Estrogens are a class of hormones produced in the ovaries, or made from other hormones in fat cells. There are three estrogens: estradiol, estratiol and estrone. These natural hormones work more efficiently compared to synthetic estrogens or, even worse, animal estrogens. The most common (though cruelly-produced) animal product is Conjugated Equine Estrogens (Premarin). The proper dose is titrated against the pituitary hormones of LH and FSH. These are prescription drugs, but soy products can act as a surrogate for estrogen. Although estrogen may be good for men, according to studies, it is generally recommended only to women. Using estrogen alone in women, with their uterus still present, could, in a few percent, cause cancer of that organ.