For instance, in his 2019 review, Dr. Pastuszak and several colleagues reported that cannabis use was strongly associated with lower sperm counts and concentration, as well as a higher incidence of abnormally shaped sperm.

The following year, a study of 229 Jamaican men showed that even moderate cannabis use was associated with a nearly three and a half times greater likelihood of misshapen sperm, which lowers the odds for a successful fertilization.

In addition, a new study of 113 Jordanian men found that sperm movement, called motility, was far lower in cannabis users than among tobacco smokers and nonsmokers, said Dr. Mohamed Eid Hammadeh, whose lab at Saarland University in Germany conducted the study. After THC bound to the sperm’s cannabinoid receptors, they found, it proceeded to damage the mitochondria inside the cell.