Bioidentical HRT vs Synthetic HRT: What Is the Difference?

What the Terms Actually Mean

Bioidentical hormones have the same molecular structure as the hormones your body produces naturally. Synthetic hormones are chemically altered versions that act on the same receptors but have a different molecular shape. Both categories include regulated pharmaceutical products. The term 'bioidentical' is also used by some compounding pharmacies for custom-mixed formulas, which is a separate and less regulated category.

Regulated Bioidentical HRT

Body-identical or regulated bioidentical HRT includes estradiol patches, gels, sprays, and micronised progesterone capsules like Utrogestan. These are approved, standardised, and tested for safety and efficacy. Micronised progesterone, in particular, is increasingly preferred by menopause specialists because it appears to carry a lower risk of blood clots and may have a more favourable breast cancer risk profile compared to some synthetic progestogens.

Synthetic HRT

Synthetic progestogens like norethisterone and medroxyprogesterone acetate have been used in HRT for decades. They are effective at protecting the uterine lining when used alongside estrogen. However, some research has associated certain synthetic progestogens with a slightly higher breast cancer risk and a greater risk of blood clots compared to micronised progesterone. That said, they remain safe and appropriate for many women, and the absolute risks involved are still small.

Compounded Bioidentical HRT

Compounded bioidentical HRT is custom-made by specialist pharmacies, often based on saliva hormone testing. Most menopause guidelines do not recommend compounded HRT as a first-line approach because dosing is not standardised, safety data is limited, and saliva testing is not a reliable guide to hormone levels. It may have a role in very specific circumstances, but it should be discussed carefully with a doctor rather than sought independently.

Which Is Better?

For most women, regulated body-identical HRT using estradiol and micronised progesterone represents the current gold standard recommended by menopause specialists. It is not that synthetic HRT is unsafe; it is that the evidence base for body-identical options has grown substantially over the past decade. If you are currently on a synthetic preparation and it is working well for you, there may be no urgent reason to switch. But it is worth discussing options at your next review.

Talking to Your Doctor