NURSING MOTHERS: Estrogens are secreted in milk and cause unpredictable effects in the infant. Estrogens generally should not be used by women if they are breast-feeding.

SIDE EFFECTS: Among the most common endocrine side effects are break-through bleeding or spotting, loss of periods or excessively prolonged periods, breast pain, breast enlargement, and changes in sexuality (increase or decrease in libido). Abdominal pain may indicate the development of gallstones or occasionally hepatitis. Migraine headaches have been associated with estrogen therapy. Estrogens can cause sodium and fluid retention. Melasma, tan or brown patches, may develop on the forehead, cheeks, or temples. These may persist even after the estrogen is stopped. Conjugated estrogens may cause an increase in the curvature of the cornea. Patients with contact lenses may develop intolerance to their lenses.

Blood clots are an occasional but serious adverse effect and are dose-related. (The higher the dose, the more likely the clots.) Cigarette smokers are at a higher risk for clots, and, therefore, patients requiring estrogen therapy are strongly encouraged to quit smoking.

Estrogens can promote a buildup of the uterine lining (endometrial hyperplasia) and increase the risk of endometrial carcinoma. At diagnosis, endometrial cancers in estrogen recipients are generally of an earlier stage and a lower grade. Survival is also is better in women exposed to estrogens than in those not exposed to estrogens. The addition of a progestin to estrogen therapy prevents endometrial carcinoma.

Conflicting data exists on the association between estrogens and breast cancer. There may be a small increase in risk. The effect of concomitant progestin therapy on the risk of estrogen-induced breast carcinoma is unclear.

Reference: FDA Prescribing Information

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