 The levels of 20α-DHD, which is the main active metabolite, are also found to peak about 1.5 hours post-dose.A single intramuscular injection of 100 mg dydrogesterone in microcrystalline aqueous suspension has been found to have a duration of action of 16 to 38 days in terms of clinical biological effect in the uterus in women.This was specifically the time until the onset of withdrawal bleeding in estrogen-treated amenorrheic women.