Bioidentical vs Synthetic Hormones for Perimenopause: What Is the Real Difference?
Bioidentical and synthetic hormones are both used in perimenopause treatment. Here is what the evidence says about safety, effectiveness, and marketing claims.
What Does Bioidentical Actually Mean?
The term bioidentical refers to hormones that are chemically identical in structure to the hormones produced naturally by the human body. Bioidentical estradiol, for example, has the same molecular structure as the estradiol your ovaries produce. The same applies to bioidentical progesterone. This is distinct from synthetic hormones, which may have a similar but not identical chemical structure to natural hormones. The confusion in this area is significant because the term bioidentical is used in two very different contexts. Regulated, licensed HRT medications including many standard NHS prescriptions use bioidentical hormones. And separately, compounding pharmacies offer unregulated custom-mixed bioidentical hormone preparations. These two things are very different in terms of quality, safety, and evidence base.
Regulated Bioidentical HRT on the NHS
Many standard HRT products prescribed on the NHS already contain bioidentical hormones. Estradiol patches, gels, and sprays all use bioidentical estradiol. Utrogestan (micronised progesterone) is a bioidentical progesterone capsule that is now widely recommended because of its favourable safety profile. These products have been rigorously tested in clinical trials, are manufactured to pharmaceutical standards, contain consistent doses, and are regulated by bodies such as the MHRA in the UK. When clinicians and researchers refer to evidence supporting the safety and effectiveness of HRT, this regulated bioidentical HRT is what they are talking about. Choosing these options means you are getting bioidentical hormones backed by evidence.
Compounded Bioidentical Hormones: What to Know
Compounded bioidentical hormone preparations (often called BHRT) are custom-mixed by compounding pharmacies, sometimes based on saliva testing and without standard pharmaceutical oversight. They are marketed heavily as natural and personalised alternatives to conventional HRT. However, the evidence base for compounded BHRT is significantly weaker than for regulated HRT. Concerns include inconsistent dosing (the amount of hormone in each preparation may vary from batch to batch), lack of rigorous clinical trials, and the use of routes of administration such as subcutaneous pellets that have not been evaluated as thoroughly for safety. Menopause specialist societies in the UK, US, and Europe have issued guidance cautioning against compounded BHRT as a first-line option, not because bioidentical hormones are unsafe, but because the compounding process introduces quality and consistency risks.
Synthetic Progestogens: The Real Comparison Point
Where the bioidentical versus synthetic distinction matters most clinically is in the progesterone component of HRT. Older HRT preparations used synthetic progestogens, such as medroxyprogesterone acetate (MPA) and norethisterone. Some studies, including parts of the Women's Health Initiative, found elevated breast cancer risk associated with combined HRT using MPA. More recent evidence and updated analyses suggest that micronised progesterone (bioidentical) carries a lower breast cancer risk than synthetic progestogens. This has led to a significant shift in UK prescribing guidance toward body-identical progesterone. The distinction between micronised progesterone and synthetic progestogens is a meaningful clinical one, unlike the broader marketing use of the term bioidentical.
Saliva Testing and Personalised BHRT
Compounded BHRT is often sold alongside saliva hormone testing, with preparations tailored to individual test results. The idea of personalised hormone therapy sounds appealing, but saliva testing for hormone levels is not considered a reliable diagnostic tool by mainstream endocrinology and menopause specialists. Hormone levels fluctuate throughout the day and across the menstrual cycle, and saliva tests capture a single snapshot that may not reflect clinical need accurately. Standard blood tests ordered by a qualified clinician are a more reliable basis for prescribing decisions. If a practitioner is primarily offering saliva testing and custom compounded hormones without engaging with your full medical history, it is worth seeking a second opinion from a specialist with recognised menopause training.
Cost and Availability
Regulated bioidentical HRT products are available on NHS prescription in the UK at standard prescription charges, or free for those with prescription exemptions. They are also available privately at modest cost. Compounded BHRT from private clinics and compounding pharmacies is typically significantly more expensive, often running to hundreds of pounds per month. Given that the evidence for compounded preparations is weaker rather than stronger, the higher cost does not reflect a higher standard of care. For most women, regulated bioidentical HRT on the NHS represents the most evidence-backed and cost-effective option.
Making an Informed Choice
If you are drawn to bioidentical hormones because of concerns about the safety of conventional HRT, it is worth knowing that regulated NHS HRT already includes bioidentical options. Estradiol patches, gels, and micronised progesterone are all bioidentical, well-studied, and widely prescribed. The choice between these and compounded alternatives is not a choice between natural and synthetic, it is a choice between well-regulated and less-regulated. Discuss your concerns openly with a GP or menopause specialist, ask specifically about body-identical estradiol and micronised progesterone, and make decisions based on the evidence available rather than marketing language.
Related reading
Get your personalized daily plan
Track symptoms, match workouts to your day type, and build a routine that adapts with you through every phase of perimenopause.