Estrogen Replacement Therapy

Estrogen is not a single hormone but a family of three. Estradiol (E2) is the most potent and the dominant form during a woman's reproductive years, produced mainly by the ovaries. Estrone (E1) is weaker and becomes the predominant circulating estrogen after menopause, made largely in fat tissue rather than the ovaries. Estriol (E3) is the weakest of the three and rises dramatically during pregnancy. When physicians talk about restoring estrogen in menopause, they are usually talking about restoring estradiol — the form the body relied on for decades.

Estrogen receptors are found throughout the body, not merely in the reproductive organs, which is why estrogen loss produces such a wide and often surprising range of symptoms. Estrogen helps maintain bone density by restraining the cells that break down bone. It supports the flexibility and lining of blood vessels. It influences serotonin and other neurotransmitters involved in mood, memory, and sleep architecture. It maintains collagen in skin, and it keeps the tissue of the vagina, urethra, and bladder thick, elastic, and well lubricated. Estrogen also participates in how the body regulates temperature, which is why its loss so often announces itself as hot flashes.

In the United States, natural menopause occurs on average around age 51, but the decline begins years earlier. During perimenopause, estradiol does not fall smoothly — it fluctuates, sometimes swinging higher than normal before dropping, which is why this stage can feel so erratic. Once the ovaries stop producing estradiol in meaningful amounts, the deficiency becomes permanent unless it is treated. Understanding which symptoms trace back to estrogen specifically, rather than to progesterone, thyroid, or testosterone, is the diagnostic work that shapes effective treatment.

The most recognizable symptoms of low estrogen are vasomotor: hot flashes and night sweats. These are sudden, uncomfortable surges of heat driven by a narrowing of the brain's thermoregulatory comfort zone when estrogen withdraws. For many women they are merely irritating; for others they arrive dozens of times a day, ruin sleep for years, and quietly erode work performance and quality of life. Hormone therapy remains the single most effective treatment available for them.

A second cluster of symptoms — collectively called the genitourinary syndrome of menopause — is far less often discussed but affects a large share of women and, unlike hot flashes, tends to worsen with time rather than fade. Falling estrogen thins and dries the tissue of the vagina, vulva, urethra, and bladder. The result can include vaginal dryness, burning or irritation, pain with intercourse, urinary urgency and frequency, and recurrent urinary tract infections. Many women assume these changes are simply part of getting older and never raise them with a physician. They are treatable.

Estrogen loss also reaches the brain and the skeleton. Women commonly report disrupted sleep, difficulty concentrating, word-finding problems, memory lapses, low mood, and a shorter fuse for stress. Bone loss accelerates sharply in the years immediately surrounding menopause, which is why estrogen deficiency is a principal driver of postmenopausal osteoporosis — a process that produces no symptoms at all until a fracture occurs. Joint aches, thinning skin, hair changes, and shifts in body composition round out a picture that many women recognize immediately once it is described to them.

No area of women's medicine has been shaped more by a single study than estrogen therapy. When the Women's Health Initiative published its first results in 2002, headlines announced that hormone therapy caused breast cancer and heart disease, prescriptions collapsed worldwide, and an entire generation of women was advised to stop or never start. Two decades of reanalysis have substantially revised that picture, but the original headlines have proved far more durable than the corrections.

Two facts are worth knowing. First, the WHI had two separate arms, and they produced different results. The arm that combined estrogen with a synthetic progestin showed the increase in breast cancer risk that drove the headlines. The estrogen-alone arm — women who had undergone hysterectomy and took conjugated equine estrogen without a progestin — did not. In extended follow-up of that trial published in JAMA in 2020, prior use of estrogen alone was associated with a statistically significant reduction in both breast cancer incidence and breast cancer mortality. Second, the average participant in the WHI was well past menopause at enrollment, in her sixties, which is not the population that typically seeks treatment for menopausal symptoms.

That second point became the basis of what is now called the timing hypothesis, and it is reflected in current guidance. The 2022 Hormone Therapy Position Statement of The Menopause Society (formerly the North American Menopause Society) concludes that for women younger than 60 or within 10 years of the onset of menopause who have no contraindications, the benefit-risk ratio is favorable for treating bothersome vasomotor symptoms and for preventing bone loss. For women starting therapy more than 10 years out from menopause or after age 60, the same statement finds the balance less favorable because the absolute risks of coronary heart disease, stroke, blood clots, and dementia are higher in that group. The statement is equally clear that risk depends on the type of hormone, the dose, the route of administration, the duration of use, the timing of initiation, and whether a progestogen is used — which is precisely why this therapy calls for a specialist rather than a standard prescription.

Bioidentical estradiol is molecularly identical to the estradiol your ovaries produced. It is manufactured from plant sources and processed so that the finished molecule matches human estradiol exactly, which means your receptors recognize and use it the way they used your own hormone. This is the form Dr. Riegel prescribes.

