Common side effects of conjugated estrogens include headache, abdominal pain, nervousness, nausea, back pain, joint pain and vaginal bleeding. Patients may also experience vaginal spotting, loss of periods or excessively prolonged periods, breast pain, breast enlargement and an increase or decrease in sexual drive.
Effects of estrogen on the skin include rash, and melasma (tan or brown patches) that may develop on the forehead, cheeks, or temples and may persist even after estrogens are stopped. In the eyes, conjugated estrogens may cause an increase in the curvature of the cornea, and, as a result, patients with contact lenses may develop intolerance to their lenses.
Estrogens may increase calcium levels in the blood (hypercalcemia) in patients with breast and bone cancer. Some patients may experience increased blood pressure and triglyceride levels.