A study published in the American Journal of Epidemiology looked at 1,215 healthy young men and the association between the use of cannabis and their reproductive hormones and semen quality. The study found that regular cannabis consumption more than once per week was associated with a 28% drop. Combined with other drugs or medicine and the sperm count dropped 55%.
The authors of the study conceded that “we cannot exclude the possibility that the men who used marijuana generally have an unhealthier lifestyle and health behavior, which may also affect their semen quality and hormone levels.”
But this wasn’t the first study to find a correlation between sperm-related issues and cannabis. A piece in the journal Human Reproduction noted that cannabis may affect sperm’s size and shape, and a 2004 in The Journal of Clinical Endocrinology & Metabolism stated that “cannabinoids and endocannabinoids negatively influence sperm functions.”
Those who disagree about the correlation often point to famous consumers, like Willie Nelson, who has fathered seven kids.