Marijuana has a similar effect on sperm as it does users, a new study has found.
Too much weed can reduce men's fertility, and it turns out that's because it makes sperm "mellow" and fond of "swimming in circles", rather than their towards their destination.
"The weight of the evidence is that marijuana probably has a negative impact not only for sperm counts but sperm function," said Dr Victor Chow, of the University of British Columbia.
The good news is cutting back on the dope should see sperm recover quite quickly - men's entire stash is renewed every three months.
Even using just once a week can reduce sperm count and make the sperm act strange, Dr Chow's research found.