A weak estrogen, which needs to be converted (in target tissues such as the endometrium) to the strong estrogen estradiol before, as a hormone, it causes an estrogen effect. The main estrogen in blood after the menopause. Formed from estradiol when that hormone in tablet (or oral) forms is absorbed across the intestines. Abbreviated E1.

The general name for one of the two principal female sex hormones (the other is progesterone), responsible for stimulating growth of the female reproductive system (the vagina, the cervix, the uterus and the fallopian tubes) and growth of the breasts. The main estrogen is estradiol, produced by: the developing follicle (and to a lesser extent by the corpus luteum) in the ovary; by the trophoblast of the placenta; and by the body's fat tissues (through conversion from male sex hormones, or androgens, in the blood). After the menopause the main estrogen is the weaker one, estrone, largely derived from conversion by the body's fat of the weak androgen androstenedione.

Orally effective form of estradiol that resists being converted to estrone after ingestion. Generic ('no frills') name for Estigyn and Progynon C.

A mixture of estrogens in tablet form (from Ayerst Laboratories) with the reputation of being 'natural', though in reality extracted from the serum of pregnant mares (horses); the main human estrogen it contains is estrone.