Danazol

Danazol is an estrogen inhibitor and a mild androgen/anabolic agent, slowing estrogen production and slightly increasing testosterone. It’s derived from a form of synthetic testosterone.

It acts as both an anti estrogen and a GnRH suppressant. (https://www.drugbank.ca/drugs/DB01406) It reduces estrogen production in the ovaries.

Danazol has proven effective in treatment of both fibrocystic breasts and endometriosis. It sometimes causes breast atrophy, and due to it decreasing estrogen, I think it could be a effective breast growth blocker for those who want to masculine slightly and prevent further breast growth before starting testosterone. (‭http://www.sciencedirect.com/science/article/pii/S1658361211701512‬)