 out of Harvard University actually found the opposite effect: out of 662 men evaluated, the 365 men who reported that they had smoked marijuana at some point in their life had a significantly higher sperm count than those who had not. It was a small study but this was a very surprising, and interesting, outcome. The lead researcher, Dr. Jorge Chavarro, summed up our knowledge on this topic quite well, saying “We know a lot less than we think we know.”Are you ready to test your sperm?


Research has also shown that THC (the active ingredient in marijuana that gives you the high) could negatively affect your sperm’s ability to swim and fertilize an egg.  But maybe not in the way that you would think. When THC binds to the sperm cell’s mitochondria (the cell’s energy source), the chemical can kick the sperm cell into overdrive and make the it start swimming much more vigorously than normal.

You may think “more vigorous” swimming sounds like a good thing, but it actually has a negative effect in this case.  Sperm have to swim a long way to get to the egg (it’s about 6 inches, which is a long trek considering sperm are only one thousandth of an inch long).  So, if the sperm are overly hyper from the get-go, they quickly lose steam and are not able to complete the journey.  Remember, for sperm it’s a marathon, not a sprint.

Lastly, even if the sperm DO reach the egg, THC might prevent them from releasing the enzymes necessary for successful fertilization.  Scientists at Queen’s University in Ireland treated sperm cells with THC is their lab and found that those sperm cells were more likely to not release necessary enzymes.


We’d be remiss if we didn’t mention studies have found that men who regularly use marijuana (once a week or more) are 2.5x more likely to develop testicular cancer.  Low sperm count can be symptomatic of testicular cancer, so these findings corroborate the research around marijuana’s influence on sperm count.

Again, the science hasn’t yet pinpointed that it’s the drug itself (rather than the less healthy lifestyle of marijuana users in general), but there are indications that smoking weed could be a contributing factor.

We’re not here to ruin your party.  Marijuana use, of course, has a lot of benefits, too.  But we want to highlight the research that has been done to help you make the right decisions for you and your family (or in this case maybe your family-to-be).

For many guys, fatherhood marks a transition into adulthood.  If you’re trying to start your family now, it may be the time to cut back or give up on the weed habit as part of your commitment to your health and fertility.  It’s probably not going to hurt. 

Be sure to take our Male Fertility Assessment Quiz to see if your recreational choices and other lifestyle factors that could be affecting your fertility.  Then start your 90 Day Challenge to maximize your sperm count and chances of conception.

  1. D. Gunderson et al, American Journal of Epidemiology 2015, 182(6): 473-481.
  2. M. Eisenberg, American Journal of Epidemiology 2015, 182(6): 482-484.
  3. B. Whan et al, Fertility and Sterility 2006, 85(3):653-60.
  4. Gurney et al, BMC Cancer 2015, 15:897.
  5. F. Nassan et al, Human Reproduction 2019