The antiandrogenic effect of progesterone on the hamster flank organ.

Progesterone, topically applied, prevents the stimulation of the hamster flank organ by testosterone, but not by dihydrotestosterone. 5 alpha-Dihydroprogesterone does not prevent stimulation by either of the two androgenic hormones. Neither progesterone nor 5 alpha-dihydroprogesterone stimulate the flank organ to any extent. Implications on the use of progesterone in acne therapy are discussed.