Defining the Terms
The language around hormone therapy is frequently confusing, and the confusion is not always accidental, it is sometimes actively exploited by commercial interests. Understanding the actual distinction requires separating chemical structure from regulatory status, which are two entirely different things.
HRT (hormone replacement therapy) is an umbrella term for any pharmaceutical treatment that replaces hormones that the body is no longer producing in sufficient quantities. It encompasses a wide range of products including estrogen-only preparations, combined estrogen and progestogen preparations, and in some clinical contexts testosterone. HRT includes both FDA-approved pharmaceutical products and, in some definitions, compounded formulations.
Bioidentical hormones refers specifically to hormones that are chemically identical in molecular structure to the hormones naturally produced by the human body. The key bioidentical hormones used in menopause management are 17-beta estradiol (identical to human estradiol), estriol, progesterone (identical to human progesterone), and testosterone. Bioidentical does not describe a product category, it describes a molecular property.
The critical distinction that most marketing obscures: many FDA-approved, mainstream HRT products are bioidentical. Estradiol patches, gels, sprays, and some oral preparations contain 17-beta estradiol, chemically identical to human estradiol. Oral micronized progesterone (brand name Prometrium in the US) contains bioidentical progesterone, not synthetic progestins.
FDA-Approved Bioidentical Hormones
Contrary to how they are often marketed, bioidentical hormones are not an alternative to mainstream medicine, they are part of it. The following widely prescribed, FDA-approved HRT products are bioidentical:
- Estradiol: Available as transdermal patches (e.g., Vivelle-Dot, Climara), gels (EstroGel, Divigel), sprays (Evamist), vaginal rings (Estring, Femring), and some oral forms. All contain 17-beta estradiol, bioidentical to human estradiol.
- Oral micronized progesterone (Prometrium): Bioidentical progesterone, distinct from synthetic progestins such as medroxyprogesterone acetate (MPA) which were used in the Women’s Health Initiative (WHI) trial.
The distinction between bioidentical progesterone and synthetic progestins is clinically significant. The WHI trial’s headline risk findings regarding breast cancer were associated with combined equine estrogen plus medroxyprogesterone acetate, a synthetic progestin. More recent European observational data and some randomised controlled trial data suggest that bioidentical progesterone (micronized) may carry a lower breast cancer risk signal than synthetic progestins, though the debate continues in the literature and clinical practice varies.
Compounded Bioidentical Hormones
Where the landscape becomes more complex, and where legitimate safety concerns exist, is in the realm of custom-compounded bioidentical hormone preparations. These are formulations prepared by compounding pharmacies, typically to a prescribing clinician’s specification, and may include combinations, doses, and delivery routes not available in FDA-approved products.
Custom-compounded formulations are not FDA-approved because they have not undergone the standardised testing required for approval: they have not been evaluated in large randomised controlled trials, their manufacturing processes are not subject to the same quality controls as pharmaceutical manufacturing, and their potency, purity, and absorption characteristics can vary between batches and between pharmacies.
The FDA and major professional bodies including the American College of Obstetricians and Gynecologists (ACOG), and the Menopause Society (formerly NAMS) have published explicit cautions about custom-compounded bioidentical hormones. Concerns include inaccurate dosing, underdosing or overdosing of hormones (which carries real clinical risk), inadequate sterility, and a lack of efficacy evidence for many claimed applications.
Marketing Claims vs Reality
Compounded bioidentical hormones are sometimes marketed using claims that have no basis in scientific evidence, or that misrepresent the evidence that exists. Common misleading claims include: that compounded bioidenticals are “natural” and therefore safer than pharmaceutical products; that they are customised to your “unique hormonal needs” based on salivary hormone testing (which is not a validated clinical tool); that they do not carry breast cancer risk (this has not been established); and that they are superior to FDA-approved bioidentical preparations.
None of these claims are supported by the current evidence base. A bioidentical estradiol molecule is the same whether it comes from an FDA-approved patch or a compounding pharmacy, the relevant differences lie in quality assurance, dosing accuracy, and regulatory oversight.
For most women, FDA-approved bioidentical hormone preparations offer the appropriate combination of molecular structure, safety evidence, and manufacturing reliability. Custom compounding may be appropriate in specific, limited clinical situations, such as when a patient cannot tolerate a standard excipient or requires a dose not commercially available, but this should be under the supervision of a clinician experienced in menopause medicine.
This information is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before making any changes to your health management.