Body-identical HRT: what the term really means

Why the word exists

Older HRT preparations used hormones that were not structurally identical to human ones: conjugated oestrogens derived from animal sources, and synthetic progestogens. They worked, but the body does not handle them in exactly the same way, and some of the risk associated with older HRT relates to those differences.

Modern UK prescribing has largely moved to body-identical preparations. "Body-identical" is the term that distinguishes them.

Body-identical is not the same as "bioidentical"

This is the distinction that matters most, and the words are close enough to be genuinely confusing.

Body-identical hormones are regulated pharmaceutical products. They are made to a consistent standard, licensed by the MHRA, tested, and prescribed at known doses. Micronised progesterone is chemically and structurally identical to human progesterone, and micronisation allows steady, even absorption.

Compounded bioidentical hormones, sometimes marketed as cBHRT, are custom preparations mixed by compounding pharmacies, often based on saliva or blood tests, and frequently sold with claims about being individually tailored or more natural.

UK professional bodies do not recommend compounded bioidentical preparations. The reasons are practical rather than ideological: the preparations are not regulated in the same way, the doses are not verified batch to batch, they have not been through the same testing, and there is no good evidence that individualised compounding based on hormone level testing improves outcomes.

There is a particular concern about endometrial protection. If the progesterone content of a compounded preparation is not reliable, the protection of the womb lining is not reliable either, and that is the risk that matters most.

What "natural" means here, and does not

Body-identical hormones are typically derived from plant sources, usually yam or soy, then converted in a laboratory into the exact human molecule.

So they are plant-derived and laboratory-made and structurally identical to yours, all at once. "Natural" is not a useful word for sorting this, and it is used heavily in marketing precisely because it does not mean anything specific.

What matters is the molecule and the regulation, not the origin story.

What this looks like in practice

A typical modern UK regime is body-identical throughout: estradiol delivered through the skin as a patch or gel, with micronised progesterone as a capsule if you still have a womb.

The evidence position is more favourable than for older preparations. Transdermal estradiol is not associated with the increased clot risk seen with oral oestrogen, and a meta-analysis has found oestrogen combined with micronised progesterone is not associated with increased breast cancer risk in the first five years.

What fira prescribes

Body-identical HRT: estradiol as a patch or capsule, micronised progesterone where you have a womb, and vaginal oestrogen where it is clinically needed.

We do not compound anything, we do not sell bespoke preparations, and we do not base prescribing on saliva hormone testing. Medicines are dispensed by a UK-registered pharmacy in the manufacturer's own pack.

If you are currently on a compounded preparation and want to move to regulated treatment, that is a common reason women come to us, and the assessment starts from where you are.