Hormone replacement therapy (HRT) for menopause has had a turbulent evidence history. A 2002 publication from the Women’s Health Initiative (WHI) triggered widespread discontinuation of HRT after reporting increased risks of breast cancer and cardiovascular disease. Subsequent reanalysis of that data, and a decade of additional research, revealed that those risks applied primarily to older women who started HRT more than 10 years after menopause. For women who start HRT within 10 years of menopause or before age 60, the current evidence supports a favorable benefit-risk profile for most.

The clinical conversation about HRT has shifted substantially, and what was once regarded as nearly uniformly risky is now considered appropriate and beneficial for a specific, large population of women.

What the WHI Actually Found, and Why It Was Misapplied

The WHI enrolled 161,000 women aged 50-79. The subset using combined estrogen-progestogen HRT had a mean age of 63, more than a decade past menopause. This population was older and had more pre-existing cardiovascular disease risk than the women who typically seek HRT for menopausal symptoms.

The increased breast cancer risk found (8 additional cases per 10,000 women per year) was real but small. The increased cardiovascular risk was concentrated in older women and likely reflected the “timing hypothesis”: estrogen is cardioprotective when arteries are still compliant (near menopause) but may be harmful when applied to already-atherosclerotic vessels years later.

A 2013 reanalysis published in the BMJ stratified WHI data by age at initiation and found that women who started HRT between ages 50-59 had lower all-cause mortality, lower cardiovascular mortality, and lower breast cancer mortality than those who started after 70.

What HRT Treats

Vasomotor symptoms (hot flashes, night sweats): HRT is the most effective treatment available, reducing hot flash frequency by 75% or more in most women. No other intervention, pharmacological or behavioral, approaches this efficacy. This is the primary indication for most women who use HRT.

Genitourinary syndrome of menopause (GSM): Vaginal atrophy, dryness, dyspareunia (painful sex), and urinary symptoms respond well to both systemic and topical estrogen. Topical vaginal estrogen is highly effective for GSM with minimal systemic absorption and is appropriate even for women with breast cancer history in most cases.

Sleep disruption: HRT improves sleep architecture by reducing nighttime hot flashes and through direct effects of estrogen and progesterone on sleep regulation. Progesterone specifically has sedating properties.

Mood and cognitive function: The period of highest mood vulnerability in the menopausal transition, characterized by rapid estrogen fluctuations, responds to HRT stabilization of estrogen levels. Cognitive changes in the menopausal transition often improve with HRT.

Bone density: Estrogen prevents postmenopausal bone loss and is the most effective pharmacological option for bone density maintenance in early menopause. The protective effect requires continued use, stopping HRT allows bone loss to resume.

Breast Cancer Risk: The Current Evidence

The breast cancer question is more nuanced than either “HRT causes breast cancer” or “HRT is safe.”

Estrogen-only HRT: Women without a uterus who take estrogen alone show no significant increase in breast cancer risk in most analyses, and some show a reduction in risk. The WHI estrogen-only arm reported fewer breast cancer cases in HRT users than in placebo.

Combined estrogen-progestogen HRT: The elevated breast cancer risk is associated primarily with combined preparations containing synthetic progestins (like medroxyprogesterone acetate used in the original WHI). The risk is approximately 1 additional breast cancer case per 200 women over 5 years, roughly equivalent to the risk associated with two glasses of wine per night or BMI above 30.

Micronized progesterone: Evidence from French and Danish cohort studies suggests that combined HRT using micronized progesterone (bioidentical, not synthetic progestin) does not increase breast cancer risk. This has led many menopause specialists to prefer micronized progesterone over synthetic progestins.

Routes of Administration and Their Implications

Oral estrogen: Passes through the liver, which raises SHBG and clotting factors. Associated with a small increase in venous thromboembolism (blood clot) risk.

Transdermal estrogen (patches, gels, sprays): Bypasses first-pass liver metabolism, does not significantly raise clotting factors, and is not associated with increased VTE risk. For women with cardiovascular risk factors or those who are overweight, transdermal estrogen is generally preferred.

Local (vaginal) estrogen: Minimal systemic absorption. Appropriate for GSM even in women with a history of breast cancer in most cases, discuss with an oncologist.

Who Is Not a Good Candidate for HRT

HRT is generally not recommended for:

  • Women with a history of estrogen-receptor positive breast cancer
  • Women with a history of deep vein thrombosis or pulmonary embolism who would use oral estrogen (transdermal is not contraindicated in most cases)
  • Women with unexplained vaginal bleeding

For information on perimenopause specifically and what hormonal changes occur before menopause, see Perimenopause Symptoms: What Changes, When, and Why. For hair loss associated with menopause, see Why Women Lose Hair: The 6 Most Common Causes and What Helps.