The estrogenicity of delta-9-tetrahydrocannabinol (THC): THC neither blocks nor induces ovum implantation, nor does it effect uterine growth.

The estrogenicity of THC was assessed in three estrogen-sensitive systems. The drug did not block implantation when injected (s.c.) on Day 0 of pregnancy: on Day 6, 95% (3 mg/kg) and 86% (12 mg/kg) of the mice had embryos as did 96% (P greater than 0.1) of the controls; implantation occurred in only 9% (P less than 0.005) of mice treated similarly with estradiol (E2; 0.15 mg/kg). Nor did THC induce implantation: pregnant mice were ovariectomized on Day 1, treated daily with progesterone (2 mg, s.c.) and injected (i.p.) with THC on Day 3: at mg THC/kg 39% had embryos, as did 41% of those at 6 mg/kg; these rates do not differ (P greater than 0.99) from that of the controls (38%); in contrast, ova implanted in 75% (P less than 0.025) of E2-treated mice (4.0 microgram/kg). The average number of implanting ova was the same in all groups in both experiments. THC did not cause uterine hypertrophy: ovariectomized mice were injected (s.c.) for 14 days with THC (3 or 6 mg/kg) or E2(2 microgram/kg): the uterine weight, total uterine protein and total uterine glycogen of the ovariectomized controls was 24 +/- 2 mg, 3 +/- 0.3 mg and 11 +/- 3 mg respectively and the values for the THC-treated mice were not different (P greater than 0.05); in contrast, E2 increased (P less than 0.01) uterine weight to 139 +/- 9 mg, uterine protein to 5 +/- 0.6 mg and uterine glycogen to 62 +/- 8 mg. It is concluded that THC is not estrogenic.