The precise ovulation-inhibiting dosage of MGA is unknown. However, doses of 1 to 5 mg MGA were previously used in combined birth control pills in combination with the estrogen ethinylestradiol or mestranol. MGA is an effective contraceptive by itself at dosages of 0.35 to 0.5 mg/day, but is not effective at a dosage of 0.25 mg/day. MGA alone does not inhibit ovulation at a dosage of 0.5 mg/day, nor does it fully inhibit ovulation at a dosage of 0.7 mg/day or even at a dosage of 5 mg/day. The combination of 2 to 5 mg/day MGA and 100 μg/day mestranol has been found to consistently inhibit ovulation, whereas either medication alone did not completely inhibit ovulation in all women.