What is an exogenous estrogen?
An endogenous estrogen is one that occurs naturally within the body. In contrast, an exogenous estrogen is one that comes from outside the body — from a drug or from foods with estrogen-like properties. The exogenous estrogens used in birth control pills and estrogen replacement therapy may be manufactured from natural or synthetic sources. In the United States, the most common form of replacement estrogen is a natural estrogen called conjugated equine estrone (e.g., Premarin) — “equine” because it is derived from the urine of pregnant mares. Some estrogen replacement drugs are made from plant estrogens (e.g., Ogen).