Antifertility properties of two non-oestrogenic steroids and MRL 37

Three antioestrogenic compounds showing no oestrogenic activity by vaginal smear tests at high dosages in mice exhibit contrasting antifertility actions. The steroid, SAP 104, which has no other known actions but antioestrogenicity, prevents mating but not pregnancy if given after mating. Another steroid, U-10997, prevents mating, also prevents pregnancy if given after mating and acts maximally during days 1–3 after mating. It is androgenic and anabolic. The non-steroidal MRL 37 does not prevent mating in doses up to 1 mg/day, but at that dose prevents pregnancy, even if administration is stopped at mating. It is also effective when given after mating at a similar dosage level on days 1–3 or 4–6.