You have probably heard at least three of these words used in the same conversation about MHT.

Body-identical. Bioidentical. Synthetic. Compounded.

If you assumed they meant similar things, you are not alone, and you are not wrong to be confused. Marketing, the wellness industry and social media have spent two decades using these terms loosely, often interchangeably, sometimes deliberately ambiguously.

They are not the same thing.

The most important word in this conversation is body-identical. When current Australian guidelines talk about modern first-line MHT, they mean body-identical oestrogen and body-identical progesterone. Most of this blog aims to explain the other terms, and where they fit alongside body-identical.

This matters because the words used in marketing and on social media, may not always line up with what your GP says. Knowing which word is which changes what you are actually being asked to choose between.

Some of where this confusion comes from is straightforward.

Some of it traces back to the WHI study. The oestrogen and progesterone used there are different to those most often prescribed today, so Australian practice has moved on. In moving on, women have ended up confused about which products are the older synthetic ones, which are the newer body-identical ones your GP is recommending, and which are the compounded preparations the wellness industry is selling.

Some of it is marketing. Compounded preparations are often described as natural, which makes TGA-approved options sound, by implication, less natural. The reality is the opposite, and we will come to that.

And some of it is geography. Like MHT and HRT in Blog 1, the words body-identical and bioidentical mean slightly different things in Australia, the UK and the US. An Australian woman reading a US Instagram post can easily come away more confused than when she started.

What does "body-identical" mean?

Body-identical hormones have the same chemical structure as the hormones the body produces. Body-identical MHT uses oestradiol (the body's main oestrogen during the reproductive years) and micronised progesterone (the same molecule the body produces).

In Australia, body-identical hormones are available as TGA-approved pharmaceutical preparations. TGA-approved means the Therapeutic Goods Administration has assessed the product for safety, quality and efficacy. The manufacturing is regulated, and that regulation matters in two ways. Every batch is consistent, and the dose in the bottle matches the dose on the label.

The body-identical options available in Australia include:

- Oestradiol. Patches (Estradot), gels (Estrogel, Sandrena), and a spray (Lenzetto).

- Micronised progesterone. Oral capsules (Prometrium).

- Vaginal oestradiol. Pessaries (Vagifem) and cream (Ovestin, available as both cream and pessary).

- Testosterone for women. AndroFeme cream.

These are body-identical, regulated, prescription medications. They are the modern Australian first-line for most women starting MHT.

A practical point worth knowing. Most of the body-identical hormones now prescribed in Australia and internationally are derived from plant sources, often the wild yam, and synthesised in a pharmaceutical laboratory to produce molecules that are exactly the same as the ones the body makes [1,2]. The plant origin is the same for many TGA-approved products and for many compounded products. What differs between them is the manufacturing process and regulation, not the starting material.

What does "natural" mean here, and why is the word being used against women?

This is one of the words the wellness industry leans on the hardest, and it is the one that confuses women most.

Compounded preparations are often described as more natural than TGA-approved options. The implication is that the regulated pharmaceutical product is somehow less natural, and therefore less safe, less close to what the body makes, less worthy of trust.

That is not how the chemistry works.

Both compounded and TGA-approved body-identical preparations are derived from plant sources, often the wild yam, and synthesised in a laboratory [1,2]. The molecule that ends up in the cream, the patch, the gel or the capsule is the same in both cases. Body-identical means body-identical. What differs is regulation, dose consistency, and whether the formulation has been studied for safety and outcomes.

The North American Menopause Society has been blunt about this. The term bioidentical hormones, in their words, is a term invented by marketers and has no clear scientific meaning [3]. The same applies to natural in the way it is used in menopause marketing.

US urologist and women's health advocate Dr Kelly Casperson named this directly on the Unpaused podcast in April 2026 [4]. She called it the naturalistic fallacy. Her point, which is worth pausing on, is that the cultural assumption that something natural is therefore better is a thought error, not a fact. Dying in childbirth is natural. Wearing socks is not. We do not generally apply natural-is-better logic to anything else in our lives. Yet women in midlife are sold compounded preparations on the grounds of being more natural, and offered judgement when they choose the regulated, well-studied option.

Calling a compounded hormone preparation natural does not make it more like the body's own hormones. Both compounded and TGA-approved body-identical hormones are made from the same plant source and synthesised in the same kind of laboratory. The molecules are identical. What differs is who regulated the manufacturing, how consistent the dose is, and what outcome data exists.

Natural, in this conversation, is a marketing word, not a scientific one. Knowing that changes what you are actually being asked to choose between.

What does "synthetic" mean?

Synthetic hormones used in MHT have a different chemical structure to the hormones the body produces. They are designed to act on the body's hormone receptors but are not chemically identical.

This is not unusual. Many medicines work this way. They sit close to a body molecule, act on the same receptor, and produce a similar effect, but they are not the same molecule. For some drug classes, a body-identical option is never possible. The synthetic version is the only option.

In MHT, both body-identical and synthetic options exist. Synthetic preparations, including those used in the WHI study, remain available and are still prescribed in some circumstances. The current Australian first-line, however, is body-identical.

There is one important reason why this distinction matters most for women. It comes down to what we know about the products from research.

Most of the long-running outcome data we have on MHT comes from studies that used either older synthetic preparations (as in WHI) or, in newer trials, body-identical preparations. Compounded products are not used in clinical trials. So when women read about MHT data, that data refers to TGA-approved or government-approved products, not to compounded preparations. The compounded product a woman is being prescribed has not been part of the safety and efficacy data she may have read about.

What does "bioidentical" mean, and why does this word cause so much confusion?

