For this study, the team compared semen samples of four groups of guys: 125 were infertile, 144 smoked tobacco, 74 used marijuana, and 279 guys didn't have any testicular health risk factors. Guys who smoked weed had higher levels of reactive oxygen species (ROS) in their sperm compared to cigarette smokers, according to the findings. This is concerning because too many ROS molecules may cause cell damage and possibly lead to infertility.

Weed consumption was also linked to abnormal sperm size and shape as well as decreased count and motility, or how well the cells can swim, according to the data . All of these are factors impacting male infertility.

"Overall, the marijuana group had semen quality equivalent to the infertile group, with the exception of higher ROS and DNA damage than infertile men," study co-author Jorge Hallak, MD, of the University of Sao Paulo explained to MedPageToday at the meeting. "DNA damage is higher in all groups (marijuana users, smokers, and infertile men) as compared to controls, but higher levels were found in the marijuana group and infertile men."

Earlier this year, a small study found that tetrahydrocannabinol (THC), the part of marijuana that gets you buzzed may change sperm DNA. Although researchers don't know if changes are permanent, one doctor told Men's Health guys should be very concerned about the findings.

So how do you make sperm thrive? The same factors that contribute to overall health , including exercise, eating a diet with plenty of fruits and vegetables, and a healthy body weight, can improve sperm quality.