I was thinking of DHT, but I wasn't sure. I know progesterone can block the actions DHT, but I wasn't sure if they both compete against each other (to do vice versa). I do think I recall Winstrol possesing that ability now that you mention it.
The only other anti-
progesterone I know of is Mifepristone (RU-486), but it has
progestin activity of its own...