In the strict scientific meaning of the word, body-identical and bioidentical refer to the same concept. A hormone with the same chemical structure as the body's own. By that scientific definition, the TGA-approved oestradiol patch your GP prescribes is bioidentical.

But in common usage, the two words are now used to differentiate between two very different products, based on regulation and manufacturing.

Body-identical, in Australian practice, always means a TGA-approved pharmaceutical preparation. Manufactured under regulation, with consistent dose, predictable absorption, and decades of safety and outcome data behind it.

Bioidentical, in social media, popular media and some private clinics, often means a compounded bioidentical preparation. Custom-mixed by a compounding pharmacy on the basis of an individual prescription. Bioidentical in molecule, but custom-made. The dose in the cream may not exactly match the dose on the label. Absorption may vary from batch to batch. There is no large-scale safety or efficacy data on the specific compounded product. And in many cases, the woman is paying significantly more for it than she would for a PBS-listed TGA-approved equivalent.

Same word, scientifically. Practically, two very different products.

What is the Australian position on compounded bioidentical hormones?

The Australasian Menopause Society, the Royal Australian and New Zealand College of Obstetricians and Gynaecologists, and Jean Hailes all hold the same position. TGA-approved body-identical hormones are first-line. Compounded bioidentical preparations are not routinely recommended, because of the lack of regulatory oversight on dose accuracy, product purity, and outcome data [5,6,7].

The position is not based on a dislike of bioidentical molecules. The molecules themselves are the same. It is based on how the products are made, regulated, and studied.

Compounded preparations may be considered in certain clinical circumstances, for example when a woman has documented allergic reactions to multiple TGA-approved options, or when a non-standard dose is clinically indicated and not commercially available. In those situations, compounding has a role under specialist supervision, and this is a conversation to raise with your GP rather than a decision to make on the basis of online information.

In simple terms

If you are starting MHT in Australia, the practical questions are:

- Body-identical or synthetic? The modern Australian first-line is body-identical. That means oestradiol (patch, gel or spray) and micronised progesterone (Prometrium).

- One practical note on Prometrium. The capsules contain peanut oil as the suspending agent. Women with a peanut allergy, or a documented reaction to peanut oil, should flag this with their GP. A compounded micronised progesterone without peanut oil may be appropriate in this specific situation [8].

- TGA-approved or compounded? TGA-approved is first-line. Compounded has a narrow specialist role.

The TGA-approved body-identical options available in Australia today are well-studied, well-regulated and what current Australian guidelines recommend as first-line.

Compounded preparations have a narrow specialist place. They are not better, safer or more natural than the TGA-approved options. They are less regulated, less studied, and often more expensive.

When women work with me and they have been quoted hundreds of dollars for a compounded preparation, my first question is always the same. Has anyone explained what compounded actually means, and how it is different from a TGA-approved option that may do the same job, often under PBS? That is the conversation worth having before any prescription is written.

Want the complete picture?

There are three free resources to take this further.

[PLACEHOLDER] Audio guide on body-identical vs bioidentical MHT. A 10-minute audio overview in plain language. menopausehub.com.au/bioidentical-audio (URL to be confirmed).

[PLACEHOLDER] Body-Identical MHT Key Fact Sheet. A one-page reference you can keep or take to your GP. menopausehub.com.au/links (when published).

[PLACEHOLDER] MHT Complete Guide. The full plain-language guide. menopausehub.com.au/links (when published).

Next in the series

The next blog goes into a question that is starting to evolve in specialist menopause practice. If you have had a hysterectomy, you have probably been told you only need oestrogen. The conversation about whether progesterone has roles beyond uterine protection is starting to grow. The next blog walks through what the evidence actually says, and what it does not yet say.

[Link to Blog 5: Progesterone After a Hysterectomy. The Conversation That Is Starting to Change. To be added when blog 5 is published.]

This information is educational only and does not constitute personal medical advice. Always consult a qualified health professional about your individual circumstances.

© 2026 Menopause Hub | Anna Pattison | Former Registered Nurse, Clinical Myotherapist, Menopause Mentor | menopausehub.com.au

CITATIONS

[1] Newson, L. (2019). The dangers of compounded bioidentical hormone replacement therapy. British Journal of General Practice, 69(688), 540-541.

[2] North American Menopause Society. (2020). Bioidentical Hormone Therapy: Custom Compounded versus Government Approved. NAMS MenoNote.

[3] North American Menopause Society. (2020). Bioidentical Hormone Therapy MenoNote. menopause.org

[4] Casperson, K. Quoted in Haver, M.C. (Host). (21 April 2026). Sexual Health, Libido, and Orgasm: What Medicine Missed with Dr. Kelly Casperson. Unpaused podcast.

[5] Australasian Menopause Society. Position Statement on Menopausal Hormone Therapy. menopause.org.au

[6] Royal Australian and New Zealand College of Obstetricians and Gynaecologists. Guidelines on Hormone Therapy. ranzcog.edu.au

[7] Jean Hailes for Women's Health. Bioidentical Hormones. jeanhailes.org.au

[8] Besins Healthcare. Prometrium (micronised progesterone) Australian Product Information.

[9] Del Duca, F., et al. (2025). Legal Considerations in Bioidentical Hormone Replacement Therapy. Clinica Terapeutica, 176 Suppl. 1(2):36-39.

[10] Therapeutic Goods Administration. Compounded medicines, regulatory framework. tga.gov.au

[11] Davis, S.R., Magraith, K. (2023). Practitioner's Toolkit for the Management of the Menopause. Medical Journal of Australia.

[12] Australasian Menopause Society. Information Sheet — Bioidentical Hormones. menopause.org.au