Definition: The Women's Health Initiative (WHI) is a large set of studies in postmenopausal women aged 50 to 79 that tested daily oral conjugated estrogens, alone or with the progestin medroxyprogesterone acetate (MPA), against placebo. Its findings on stroke, blood clots, breast cancer and dementia appear on US estrogen labels.
| Outcome | Estrogen alone vs placebo | Estrogen plus MPA vs placebo |
|---|---|---|
| Stroke | 45 vs 33 | 33 vs 25 |
| Blood clots (VTE) | 30 vs 22 | 35 vs 17 |
| Pulmonary embolism | Not listed here | 18 vs 8 |
The estrogen-alone arm followed women for 7.1 years. The WHI Memory Study (WHIMS) found a higher risk of probable dementia in women 65 and older. With estrogen plus MPA, invasive breast cancer had a relative risk of 1.24 on the Bijuva and Prometrium labels.
Labels of other estrogen products quote WHI even though it tested only oral conjugated estrogens and MPA. The Bijuva and Prometrium labels say how the findings apply to their products is not known. The Bijuva label says to consider starting it in women under 60 or within 10 years of menopause, and from February 2026 it no longer has a boxed warning, though the WHI risks stay in its warnings.
The WHI numbers are rates per 10,000 women each year, so they read small but add up with time. Your age, the years since menopause and how long you have been on hormones all change the picture. A log with your start date and every product change keeps that history in one place.
Read more on Dose Track: Premarin side effects · Bijuva side effects · Prometrium side effects · Vagifem side effects