Bioidentical hormones: what the term means, and what the evidence says

“Bioidentical” describes hormones that are chemically identical to the ones your body makes. Many FDA-approved products already fit that description, including estradiol patches, gels and pills and micronized progesterone capsules. In marketing, though, the word usually means custom-compounded hormones mixed by a pharmacy, which are not FDA-approved, are not required to prove consistent doses, and have no evidence of being safer than approved hormone therapy.

Two different things share one name

The Menopause Society’s 2022 position statement calls the term misleading for exactly this reason: there are government-approved bioidentical hormones and compounded ones, and they are regulated very differently.

	FDA-approved bioidentical hormones	Compounded “bioidentical” hormones
Examples	Estradiol (pills, patches, gels, sprays, vaginal products); micronized progesterone capsules	Custom creams, capsules, troches and pellets, sometimes mixing estradiol, estrone, estriol, progesterone, DHEA and testosterone
FDA review of safety and effectiveness	Yes	No
Dose accuracy	Regulated and monitored for purity and efficacy	Variable; in one study, up to 26% below label for estradiol and 31% above for progesterone
Package insert listing risks	Required	Not required
Evidence	Randomized trials	Mostly small, short, uncontrolled studies
How doses are set	By symptom response	Often by saliva, urine or blood tests, which guidelines call unreliable

What “bioidentical” does and does not tell you

ACOG defines bioidentical hormones as plant-derived hormones that are chemically similar or structurally identical to those the body produces. That description covers FDA-approved micronized progesterone, whose label states it is synthesized from a plant starting material and is chemically identical to ovarian progesterone. It also covers prescription estradiol, which The Menopause Society notes is identical to the estradiol the ovaries make.

Two common hormone therapy ingredients are not bioidentical: conjugated equine estrogens, used in the Women’s Health Initiative, and synthetic progestins such as medroxyprogesterone acetate. If avoiding them is your goal, you can do that entirely with FDA-approved products; see progesterone vs progestin. “Plant-derived” also does not distinguish compounded products, because approved products start from plant sources too.

How common compounded hormones are

Two US surveys published in 2015 estimated that 1 million to 2.5 million women aged 40 and older use compounded hormone therapy, accounting for 28 to 68 percent of hormone therapy prescriptions. Eighty-six percent of women in one of the surveys did not know compounded products are not FDA-approved. The National Academies of Sciences, Engineering, and Medicine (NASEM), in a 2020 report commissioned by the FDA, estimated that compounded hormone preparations for men and women account for 26 to 33 million prescriptions, costing more than $2 billion a year.

NASEM also looked at why people choose them. Factors included the way the WHI results were first communicated, boxed warnings on FDA-approved products, marketing, mistrust of the drug industry, interest in “natural” treatment, and cost.

What the evidence shows

On effectiveness and safety. NASEM found a lack of rigorous evidence from well-designed trials; information on compounded hormones came mostly from anecdotes, patient reports and prescriber testimonials. ACOG’s 2023 clinical consensus adds that most studies were uncontrolled, lasted less than a year and measured surrogate markers. Controls matter in menopause research: ACOG points out that in a Cochrane review, hot flashes fell by 57.7 percent on placebo alone. ACOG found the data inadequate to judge the risk of breast cancer, endometrial cancer or heart disease with compounded products.

On dose. In an analysis ACOG cites of estradiol and progesterone capsules and creams from 13 compounding pharmacies, most products were within 10 percent of the labeled amount, but some had up to 26 percent less estradiol or 31 percent more progesterone than stated. ACOG also notes the potential for bacterial contamination. Underdosing progesterone matters: if it does not protect the uterine lining, estrogen can cause overgrowth. Our guide to micronized progesterone explains why progesterone creams do not provide that protection.

On estriol. The FDA says there are no FDA-approved drugs containing estriol and that it has no evidence estriol is a “safer form of estrogen.”

Pellets

Hormone pellets are implanted under the skin and release hormone over months. ACOG notes they are not designed to be removed and are generally reinserted every 3 to 6 months, so exposure cannot be stopped quickly. NASEM found that estradiol and progesterone pellets exist only as compounded products and recommended that all compounded pellets be reviewed as candidates for the FDA’s Difficult to Compound List. ACOG recommends forms other than pellets for women who use testosterone.

Testing to “customize” doses

Compounded regimens are often dosed by saliva, urine or blood hormone levels. The Menopause Society calls salivary and urine testing for dosing unreliable and not recommended, and says serum testing is rarely needed, because absorption and daily rhythms vary within and between women. ACOG notes there are no FDA-approved salivary or urinary tests for steroid hormones and advises adjusting doses to symptom relief.

When compounding is reasonable

NASEM recommended restricting compounded hormones to two situations: a documented allergy to an ingredient in an FDA-approved product, or a documented need for a dosage form that is not available. A peanut allergy, which rules out progesterone capsules made with peanut oil, is a commonly cited example. The Menopause Society and NASEM both say patient preference alone should not justify compounding. Testosterone for women is a separate case, because no FDA-approved product exists; see our guide on testosterone and libido.

The label change and the “safer” argument

Part of the appeal of compounded hormones has been that they arrive without the frightening boxed warning printed on approved products. Since the FDA’s November 2025 action, cardiovascular disease, breast cancer and dementia have been removed from that warning, as explained in Is hormone therapy safe?. A compounded product carries no warning because it is not required to have a full label, not because it has been shown to be safer; NASEM in fact recommended that compounded estrogen and testosterone products carry boxed warnings like those on approved products. The FDA continues to recommend FDA-approved hormone therapy.

If you are offered compounded hormones

• Is there an FDA-approved product with the same hormone and route?
• What is the documented reason compounding is needed for me?
• Exactly which hormones are in it, at what doses?
• How is the dose verified, and how will we monitor my uterine lining?

Our guide on how to talk to your doctor about hormone therapy covers what to do next, and our OB-GYN directory can help you find a second opinion.