The Full Circle of Hormone Replacement Therapy

I distinctly recall my mother being placed on hormone replacement therapy (HRT) after her total abdominal hysterectomy. Years later, alarming data from studies led to the widespread belief that HRT was dangerous—and she was taken off the therapy. In medical school, we were taught that “messing around with these hormones” was risky. However, with re-analyses of those studies and newer research, HRT is now being reconsidered as a viable treatment option. This post reviews how our understanding of HRT has evolved, the benefits it may offer today, and why its use must be tailored to each individual under proper medical supervision.

When HRT Became Bad

Studies in the 1990s raised concerns about HRT, noting that postmenopausal hormone use was associated with a higher incidence of blood clots.¹ The Women’s Health Initiative (WHI) study, which began in 1991, was designed to provide more definitive answers. In 2002, the final results concluded that treatment with HRT in healthy postmenopausal women was linked to increased risks of cardiovascular disease, stroke, blood clots, and breast cancer.² These findings created a climate of caution and led many to believe that HRT was uniformly dangerous, delivering a “final nail in the coffin” for the widespread use of HRT as it was practiced at the time—prompting both the public and clinicians to reconsider its safety.

A Second Look

Critics later questioned whether the WHI study’s methods and participant characteristics were appropriate for all women. Upon reexamining the data, several factors help explain why the initial WHI results painted such a grim picture for HRT. First, the WHI study enrolled women with a mean age well into their 60s—often more than a decade past menopause—when cardiovascular risks naturally increase. This older population may not reflect the outcomes seen in younger, newly menopausal women, who generally have a healthier heart.²

Furthermore, the increased risk of breast cancer reported in the WHI was largely confined to a small subset of women receiving the combined estrogen–progestin regimen. In contrast, women who had undergone a hysterectomy and received estrogen-only therapy did not exhibit a similar increase in breast cancer risk. This distinction suggests that the adverse breast cancer findings may not apply to all hormone therapy users.^2,3

Additionally, the risk of blood clots appears to be influenced by the route of administration. A study published in BMJ in 2008 reported that certain oral formulations of HRT are associated with a higher risk of blood clots compared with transdermal options.⁴

This updated information has led experts to conclude that the balance of benefits and risks may be far more favorable than the original WHI results indicated.

Better Data

More recent studies have provided compelling evidence that modern HRT can offer significant health benefits when used appropriately—especially when initiated near the onset of menopause.

Several randomized trials support cardiovascular benefits with early HRT initiation. For example, starting estrogen therapy soon after menopause may slow the progression of atherosclerosis and improve markers of cardiovascular health.⁵ These data support the “timing hypothesis,” indicating that HRT can be cardioprotective for younger, recently menopausal women.⁶

In addition to cardiovascular benefits, HRT has been shown to reduce the risk of osteoporosis and associated fractures. Even though the Women’s Health Initiative produced some controversial findings, it demonstrated that HRT increased bone mineral density and reduced the risk of hip and other osteoporotic fractures.² This benefit is critical, given the high burden of osteoporosis and fracture-related complications in postmenopausal populations.

Better data from more recent studies show that when HRT is initiated at the right time and tailored to individual risk profiles, it can provide heart protection and improve bone health—underscoring its renewed role in managing menopausal symptoms and long-term health.

It’s Not All Free And Clear

Despite the promising benefits of HRT, it is not without risk. For example, several studies have demonstrated that certain oral estrogen formulations are associated with an increased risk of blood clots.⁴

Cancer risk can be a significant issue in a small subgroup of women. Certain women on combination therapy had a higher risk of breast cancer than those receiving estrogen-only therapy following a hysterectomy.² And while estrogen-only therapy decreases the risk of breast cancer in women without a uterus, it increases the risk of endometrial cancer in women with an intact uterus.⁷

These examples underscore that while HRT can offer substantial benefits, such as improved cardiovascular health, bone density, and symptom relief, it is not universally safe for every woman. The risks vary based on the type of hormone used, the route of administration, patient age, lifestyle factors, and individual health profiles. This variability is why HRT must be carefully tailored and supervised by a knowledgeable healthcare professional.

