Researchers have found that chronic exposure to doses of THC consistent with regular recreational or medicinal use results in dose-response testicular atrophy, increased serum gonadotropin levels, and decreased serum sex steroids in rhesus macaques. The study involved six male rhesus macaques aged 8 to 10 years who were given THC over the course of 210 days. Dosages began at 0.5 mg/7 kg/day. For a 68-kg man, this would translate into a 5 mg dose. The dosage was then increased to 1 mg/7 kg/day after 70 days. After another 70 days, the dosage was increased to 2.5 mg/7 kg/day.
The mean baseline weight of the animals was 11.6 kg and had increased to 11.9 kg (a 2.6% increase) during the high dosage period. More significantly, the average total bilateral testicular volume decreased by 12.6 cm3 for reach 1 mg/7 kg/ day increase in THC, with an average total decrease of 58%. Serum follicle-stimulating hormone, luteinizing hormone, and prolactin concentrations increased with each increasing 1 mg/7 kg/day by an average of 0.06 ng/mL, 0.16 ng/mL, and 7.4 ng/mL, respectively. A dose-dependent decrease in estradiol and testosterone was observed for each 1 mg/7 kg/day. For estradiol, the average decrease was 3.8 pg/mL. For testosterone, the average decrease was 1.49 ng/mL. No clear changes to semen characteristics were observed.
According to the study’s authors, “The rise in [luteinizing hormone] and [follicle-stimulating hormone] with increased exposure to THC, coupled with decreased testosterone and [estradiol], suggests that primary testicular failure is the mechanism of hormonal dysregulation by THC.” They concluded that even moderate doses of chronic THC could have adverse impact on men's reproductive health.
The study was first published in Fertility and Sterility. See here.