Hormone therapy: 10 key questions answered by experts

Despite decades of use and a growing body of evidence in its favor, hormone replacement therapy (HRT) remains surrounded by persistent myths and misunderstandings. Dr. Mark Hyman and Dr. Cynthia Geyer of the UltraWellness Center address the questions they hear most often from patients — including the ones people are afraid to ask their doctors.

1. Is hormone therapy safe?

For most women under 60 who are within 10 years of menopause onset, hormone therapy is safe and effective. The concern about safety originated with the 2002 Women's Health Initiative (WHI) study, which reported a 26% increase in breast cancer risk. However, that study used synthetic conjugated equine estrogens (Premarin) combined with a synthetic progestin (Provera/Prempro), administered to women with an average age of 63 — well past the therapeutic window.

Modern bioidentical hormone therapy, particularly transdermal estradiol combined with micronized progesterone, has a substantially different risk profile than the hormones used in the WHI.

2. Does HRT cause breast cancer?

The WHI finding is the source of most of this fear. The absolute increase in risk was small: roughly 8 additional cases per 10,000 women per year. Context matters — that risk is comparable to drinking one glass of wine per day or having a BMI over 30. The type of hormone used also matters significantly. Synthetic progestin (medroxyprogesterone acetate) is associated with a higher breast cancer risk than bioidentical progesterone.

Women with a BRCA mutation, prior breast cancer diagnosis, or strong family history should have an individualized conversation with an oncologist before starting.

3. What is the timing hypothesis?

The timing hypothesis refers to the observation that the benefits of HRT — particularly cardiovascular and cognitive protection — are largely limited to women who start therapy within 10 years of menopause or before age 60. Starting after that window may confer less benefit and could carry different risks in women who already have atherosclerosis.

This is one of the most important concepts in contemporary menopause medicine and is one reason why early perimenopause is increasingly seen as the ideal time to initiate hormone therapy.

4. What is bioidentical hormone therapy?

Bioidentical hormones are molecules that are structurally identical to the hormones produced by the human body. Estradiol (the primary estrogen), progesterone, and DHEA are all available in bioidentical form. They are derived from plant sources (typically yams or soy) and processed to match the human hormone structure exactly.

The FDA has approved several bioidentical hormone preparations. The important distinction is that FDA-approved bioidentical products have been tested for purity, potency, and safety. Compounded bioidentical formulations prepared by compounding pharmacies are not FDA-approved and may vary significantly in dose and quality.

5. Oral vs. transdermal estrogen — does it matter?

It matters significantly. Oral estrogen is metabolized through the liver on the first pass, which increases coagulation factors and raises the risk of blood clots and stroke — particularly in women with existing cardiovascular risk. Transdermal estrogen (patches, gels, sprays) bypasses this effect entirely.

Current clinical guidance generally favors transdermal delivery for most women. The exception is women with osteoporosis, where oral estrogen may have a stronger effect on bone density markers.

6. Do I need progesterone if I still have my uterus?

Yes. Estrogen stimulates the uterine lining. Without progesterone to oppose that stimulation, the risk of endometrial hyperplasia and endometrial cancer increases significantly. Any woman with an intact uterus who takes systemic estrogen must also take progesterone.

Women who have had a hysterectomy can take estrogen alone, which has a notably different and more favorable risk profile than the estrogen-plus-progestin combination studied in the WHI.

7. What is the difference between progesterone and progestin?

Progesterone refers to bioidentical progesterone — a molecule identical to what the ovaries produce. Progestin is a synthetic compound that mimics some but not all of progesterone's functions and has different receptor activity and a different risk profile. The WHI used medroxyprogesterone acetate (MPA), a synthetic progestin, which is associated with higher breast cancer risk. Bioidentical oral micronized progesterone (Prometrium) appears to have a much lower, possibly neutral, breast cancer risk.

8. What lab tests should I have before starting HRT?

A thorough baseline includes: estradiol, progesterone, FSH, LH, total and free testosterone, DHEA-S, thyroid panel (TSH, free T3, free T4), complete metabolic panel, complete blood count, lipid panel, and fasting insulin. Advanced cardiovascular markers — including apolipoprotein B, Lp(a), and high-sensitivity CRP — provide a clearer picture of cardiovascular risk.

Function Health provides access to over 160 lab markers annually, which covers the full baseline panel needed before and during hormone therapy.

9. Can HRT help with mood, brain fog, and sleep?

Yes. These are among the most common reasons women seek hormone therapy. Estrogen has direct effects on serotonin, dopamine, and acetylcholine systems. The cognitive changes women experience during perimenopause — memory gaps, difficulty concentrating, word retrieval problems — are largely hormone-driven and often meaningfully improve with estrogen therapy.

Progesterone has anxiolytic and sleep-promoting effects. Many women report significant improvement in sleep quality within weeks of starting bioidentical progesterone.

10. Who should not take HRT?

Absolute or strong contraindications include: active or recent estrogen-sensitive breast cancer, unexplained vaginal bleeding, active blood clot or stroke, active liver disease, or known hypersensitivity to hormone preparations. Women with BRCA mutations require individualized risk-benefit discussions with a specialist. Most other factors (family history, benign breast conditions, migraine with aura) are relative contraindications that require careful individualized assessment rather than automatic exclusion.