Hormone replacement therapy (HRT), also known as menopausal hormone therapy or postmenopausal hormone therapy, is a form of hormone therapy used to treat symptoms associated with female menopause. These symptoms can include hot flashes, vaginal atrophy, accelerated skin aging, vaginal dryness, decreased muscle mass, sexual dysfunction, and bone loss. They are in large part related to the diminished levels of sex hormones that occur during menopause.Estrogens and progestogens are the main hormone drugs used in HRT. Progesterone is the main female sex hormone that occurs naturally and is also manufactured into a drug that is used in menopausal hormone therapy. Although both classes of hormones can have symptomatic benefit, progestogen is specifically added to estrogen regimens when the uterus is present to avoid the increased risk of endometrial cancer. Unopposed estrogen therapy promotes endometrial hyperplasia and increases the risk of cancer, while progestogen reduces this risk. Androgens like testosterone are sometimes used as well. HRT is available through a variety of different routes.The long-term effects of HRT on most organ systems vary by age and time since the last physiological exposure to hormones, and there can be large differences in individual regimens, factors which have made analyzing effects difficult.
It was recognized in the early 1980s that the addition of a progestogen to estrogen reduced this risk to the endometrium. This led to the development of combined estrogen–progestogen therapy, most commonly with a combination of conjugated equine estrogen (Premarin) and medroxyprogesterone (Provera). Trials
The Womens Health Initiative trials were conducted between 1991 and 2006 and were the first large, double-blind, placebo-controlled clinical trials of HRT in healthy women. Their results were both positive and negative, suggesting that during the time of hormone therapy itself, there are increases in invasive breast cancer, stroke and lung clots. Other risks include increased endometrial cancer, gallbladder disease, and urinary incontinence, while benefits include decreased hip fractures, decreased incidence of diabetes, and improvement of vasomotor symptoms. There is also an increased risk of dementia with HRT in women over 65, though at younger ages it appears to be neuroprotective. After the cessation of HRT, the WHI continued to observe its participants, and found that most of these risks and benefits dissipated, though some elevation in breast cancer risk did persist. Other studies have also suggested an increased risk of ovarian cancer.The arm of the WHI receiving combined estrogen and progestin therapy was closed prematurely in 2002 by its Data Monitoring Committee (DMC) due to perceived health risks, though this occurred a full year after the data suggesting increased risk became manifest. In 2004, the arm of the WHI in which post-hysterectomy patients were being treated with estrogen alone was also closed by the DMC.