Bioidentical hormones were first used for menopausal symptom relief in the 1930s, after Canadian researcher James Collip developed a method to extract an orally active estrogen from the urine of pregnant women and marketed it as the active agent in a product called Emmenin. It was supplanted on the market when its manufacturer, Ayerst (later Wyeth Pharmaceuticals), began producing the more easily manufactured conjugated equine estrogens in 1941 under the brand name Premarin; by 1992, Premarin was the most widely prescribed drug in the United States.