Norethindrone is a synthetic progestin derived from 19-nortestosterone that is used medicinally in the treatment of menstrual disorders and endometriosis. More commonly, it is used as an oral contraceptive when combined with an estrogen. Norethindrone is available commercially by prescription by a host of trade names, including Aygestin®, Micronor®, Norlutate®, Norlutin®, and Nor-QD®, among other names, for reproductive disorders, and as Ortho-Novum®, Norlestrin®, Norinyl®, and Brevicon®, among other names, as oral contraceptives also containing an estrogenic substance, either mestranol or ethinyl estradiol. Laboratory animal studies have demonstrated masculinization of female offspring in six species. Norethindrone administration during pregnancy in humans has resulted in approximately 80 cases of masculinized female offspring and a small number of cases of hypospadias in male offspring. Norethindrone is a larger than average human developmental toxicant. It is hydrophobic and of low polarity. Norethindrone can engage within hydrogen bonding interactions.