Synthetic estrogens have numerous uses in medicine. The most common and notable use of estrogens is as birth control pills or contraceptives and as hormone replacement therapy.

Estrogen as part of oral contraceptives

Estrogen in blood sends negative feedback to the brain and reduces secretion of Follicle Stimulating hormone (FSH) and Luteinizing hormone (LH). In this manner it can prevent ovulation or release of the ovum from the ovary.

Even in men, the major hormone involved in LH feedback is estradiol, not testosterone. Most oral contraceptives contain a synthetic estrogen, along with a synthetic progestin.

Birth control pills (also called oral contraceptives or hormonal contraceptives) are the most commonly used form of birth control in the United States. The pills may contain a combination of estrogen and progestin or contain progestin alone.

Most women take low-dose birth control pills, which have 50 micrograms or less of estrogen. Modern birth control pills contain 20 to 50 micrograms of estrogen.

Earlier birth control pills contained larger amounts of estrogen. This raised the risk of stroke, heart attack, and blood clots in the lungs as well as long term effects like breast cancer. Now low dose estrogen pills are commonly used.

Estrogens in hormone replacement therapy (HRT)

Estrogens and other hormones are given to postmenopausal women in order to prevent osteoporosis as well as treat the symptoms of menopause. These symptoms include:

• hot flashes
• vaginal dryness
• urinary stress incontinence
• chilly sensations
• dizziness
• fatigue
• irritability
• sweating

It has been seen that postmenopausal women are susceptible to bone disorders, brittle bones and risk of fractures. Fractures of the spine, wrist, and hips decrease by 50-70% and spinal bone density increases by ~5% in those women treated with estrogen within 3 years of the onset of menopause and for 5–10 years thereafter.

In addition HRT has favorable effects on serum cholesterol levels. This leads to the hypothesis that when initiated immediately upon menopause may reduce the incidence of cardiovascular disease or heart disease and atherosclerosis. Estrogen appears to have a protector effect on atherosclerosis: it lowers LDL and triglycerides, it raises HDL levels and also increases blood vessel dilatation and anti-inflammatory activities.

Earlier standard therapy was 0.625 mg/day of conjugated equine estrogens (such as Premarin). After risks associated with conjugated equine estrogen therapy were found that included dangerous blood clotting, newer dosages and regimens are adopted.
Other uses

Estrogen vaginal creams have been used to decrease vaginal dryness after menopause. Estrogens have also been seen to promote wound healing.

Some researchers have found use for estrogen in bulimia nervosa, traumatic liver injury etc. Under certain circumstances, estrogen may also be used in males for treatment of prostate cancer.