A Peer-Reviewed Journal JustCalled for MPA to BeRemoved from the Market

For decades, medroxyprogesterone acetate MPA has been the default progestin in hormone replacement therapy prescriptions across the United States. A December 2025 publication in Frontiers in Global Women's Health is now calling for that to end entirely.

This isn't a fringe blog post or a social media opinion. It's a peer- reviewed, indexed journal making a categorical recommendation: eliminate the sale of MPA-containing products due to elevated risks of heart attack and breast cancer. And when you look at the science behind that recommendation, it's hard to argue.

B E F O R E T H E D ATA

MPA Is Not Progesterone

This is perhaps the most important thing to understand before anything else. MPA is a synthetic progestin derived from testosterone. It does not bind the progesterone receptor cleanly the way natural progesterone does. Instead, it binds to three other receptor families with significant downstream effects:

ANDROGEN RECEPTOR

GLUCOCORTICOID RECEPTOR

MINERALOCORTICOID RECEPTOR

PROGESTERONE RECEPTOR (WEAK)

This off-target binding is not a minor pharmacological footnote. It shapes virtually every adverse outcome we see in the data.

"MPA binds three receptor systems it was never meant to activate and women have been paying the price for that for over twenty years."

T H E S T U D Y T H AT C H A N G E D E V E R Y T H I N G

The WHI Used CEE + MPA And That Combination Is the Problem

The Women's Health Initiative (WHI) study produced the breast cancer and cardiovascular risk signals that scared a generation of women away from hormone therapy entirely. The HRT crisis that followed millions of women going untreated through menopause was one of the most consequential medical overcorrections in modern history.

What most people don't know: the WHI used conjugated equine estrogen (CEE) combined with MPA. That specific pairing carries the highest venous thromboembolism (VTE) risk of any HRT formulation documented in the literature. The problem was never hormone therapy. It was the formulation choice and we spent two decades paying for it.

4 3 , 0 0 0 W O M E N · L A R G E U K P O P U L AT I O N S T U D Y

The Breast Cancer Numbers Are Stark

M I C R O N I Z E D P4

0.99

Neutral to breast tissue essentially no increased risk

SY N T H E T I C P R O G E ST I N S ( MPA)      

1.28       

Amplifies proliferative effects in breast tissue

Breast cancer odds ratio. Source: Large UK population cohort study, n=43,000 women.

An odds ratio of 0.99 means micronized progesterone is essentially neutral to breast tissue indistinguishable from baseline risk. An odds ratio of 1.28 for synthetic progestins represents a meaningful, clinically significant elevation. That is not a rounding error. That is a different drug with a different risk profile.

W H AT Y O U R PAT I E N T N E V E R G E T S O N MPA

MPA Cannot Convert to Allopregnanolone

Micronized progesterone converts to allopregnanolone. MPA does not.

That conversion is the mechanism behind some of progesterone's most clinically meaningful benefits — the ones your patients on MPA are quietly missing

Allopregnanolone is a neuroactive metabolite that binds GABA-A receptors in the brain —the same receptors targeted by benzodiazepines. When micronized progesterone is metabolized properly, patients often experience:

→ Measurable sleep improvement within the first treatment cycle

→ Reduced anxiety and improved mood stabilization

→ Neurological calm through GABA-A receptor engagement

MPA delivers none of this. Instead, it delivers off-target receptor activity androgenic, glucocorticoid, and mineralocorticoid effects that can actively counteract the benefits of estrogen therapy.

So Here Is the Real Question

When a bioidentical option exists with a lower breast cancer signal, lower clotting risk, and documented neurological benefit...

What is the clinical rationale for choosing MPA?

There isn't one.

What This Means in Practice

The data has been pointing in this direction for years. What changed in December 2025 is that researchers publishing in a peer-reviewed, indexed journal said it plainly not as a recommendation to "consider alternatives," but as a direct call to eliminate MPA from

the market entirely due to heart attack and breast cancer risk. For clinicians still reaching for MPA by habit, this is the paper to read. For women currently on MPA-containing HRT, this is a conversation worth having with your provider about whether micronized progesterone (oral or topical) might be a more appropriate option for your situation.

The formulation matters. It has always mattered. The science has simply gotten louder.

SOURCE: FRONTIERS IN GLOBAL WOMEN'S HEALTH, DECEMBER 2025. PEER-

REVIEWED. INDEXED. · DATA REFERENCED FROM LARGE UK POPULATION COHORT

STUDY (N=43,000). · REFERENCED VIA @HRTUNIVERSITY.

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