Premarin is the commercial name for a medication consisting primarily of conjugated estrogens. Isolated from mares’ urine (pregnant mares’ urine), it is manufactured by Wyeth Pharmaceuticals (part of Pfizer since January 2009) and has been marketed since 1942. It is available in oral (0.3/0.45/0.625/0.9/1.25 mg), IV, and topical (vaginal) form.