Is Hormone Therapy Safe? What 2020s Evidence Actually Says

The timing hypothesis

The single most important concept in modern menopausal hormone therapy is the 'timing hypothesis': the risk-benefit profile is favourable when therapy starts within 10 years of menopause and before age 60, and becomes progressively less favourable when started 15+ years post-menopause.

The much-quoted increase in cardiovascular events from the 2002 WHI trial was largely driven by women who started therapy in their 60s and 70s, not those in the typical 45–55 window.

The breast cancer question, honestly

Estrogen-only therapy (used in women without a uterus) does not appear to increase breast cancer risk in most modern studies, and may slightly reduce it. Combined estrogen + progestogen therapy is associated with a small absolute increase in breast cancer risk after several years of use — smaller than the risk associated with two drinks of alcohol per day, or with being overweight.

This risk is not zero. It should be discussed transparently, weighed against quality-of-life benefits and other health protections (bone, mood, sleep, potentially cardiovascular in the early window), and revisited annually.

Blood clots and why route matters

Oral estrogen slightly increases the risk of venous thromboembolism (blood clots), because it passes through the liver and stimulates clotting factor production. Transdermal estradiol (patch or gel) does not — it bypasses liver first-pass metabolism. For this reason, transdermal is preferred for most patients today, particularly those with any additional clotting risk (overweight, migraine with aura, smoking history).