Nausea, headaches, and breast pain are all common side effects of hormone therapy, reports MedicineNet.com. Additionally, hormone therapy is shown to increase risk for vein clots in the legs, blood clots in the lungs, breast and uterine cancer, and heart attacks.
Women undergoing hormone therapy are two to three times more likely to develop deep vein thrombosis and pulmonary embolus, according to MedicineNet.com. Estrogen supplementation without progestin also causes elevated risk of endometrial cancer in women with intact uteri. In a similar fashion, hormone therapy poses a slightly increased risk of breast cancer: eight additional cases of breast cancer were found per 10,000 women taking hormone therapy for one year versus women taking a placebo. Although hormone therapy can positively affect cholesterol levels, women undergoing therapy are not protected from heart disease and actually have an increased risk of heart attack.
Other documented complications of hormone therapy are abnormal vaginal bleeding and increased risk of stroke, states MedicineNet.com. Depending on the therapy used, postmenopausal women can expect some bleeding every month with cyclic doses, or irregular bleeding for up to a year if daily doses are administered. As was found with breast cancer, eight additional strokes were reported per 10,000 women undergoing hormone therapy for one year versus women taking a placebo.