In short
Hormone replacement therapy (HRT) refers to prescription treatment with hormones — most commonly estrogen, often combined with progestogen — to replace levels that decline naturally with menopause or other endocrine changes.
Menopausal HRT is prescribed to treat symptoms of estrogen decline, including hot flashes, night sweats, vaginal atrophy, and sleep disruption, and is also used specifically to prevent osteoporosis in appropriate candidates. Formulations vary by hormone type, dose, route (oral, transdermal patch, gel, or vaginal), and whether progestogen is included (progestogen is added for anyone with a uterus, to protect against endometrial cancer risk from unopposed estrogen).
The field was significantly reshaped by the Women's Health Initiative (WHI), a large U.S. randomized controlled trial whose initial 2002 results — showing increased breast cancer, stroke, and blood clot risk in the combined estrogen-progestin arm — led to a sharp global drop in HRT prescribing. Subsequent re-analyses have substantially refined that picture: risk varies significantly by the age at which HRT is started and years since menopause, with more favorable risk profiles in women starting HRT within 10 years of menopause onset (the “timing hypothesis”), and risk differing between estrogen-only and combined regimens, and by route of administration.
Current guidance from bodies including The Menopause Society (formerly NAMS) supports HRT as an appropriate, evidence-based option for symptomatic women, particularly under age 60 or within 10 years of menopause, individualized based on personal and family risk factors — a meaningfully different message than the blanket avoidance that followed the initial 2002 WHI headlines. HRT for general longevity or anti-aging purposes in the absence of menopausal symptoms or bone-loss risk is a separate, off-label use with a much thinner evidence base than the symptom-treatment indication.