Natural HRT vs Synthetic HRT: What Body-Identical Actually Means and Which Is Right for You

The Language Around HRT Is Confusing on Purpose

Walk into any conversation about hormone replacement therapy and you will quickly encounter terms like natural, synthetic, body-identical, and bioidentical, often used in ways that are inconsistent, misleading, or designed to sell a product. This matters because the terminology shapes how women make decisions about their care.

Understanding what these terms actually mean, how the products differ in practice, and what the research supports can help you cut through the noise and have a more productive conversation with your healthcare provider.

What 'Body-Identical' Really Means

Body-identical hormones are those with a molecular structure that is identical to the hormones produced by the human body. The two most clinically relevant examples are 17-beta estradiol (the main estrogen produced in the body) and micronized progesterone (progesterone in a form that closely mirrors the body's own progesterone).

Body-identical hormones are not the same as bioidentical hormones as marketed by compounding pharmacies. Regulated body-identical hormones are pharmaceutical-grade products with standardized doses, quality control, and safety data. Many are available by prescription through mainstream healthcare systems in the UK, US, and elsewhere.

The word natural is often used loosely to describe body-identical hormones, which can be derived from plant sources like soy or yams. But this label is less useful than it sounds: the source material is chemically modified in a lab to produce the final product. What matters clinically is the molecular structure, not the origin of the raw ingredient.

What 'Synthetic' Hormones Are

Synthetic hormones have a different molecular structure from those the body produces naturally. The most commonly discussed synthetic hormones in HRT are conjugated equine estrogens (CEE), derived from horse urine and used in older formulations like Premarin, and progestogens such as medroxyprogesterone acetate (MPA), used in older combination HRT products.

These synthetic formulations were the primary form of HRT studied in the large Women's Health Initiative trials in the early 2000s, which raised concerns about breast cancer and cardiovascular risk. The findings from those trials were widely interpreted as applying to all HRT, but researchers and clinicians have since argued that the specific formulations studied, particularly oral CEE plus MPA, may not represent the risk profile of newer body-identical formulations.

The picture is more nuanced now than it was 20 years ago, and the type of hormone, the route of administration, and the timing of starting treatment all appear to matter.

Does the Formulation Affect Risk and Benefits?

Emerging evidence suggests that body-identical estradiol and micronized progesterone may have a more favorable safety profile in certain areas compared to older synthetic formulations, but this does not mean they are without any considerations.

Transdermal estradiol, delivered through patches, gels, or sprays, bypasses the liver's first-pass metabolism in a way that oral estrogen does not. This appears to be associated with a lower risk of blood clots compared to oral estrogen. Micronized progesterone appears to have a more favorable effect on mood, sleep, and possibly breast tissue compared to synthetic progestogens like MPA, though long-term evidence is still accumulating.

For estrogen alone (used by women who have had a hysterectomy), the evidence that it slightly increases breast cancer risk is less strong than for combined HRT. For combined HRT, the type of progestogen appears to matter. Current evidence, while not yet conclusive, suggests micronized progesterone may carry a lower breast cancer risk increment than synthetic progestogens, though this remains an area of active research.

None of this means body-identical HRT is universally safe for everyone. Individual risk factors, health history, and symptom severity all feed into the decision.

Compounded Bioidentical HRT: A Separate Category

Custom-compounded bioidentical hormone preparations, often marketed through private clinics and tested via saliva or blood spot tests, sit in a different category from regulated body-identical medications. These preparations are not subject to the same quality control, standardized dosing, or regulatory oversight as pharmaceutical HRT products.

Major menopause societies, including the British Menopause Society and The Menopause Society in the US, have raised concerns about compounded bioidentical HRT. The concerns include inconsistent hormone doses, unvalidated testing methods, unregulated marketing claims, and a lack of safety data comparable to what exists for regulated products.

If you are interested in body-identical hormones, it is worth knowing that regulated, pharmaceutical-grade body-identical options (such as estradiol patches, gels, and micronized progesterone capsules) are widely available through mainstream prescribers. You do not need to use a compounding pharmacy to access body-identical hormones.

Who Each Option May Suit

Body-identical regulated HRT is now the approach most contemporary menopause specialists favor as a first-line option when HRT is appropriate. Transdermal estradiol plus micronized progesterone is the formulation most supported by current evidence for a favorable balance of benefit and risk in most women.

Older synthetic formulations may still be appropriate in certain contexts, particularly if they have worked well for a specific person and there is no compelling reason to change. Some synthetic formulations are also more accessible or affordable in certain healthcare systems.

Compounded bioidentical preparations may appeal to women looking for very individualized dosing, but the lack of regulatory oversight means they come with greater uncertainty. If you choose this route, it is worth doing so with full awareness of what is and is not known about their safety.

How to Have This Conversation with Your Doctor