Symptoms Versus Labs

When it comes to HRT, treatment decisions should be guided primarily by symptoms rather than by laboratory hormone levels. Laboratory values for estrogen and progesterone are typically based on population averages that reflect a wide range of normal variations. For example, in reproductive-age women, estradiol levels can vary dramatically over the menstrual cycle—from as low as about 30 pg/mL to peaks of 200–400 pg/mL at mid-cycle. Similarly, progesterone levels can range from less than 1 ng/mL to 5–20 ng/mL.⁸ These averages, however, may not capture an individual’s unique hormonal baseline. Additionally, the timing of blood draws is critical—ideally, samples should be obtained at the same point in the cycle for meaningful comparisons. Inconsistencies in timing can lead to misinterpretation of a woman’s hormonal status.

The situation is further complicated for women who no longer have regular menstrual cycles or who have transitioned into menopause, where hormone levels can be markedly lower and more variable. Without having baseline hormone levels from earlier in life, it is challenging to determine what a current value truly indicates for a given woman.

For these reasons, clinical guidelines increasingly emphasize that HRT dosing should be based on the patient’s symptoms—such as hot flashes, night sweats, mood changes, and vaginal dryness—rather than relying solely on lab values. This patient-centered approach ensures that therapy is tailored to the individual’s experience, rather than a one-size-fits-all numerical target.

So What Now?

For many women suffering from moderate to severe menopausal symptoms, HRT remains the most effective treatment—when it is prescribed and closely monitored by a physician who specializes in women’s health. It is crucial to avoid unsupervised or unregulated hormone treatments, such as those acquired through online subscriptions or med spas.

Anyone who prescribes these medications must also be available to address questions and potential complications. Case reports and FDA communications have highlighted the risks associated with unregulated compounded bioidentical hormone therapies, including inconsistent dosing that can lead to other health problems. These adverse outcomes emphasize the importance of obtaining HRT under strict medical supervision to ensure both safety and efficacy.

If you are considering HRT, consult with a physician who can carefully assess your individual health history and symptoms. Personalized treatment plans not only optimize the benefits of HRT but also help minimize the potential risks associated with unsupervised hormone use. And while I am a doctor, I am not your doctor. This post is for informational purposes only and does not constitute medical advice. Always consult your physician before starting any therapy.

References

1. Daly E, Vessey MP, Hawkins MM, Carson JL, Gough P, Marsh S. Risk of venous thromboembolism in users of hormone replacement therapy. The Lancet. 1996;348(9033):977-980.
2. Rossouw JE, Anderson GL, Prentice RL, et al. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results From the Women’s Health Initiative randomized controlled trial. Jama. 2002;288(3):321-333.
3. Manson JE, Aragaki AK, Rossouw JE, et al. Menopausal hormone therapy and long-term all-cause and cause-specific mortality: the Women’s Health Initiative randomized trials. Jama. 2017;318(10):927-938.
4. Canonico M, Plu-Bureau G, Lowe GD, Scarabin P-Y. Hormone replacement therapy and risk of venous thromboembolism in postmenopausal women: systematic review and meta-analysis. Bmj. 2008;336(7655):1227-1231.
5. Hodis HN, Mack WJ, Henderson VW, et al. Vascular effects of early versus late postmenopausal treatment with estradiol. New England Journal of Medicine. 2016;374(13):1221-1231.
6. Rossouw JE, Prentice RL, Manson JE, et al. Postmenopausal hormone therapy and risk of cardiovascular disease by age and years since menopause. Jama. 2007;297(13):1465-1477.
7. Gynecologists. ACoOa. Hormone Therapy for Menopause. Updated February 2024. Accessed February 18, 2025. https://www.acog.org/womens-health/faqs/hormone-therapy-for-menopause
8. Faubion SS, Crandall CJ, Davis L, et al. The 2022 hormone therapy position statement of the North American Menopause Society. Menopause. 2022;29(7):767-794.