The WHI, HRT, and What Got Lost in Translation
When I started practicing family medicine, my training in hormone replacement therapy was limited. I'd heard about "bioidentical hormones" but had no formal education on what defined them or why they were growing in popularity — beyond a single lecture from an OB-GYN who discouraged their use.
To understand why, you need to know about the Women's Health Initiative.
What Was Studied
The WHI enrolled roughly 161,000 postmenopausal women aged 50 to 79 — the majority over 60 — in a large, ethnically and geographically diverse trial. The hormone arm studied two synthetic compounds: Conjugated Equine Estrogen (CEE, derived from horse estrogen) and Medroxyprogesterone Acetate (MPA, a synthetic progestin).
What Was Published
In 2002, the combined hormone trial was stopped early when data showed increased risks of invasive breast cancer, heart disease, stroke, and blood clots.
What Was the Impact
Women around the world were taken off hormone replacement therapy almost overnight. Medical schools and residencies stopped teaching HRT. By the time I trained in 2017, the guidance was clear: women should only be on HRT for a maximum of three years, after which it should be stopped unless they accepted an increased risk of breast cancer.
What this meant in practice: about three years of relief from hot flashes, sleep disruption, and mood swings — followed by a forced withdrawal that brought all of it back, plus an elevated risk of heart disease, osteoporosis, and dementia. There was no informed consent process explaining that stopping hormones traded one set of risks for another. And many of those risks — cardiovascular disease, bone loss, cognitive decline — can be meaningfully reduced by bioidentical estrogen.
What Was Overlooked
Here's what the original WHI coverage largely missed — and what the medical community is only now beginning to correct:
The study never distinguished between bioidentical and synthetic hormones. CEE and MPA are not chemically identical to the hormones the human body produces. Bioidentical hormones — which can be manufactured in a lab — are structurally identical to endogenous estrogen and progesterone. That distinction matters enormously.
Synthetic CEE and oral bioidentical estradiol are both metabolized by the liver, where clotting factors are produced — which is why they're associated with blood clots. Transdermal bioidentical estradiol bypasses the liver entirely and does not carry the same clotting risk.
The breast cancer association appears linked specifically to MPA and synthetic progestins, which are roughly 50 times more potent than bioidentical oral micronized progesterone. Studies currently underway are evaluating whether bioidentical progesterone carries meaningfully lower breast cancer risk — and early data suggests it does.
What We Know Now
Progesterone converts to allopregnanolone — a naturally occurring anti-anxiety molecule that supports sleep and mood regulation. This means that even women who have had their uterus and ovaries removed, who were historically told to take estrogen alone, may benefit from progesterone replacement as well.
Despite this evolving evidence, a 2026 Mayo Clinic study using insurance claims data from 2007 to 2023 found that systemic menopausal hormone therapy use among US women aged 40 and older dropped from 4.4% in 2007 to 1.7% in 2023. The real number may be higher — compounded prescriptions aren't captured in claims data — but the gap between who might benefit and who is actually being treated remains significant.
One patient at a time, every primary care physician needs to evaluate and individualize an approach to hormone therapy for every peri- and postmenopausal woman in their practice.
For Colorado patients open to Direct Primary Care, book a call with me and let's figure out what yours might look like.
📞 Call or text: 720-856-4058 🔗 Book a free 10-min call: www.metronomemd.com/book
