“Δ(9)-Tetrahydrocannabinol (Δ(9)-THC), a biologically active constituent of marijuana, possesses a wide variety of pharmacological and toxicological effects (e.g., analgesia, hypotension, reduction of inflammation, and anti-cancer effects).

Among Δ(9)-THC’s biological activities, its recognized anti-estrogenic activity has been the subject of investigations.

… Δ(9)-THC is used as both a drug of abuse (marijuana) and as a preventive therapeutic to treat pain and nausea in cancer patients undergoing chemotherapy…

…important to investigate the mechanistic basis underlying the anti-estrogenic activity of Δ(9)-THC…

We have recently reported that ERβ, a second type of ER, is involved in the Δ(9)-THC abrogation of E2/ERα-mediated transcriptional activity. Here we discuss the possible mechanism(s) of the Δ(9)-THC-mediated disruption of E2/ERα signaling by presenting our recent findings as well.”

http://www.ncbi.nlm.nih.gov/pubmed/25177025