Hormone Science

In November 2025, the FDA did something it hadn’t done in 23 years: it corrected itself.

The agency removed the black box warnings from all menopausal hormone therapy (MHT) products containing estrogen, specifically the warnings related to cardiovascular disease, breast cancer, and probable dementia. For two decades, those warnings shaped prescribing behavior, shaped what women were told by clinicians, and limited millions of women from access to MHT. Prescriptions had plummeted after 2003, when the warning described increased risks of cardiovascular disease, stroke, breast cancer, and dementia. FDACNN

The removal doesn’t mean hormone therapy is safe for everyone. It means the old framing was too blunt to be useful.

This article is our attempt at a sharper framing: what the evidence actually supports, what it doesn’t, and where the current cultural conversation is departing from evidence. We hope to give you a map to make more informed decisions about hormone therapies.

A brief history on what happened with the WHI.

Almost everything in the MHT conversation traces back to a single trial: the Women’s Health Initiative, whose initial findings were published in JAMA in 2002. It’s worth understanding what that trial studied, because the gap between the study population and the real-world population is significant.

The WHI enrolled postmenopausal women with an average age of 63. The trial used oral conjugated equine estrogen combined with a synthetic progestin called medroxyprogesterone acetate. It found increased risks of breast cancer, cardiovascular events, and stroke. Those findings were based on that specific population, using those specific formulations.

What happened next is a classic example of how science can get transmitted badly. The findings were generalized. Class-wide warnings were applied to all hormone therapies regardless of type, dose, route of administration, or the age of the woman considering them. The “timing” or “window” hypothesis, which suggested women initiating closer to menopause onset have different benefit-risk profiles than those initiating therapy years later, emerged from subsequent analyses but took years to reach clinical practice. Patient Care Online

A 47-year-old perimenopausal woman weighing MHT in 2005 was making that decision based on data from 63-year-old postmenopausal women using oral synthetic hormones. The evidence didn’t fit the question. The label didn’t acknowledge that mismatch. Tens of millions of women made decisions in that gap.

What we know with reasonable confidence today

Some findings in this space are robust enough to state without heavy qualification.

MHT is the most effective treatment available for vasomotor symptoms. Hot flashes, night sweats, the 3am wake-ups that define perimenopause for many women. Few intervention works for these symptoms, bar MHT. Today, MHT’s effectiveness for vasomotor symptoms is clinical consensus across The Menopause Society, ACOG, and every major specialty body. If symptom relief is the goal, the evidence for MHT’s efficacy is stronger than for any alternative intervention.

Bone protection is consistent and well-characterized. Randomized controlled trials and meta-analyses have consistently shown that MHT is efficacious in reducing the risk of fractures, irrespective of age, falls risk, or baseline fracture probability. The mechanism is understood: estrogen maintains the equilibrium between bone resorption and bone formation. MHT decreases the incidence of osteoporosis-related fractures even in postmenopausal women not diagnosed with osteoporosis, with an efficacy similar to that of bisphosphonates. There is one important caveat: when MHT is discontinued, rapid bone loss occurs, mostly within the first two years, identical to that seen within the first two years of menopause. The protection likely is contingent on continued use. nih + 2

Low-dose vaginal estrogen for genitourinary symptoms is safe, effective, and undertreated. Genitourinary syndrome of menopause, which includes vaginal dryness, urinary urgency, and pain during sex, affects the majority of postmenopausal women. The FDA agreed to remove the boxed warning on low-dose vaginal estrogen therapies, noting that the warning may have been a deterrent to use of a therapy that is safe and effective. The systemic absorption from low-dose vaginal estrogen is minimal. This is the most under-treated symptom cluster in the perimenopause space, and the risk profile for local treatment is considered low for most women. The Menopause Society

Timing matters for cardiovascular risk, and this is now mainstream clinical consensus. The “timing hypothesis” proposes that MHT initiated within 10 years of menopause onset or before age 60 may confer cardiovascular benefit, whereas later initiation may increase cardiovascular risk. In women who started hormone therapy earlier, there was a reduced risk of coronary heart disease compared to later initiators, with a risk ratio of 0.66 for estrogen alone (i.e. 34% reduction in risk) and 0.72 for estrogen with progestin (i.e. 28% reduction in risk). The FDA’s updated labeling now explicitly incorporates this timing distinction. The new label adds language recommending that hormone therapy be started in women younger than 60 or within 10 years of starting menopause, and eliminates the recommendation to use MHT at the lowest dose for the shortest amount of time. Frontiers

Route of administration is not a minor detail. Transdermal estradiol, meaning patches, gels, and sprays absorbed through the skin, bypasses first-pass liver metabolism. Oral estrogen doesn’t. That metabolic difference matters: oral estrogen increases clotting factors in the liver in a way transdermal formulations do not. Initiation within 10 years of menopause as well as the use of transdermal estradiol at low to moderate doses are favored when cardiometabolic or thrombotic risk is salient. If your clinician is discussing MHT with you, the conversation about the route is crucial. PubMed Central

What the evidence supports directionally, but incompletely

Several claims are reasonably clear in direction but they’re not settled science. Unfortunately, they’re being communicated in public conversations with more certainty than the evidence warrants. Each one is labeled accordingly.

