There is no evidence that marijuana impairs male reproductive functioning.
The Jamaican and Costa Rican field studies detected no differences in hormone levels between marijuana users and non-users.In epidemiological surveys of marijuana users, no problems with fertility have emerged as important.
In 1974, researchers reported diminished testosterone, reduced sexual function and abnormal sperm cells in males identified as chronic marijuana users. 34 In a laboratory study, the same researchers reported an acute decrease in testosterone, but no chronic effect after nine weeks of smoking; they did not evaluate sperm volume or quality. 35 In other laboratory studies, researchers have been generally unable to replicate these findings, 36 although by administering very high THC doses – up to 20 cigarettes per day for 30 days – one study found a slight decrease in sperm concentrations. 37 In all studies, test results remained within normal ranges and probably would not have affected actual fertility.
Severe adverse consequences have also been produced in male laboratory animals, although only with extremely high daily THC doses. 38
More importantly, in both the human and animal laboratory studies, all observed changes were reversed once THC administration was halted.
The claim that marijuana impairs female reproductive functioning in humans has no support in the scientific literature.
There have been no epidemiological studies indicating diminished fertility in female users of marijuana, and a recent survey found no impact of chronic marijuana use on female sex hormones. 39Animal studies show hormonal changes and depressed ovulation following extremely high daily doses of THC. As occurs with males, these changes disappear once the experiment is completed. 40 In addition, when THC was administered to female monkeys for an entire year, they developed tolerance to its hormonal effects and normal cycles were reestablished. 41
Almost immediately following publication of the few studies showing a marijuana impact on reproductive hormones, warnings about marijuana’s potential impact on adolescent sexual development began to appear.
Other than one case report of a 16-year old marijuana smoker who had failed to progress to puberty, 42 there has been nothing to indicate that such a potential exists. In whatever other ways one might consider marijuana to be bad for adolescents, it does not retard their sexual development.
Delta‐9‐THC appears to have a modest reversible suppressive effect on sperm production in men, but there is no proof that it has a deleterious effect on male fertility.
“Marijuana has little evidence implicating it in fetal harm, unlike alcohol, cocaine or tobacco. Epidemiological studies have found no evident link between prenatal use of marijuana and birth defects.”