• General term for the female hormones (including oestradiol, oestrone, oestriol) produced in the ovaries (and in small amounts in the testes and adrenals). In women oestrogen is important in the menstrual cycle and in the development of secondary sex characteristics (e.g., breast development in adolescence).
• As a synthetic preparation, sold under many trade names, oestrogen drugs are used to treat menstrual irregularities, to relieve symptoms of menopause, to treat cancer of the prostate, and in oral contraceptives.

Long-term use of oestrogen has been associated with some blood-clotting disorders and some forms of cancer and is controversial.