Cognitive protection and Alzheimer’s risk. Direction: promising, particularly for early initiators. Verdict: not established.

This is the most emotionally resonant claim in the current MHT conversation, and the one most ahead of its evidence base. Women make up two-thirds of Alzheimer’s cases. The biological mechanism for estrogen’s neuroprotective role is plausible and supported by animal models. Several recent observational studies link early MHT initiation to reduced Alzheimer’s risk. But the WHI, in contrast, found increased dementia risk in older initiators using oral combined therapy. The RCT evidence is mixed, and the timing dependency may be especially critical here: what might protect a 50-year-old brain could harm a 70-year-old one. File this under “worth watching closely, not as gospel.”

Mood and perimenopausal depression. Direction: real effect, particularly in early postmenopause. Verdict: population-dependent.

Estrogen supplementation, particularly in early postmenopause, has been associated with modest reductions in depressive symptoms, with transdermal estradiol showing the most consistent benefits. The SWAN study data shows perimenopause doubles depression risk, peaking in late perimenopause. What’s less established is whether MHT is the right treatment for perimenopausal depression as opposed to postmenopausal depression. The perimenopause transition involves fluctuating rather than absent hormones, which is a different physiological context, and the RCT evidence is thinner for this specific population. Whether the depression is primarily estrogen-driven, or has other contributing factors, changes the treatment calculus significantly. PubMed Central

Metabolic health and body composition. Direction: modest positive effect. Verdict: not a primary indication.

Some evidence suggests MHT reduces visceral fat accumulation and improves insulin sensitivity in postmenopausal women. The mechanism is biologically plausible: estrogen influences fat distribution and glucose metabolism. The effect size is modest and highly variable across individuals. This is not a weight management intervention and shouldn’t be positioned as one. The women gaining the most visceral fat during perimenopause despite unchanged diet and exercise aren’t failing at something. They’re experiencing a well-documented metabolic shift. MHT may attenuate it, partially, in some women.

Sleep. Direction: real improvement, mechanism-dependent. Verdict: conditional.

A 2024 Korean study reported significant improvements in sleep quality after one and three months of MHT, and systematic reviews indicate that improvements in sleep frequently accompany reductions in vasomotor symptom burden, particularly nocturnal hot flashes and night sweats. The key word is “accompany.” MHT improves sleep primarily by reducing the vasomotor symptoms that disrupt it. If your sleep disruption is driven by night sweats waking you at 2am, MHT may transform your nights. If your sleep disruption has other primary drivers, such as anxiety, cortisol dysregulation, or sleep apnea, the effect is less predictable. The mechanism matters for the outcome. PubMed Central

Cardiovascular protection as a treatment goal. Direction: possible benefit for early initiators as a side effect. Verdict: not an approved indication.

Current clinical guidelines are explicit on this. Cardiovascular prevention is not an indication for MHT. The timing hypothesis supports a more favorable cardiovascular profile for early initiators, and there are plausible mechanisms for benefit. But “may confer cardiovascular benefit under the right circumstances” is not the same as “start MHT to protect your heart.” These are meaningfully different claims and the evidence supports only the first. PubMed Central

What remains unclear

Breast cancer risk: the number that won’t simplify.

This is the most important, most contested, and most misrepresented finding in the entire MHT landscape. The honest answer is that it depends on formulation, duration, and individual risk profile.

All systemic regimens are accompanied by elevated breast cancer risk, with norethisterone-estradiol associated with the highest risk increases and dydrogesterone-estradiol carrying the lowest risk increase among combination therapies. Estrogen-only therapy, available only to women without a uterus, carries a lower and possibly neutral risk signal for shorter durations. European Journal of Cancer

The absolute numbers are important to hold alongside the relative risk language. For women of average weight in developed countries, five years of MHT starting at age 50 would increase breast cancer incidence at ages 50-69 by about one in every 50 users of estrogen-progestogen therapy. It is not the same as “causes breast cancer” in the way the black box warning implied for all users. Context matters: one in 50 over 19 years means 49 in 50 are unaffected. The Lancet

What the FDA removal represents is a recalibration, not an exoneration. The Menopause Society noted that systemic estrogen still comes with potential risks in certain individuals that should be reviewed in detail with women initiating therapy, and that risks are low for younger, healthy women initiating hormone therapy closer to the menopause transition. The risk didn’t disappear. The framing got more accurate. The Menopause Society

A 2025 NIEHS pooled analysis extended prior findings to younger women, helping guide decision-making for women as they go through menopause. This is active research territory. NIEHS

Micronized progesterone versus synthetic progestins: does it matter?

