Estrogen

Estrogen (sometimes called "oestrogen") is a hormone secreted primarily by the ovaries (a female-only endocrine gland in the human body).

Estrogen is one of a group of steroid hormones that control female sexual development, both promoting the development and function of the female sex organs, and also the female secondary sexual characteristics - including breast development, for example.
Although estrogens are synthesized mainly by the ovaries, some small quantities of estrogen are also produced by the adrenal cortex, the testes, and the placenta. (Estrogen is present in males, but excessive production of estrogen in men can lead to feminization.)

The actions of the hormone estrogen include:

Control of female sexual development;

Promotion of the growth of female secondary sexual characteristics at puberty;

Stimulation of egg (ovum) production;

Preparation of the lining of the uterus for pregnancy;

In conjunction with progesterone, regulation of the growth and functioning of sex organs for sexual reproduction;

Estrogens are used in female oral contraceptives, to inhibit the production of ova.
Note that pharmaceutical products vary widely and should only be used as directed by qualified professionals.