Not every estrogen prescription is estradiol. Conjugated equine estrogens — the preparation studied in the WHI — are a mixture of estrogen compounds derived from the urine of pregnant mares, several of which do not occur in the human body at all. Synthetic estrogens differ in structure as well. These preparations have decades of clinical use behind them and are not without merit, but they are not the same molecule your body made, and there is no clinical reason to accept a different molecule when an identical one is available.

Dr. Riegel's work in this area is the foundation of the practice. Four years of hormone research at UT Southwestern Medical School and more than three decades of clinical hormone medicine produced roughly forty proprietary bioidentical formulations, refined patient by patient over more than twenty years. Those formulas exist because commercially available fixed-dose products could not deliver the precision his patients needed — the right estrogen, at the right dose, in the right ratio to the other hormones, adjusted as the body responds.

How estrogen enters the body changes what it does once it is there, and this is one of the most consequential and least understood decisions in hormone therapy. Estrogen taken orally is absorbed through the gut and passes through the liver before reaching the general circulation. That first pass through the liver alters the production of clotting factors and other proteins, and it is the mechanism behind the increase in venous thromboembolism risk seen with oral estrogen. Estrogen delivered through the skin bypasses the liver entirely. Observational evidence cited in current menopause guidance suggests transdermal estradiol carries a lower risk of blood clots than oral preparations, which is why route is a genuine safety decision rather than a matter of preference.

Beyond transdermal, Dr. Riegel uses sublingual and other adjustable delivery methods depending on each patient's needs, absorption, and symptom pattern. What these routes share is that the dose can be changed. That matters, because optimizing hormones is iterative — you test, you observe how a patient actually feels, and you adjust. Implanted pellets sit at the other end of that spectrum: once inserted, the dose cannot be reduced or removed for months, which is the central trade-off discussed on our hormone pellet therapy page.

Systemic estrogen is not always the answer. For women whose only complaint is genitourinary — vaginal dryness, painful intercourse, urinary urgency, recurrent infections — low-dose vaginal estrogen treats the tissue directly with minimal absorption into the bloodstream, and it is frequently the right choice for women who cannot or prefer not to take systemic hormones. Some women use both. Matching the delivery method to the problem being solved is a large part of what distinguishes carefully designed therapy from a default prescription.

Estrogen stimulates the endometrium — the lining of the uterus — to grow. In a normal menstrual cycle, progesterone produced after ovulation matures and stabilizes that lining, and the cycle resets. Take estrogen without that counterbalance, and the lining can build up excessively, a condition called endometrial hyperplasia that raises the risk of endometrial cancer over time.

For that reason, established guidance from The Menopause Society and the American College of Obstetricians and Gynecologists holds that any woman with an intact uterus who takes systemic estrogen must also receive adequate progesterone or another progestogen. This is not an optional refinement — it is a core safety requirement of well-designed therapy. Women who have had a hysterectomy generally do not need a progestogen for endometrial protection, which is exactly why the WHI studied them as a separate arm.

Dr. Riegel builds this protection into every estrogen protocol for women with a uterus, using bioidentical progesterone rather than synthetic progestins. In practice the two hormones are rarely considered separately: the ratio between estrogen and progesterone often explains a patient's symptoms better than either number alone, and both are evaluated alongside testosterone and thyroid function. Our progesterone therapy page covers that side of the balance in detail.

Care begins with a thorough evaluation rather than a prescription. Dr. Riegel takes a detailed symptom and medical history, then orders comprehensive laboratory testing that measures estradiol in the context of everything it interacts with — progesterone, total and free testosterone, FSH, DHEA-S, cortisol, and a complete thyroid panel. Estrogen deficiency is frequently accompanied by other hormonal shortfalls, and treating one while ignoring the others produces partial results at best. This is also the stage where candidacy is determined: a personal history of breast cancer, estrogen-sensitive cancer, unexplained vaginal bleeding, active liver disease, or prior blood clots or stroke all change the calculus, and some women are not appropriate candidates for systemic estrogen.

From there, Dr. Riegel designs an individualized protocol — which estrogen, at what dose, by which route, balanced with what progesterone — chosen for your symptoms, your risk profile, and how far you are from menopause. The guiding principle is physiologic replacement: restoring levels to a healthy range rather than pushing them to extremes, using the molecules your body already recognizes. Where a proprietary formulation serves a patient better than a commercially available fixed dose, he uses one.

Follow-up is where hormone therapy is actually made to work. Symptoms and laboratory values are reassessed, doses are titrated, and the balance between hormones is adjusted as your body responds and as your needs change over the years. Age-appropriate screening — including mammography and, when relevant, bone density testing — continues throughout, and the decision to continue therapy is revisited periodically rather than assumed. For patients outside the Dallas–Fort Worth area, this care is available nationwide through The Riegel Center's telehealth program, with laboratory work coordinated locally.