Observational studies consistently suggest that micronized progesterone, the bioidentical form, carries a lower breast cancer risk signal than synthetic progestins like medroxyprogesterone acetate. The biological mechanism is plausible: synthetic progestins bind to progesterone receptors differently than natural progesterone and may have different effects on breast tissue. Practitioner consensus is moving toward preferring micronized progesterone where combination therapy is indicated. But head-to-head RCT data comparing the two directly is limited. This is a case where practitioner consensus is ahead of definitive trial evidence, which doesn’t make it wrong. It makes it a working hypothesis that reasonable clinicians can act on.

Long-term use beyond five to seven years.

The evidence base is dominated by studies covering shorter durations. The FDA removed the recommendation to use MHT at the lowest dose for the shortest amount of time. That removal reflects the absence of evidence supporting that blanket restriction, not evidence that long-term use is risk-free. These are different things. What happens with 10, 15, or 20 years of use is less characterized than the current public conversation acknowledges. This is not a reason to avoid MHT. It is a reason to have ongoing conversations with your clinician rather than a one-time decision.

MHT in perimenopausal women specifically.

Most of the evidence base studied postmenopausal women with stable, low hormone levels. Perimenopause is a different physiological context: hormones are fluctuating, sometimes wildly, not absent. The benefit-risk calculation in this population may differ from postmenopausal women in ways that the available literature can’t fully characterize. The population most actively seeking MHT guidance right now is also the population with the thinnest direct evidence. This is a research gap. It is a reason to approach the decision with appropriate humility and individualization.

What’s being oversold

By now, you probably have a sense of which claims circulating in the current perimenopause conversations are ahead of evidence and should be scrutinized by you and your clinician.

“MHT is for every symptomatic woman.” It isn’t. Women with hormone-sensitive cancers, active liver disease, unexplained vaginal bleeding, history of blood clots, or certain cardiovascular conditions remain contraindicated. Decisions around MHT must remain individualized, and providers must continue to counsel patients about potential risks. The pendulum swinging from “MHT is dangerous” to “MHT is for everyone” is swinging past the evidence in both directions. Society of Gynecologic Oncology

“Bioidentical hormones are safer.” Compounded bioidentical hormones are not FDA-regulated, which means quality, purity, and dose consistency vary by compounding pharmacy. FDA-approved bioidentical options exist, including micronized progesterone and transdermal estradiol, and are preferable precisely because they’re standardized and their safety profiles are characterized. “Natural” is not a pharmacological safety category.

“MHT protects your brain.” A promising signal, not an established indication. The neuroprotection claim is emotionally resonant and biologically plausible. It is getting ahead of its RCT evidence in the current cultural conversation. Use it as a reason to stay curious about the research. Don’t use it as a primary reason to start therapy.

“Start immediately.” The timing hypothesis supports early initiation relative to menopause onset, not urgency at the first hot flash. The clinical conversation matters: individual risk profile, symptom severity, contraindications, goals. The worst version of the current pendulum swing is women feeling they need to start MHT now, before a proper clinical evaluation, because they’ve been told the window is closing. The window is not a crisis. It’s a consideration.

Questions worth bringing to your clinician

This piece is not a prescription. What we aim to do is to give you a better set of questions for an informed and individualized conversation with your clinicians:

• What type and route of MHT are we considering, and why those specifically for my profile?
• What does that mean for my timing given where I am in my perimenopause/menopause phase?
• What is my personal breast cancer risk, including family history and any genetic factors?
• Which of my specific symptoms does the evidence suggest MHT will likely address, and which might not respond?
• If I’m not a candidate for or not interested in MHT, what does the evidence say about the alternatives for my specific symptom profile?
• How will we monitor and reassess over time, rather than treating this as a set-and-forget decision?

Sources

• Women’s Health Initiative Writing Group. “Risks and Benefits of Estrogen Plus Progestin in Healthy Postmenopausal Women.” JAMA 288, no. 3 (2002): 321-333.
• The Menopause Society. “The 2022 Hormone Therapy Position Statement of The Menopause Society.” Menopause 29, no. 7 (2022): 767-794.
• Collaborative Group on Hormonal Factors in Breast Cancer. “Type and Timing of Menopausal Hormone Therapy and Breast Cancer Risk.” The Lancet 394, no. 10204 (2019): 1159-1168.
• Wang Y, et al. “Update of the Impact of Menopausal Hormone Therapy on Breast Cancer Risk.” European Journal of Cancer (2025). doi:10.1016/j.ejca.2025.115340.
• Cho L, et al. “Rethinking Menopausal Hormone Therapy: For Whom, What, When, and How Long?” Circulation 147, no. 7 (2023): 597-610.
• O’Brien KM, et al. “Hormone Therapy Use and Young-Onset Breast Cancer: A Pooled Analysis of Prospective Cohorts.” NIEHS (2025).
• Morbi A, et al. “The Impact of Hormone Replacement Therapy on Cardiovascular Health in Postmenopausal Women.” Frontiers in Reproductive Health (2026).
• FDA. “FDA Approves Labeling Changes to Menopausal Hormone Therapy Products.” November 2025.

 

Waves Women does not provide medical diagnosis or treatment. Always consult your healthcare provider for personalized medical advice.