What are bioidentical hormones? – Harvard Health

Published: August, 2006

Many women and health experts continue to struggle with the turnaround in attitude toward hormone therapy in the wake of the Women's Health Initiative (WHI) trial of combined estrogen and progestin (as Prempro) for preventing later-life ills. The trial was stopped early, in 2002, because hormone users had a higher risk of breast cancer, heart disease, stroke, and blood clots. Though the added risks were small, many women and their clinicians concluded they must discontinue hormone therapy. Many of these women found that hot flashes, sleeplessness, and other menopausal symptoms returned with a vengeance.

Hormone therapy is still considered the most effective treatment for symptoms. But women are not rushing back. One concern of health experts is that women are turning to alternatives they think are safer but may not be.

Even before the WHI results came in, many women were looking for something different to relieve hot flashes, night sweats, and vaginal dryness. Some women disliked the side effects of hormone therapy, such as breast tenderness or bleeding. Others worried about estrogen's link with breast cancer. Still others were opposed to taking drugs for symptoms because doing so implies that menopause is a disease rather than a normal life passage. Some women objected to the use of pregnant mares' urine the source of estrogen in oral conjugated equine estrogens (Premarin), the only estrogen tested in the WHI trial.

Many women assume that "natural" hormones would be better or safer but the term "natural" is open to interpretation.

Any product whose principal ingredient has an animal, plant, or mineral source is technically natural. It doesn't matter whether the substance is ground, put into capsules, and sold over the counter or extracted in a laboratory, manufactured by a pharmaceutical company, and made available only by prescription. For example, the soy plant is the source of supplements that some women take to ease menopausal symptoms; it's also used, along with yams, to make the estrogen in the FDA-approved hormone drug Estrace.

But unlike Estrace, soy supplements aren't regulated and haven't been rigorously tested in humans, so we don't know whether they're safe or effective. There's some evidence that certain soy components may actually stimulate breast tumor growth. So "natural" doesn't necessarily equal "safe" and may simply be a euphemism for "unregulated."

The interest in a more natural approach to hormone therapy has focused attention on bioidentical hormones hormones that are identical in molecular structure to the hormones women make in their bodies. They're not found in this form in nature but are made, or synthesized, from a plant chemical extracted from yams and soy. Bioidentical estrogens are 17 beta-estradiol, estrone, and estriol. (Estradiol is the form of estrogen that decreases at menopause.) Bioidentical progesterone is simply progesterone. It's micronized (finely ground) in the laboratory for better absorption in the body.

Bioidentical hormone therapy is often called "natural hormone therapy" because bioidentical hormones act in the body just like the hormones we produce. But here again, that tricky word natural muddies the waters. Pregnant mares' urine is natural, but Premarin is not bioidentical, at least not to human estrogen. The same goes for Cenestin, which is made from plants but is not bioidentical.

Technically, the body can't distinguish bioidentical hormones from the ones your ovaries produce. On a blood test, your total estradiol reflects the bioidentical estradiol you've taken as well as the estradiol your body makes. On the other hand, Premarin is metabolized into various forms of estrogen that aren't measured by standard laboratory tests. Proponents of bioidentical hormones say that one advantage of bioidentical estrogen over Premarin is that estrogen levels can be monitored more precisely and treatment individualized accordingly. Skeptics counter that it hardly matters, because no one knows exactly what hormone levels to aim for, and symptoms, not levels, should be treated and monitored.

Bioidentical estrogens and micronized progesterone are made into a range of products, many of which are FDA-approved and available with a prescription at your local drugstore (see chart, "FDA-approved hormones for menopausal symptoms"). Commercially available bioidentical estradiol comes in several forms, including pill, patch, cream, and various vaginal preparations. Micronized progesterone comes in a capsule or as a vaginal gel.

Type/source

Brand name(s)

Preparations

Bioidentical?

Estrogens

Conjugated equine estrogens (CEE)/pregnant mares' urine

Premarin

PillVaginal cream

NoNo

Synthetic conjugated estrogens/plants

Cenestin, Enjuvia

Pill

No

Esterified estrogens/plants

Menest

Pill

No

17 beta-estradiol/plants(micronized)*

Estrace, others

Pill

Yes**

Alora, Climara, Esclim, Estraderm, Vivelle, others

Patch

Yes

Estrogel

Transdermal gel

Yes

Estrasorb

Topical cream

Yes

Estrace

Vaginal cream+

Yes

Estring

Vaginal ring+

Yes

Estropipate (modified estrone)/plants

Ortho-Est, Ogen, others

Pill

No

Ogen

Vaginal cream+

No

Estradiol acetate

Femring

Vaginal ring

Yes

Estradiol hemihydrate

Vagifem

Vaginal tablet+

Yes

Ethinyl estradiol

Estinyl

Pill

No

Progestins, micronized progesterone

Medroxyprogesterone acetate (MPA)

Amen, Cycrin, Provera

Pill

No

Micronized* progesterone USP

Prometrium

Pill

Yes

Prochieve 4%

Vaginal gel

Yes

Norgestrel

Ovrette

Pill

No

Norethindrone

Micronor, Nor-QD, others

Pill

No

Norethindrone acetate

Aygestin, others

Pill

No

Combined hormones

CEE and MPA

Premphase, Prempro

Pill

No

Ethinyl estradiol and norethindrone acetate

Femhrt

Pill

No

17 beta-estradiol and norethindrone acetate

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What are bioidentical hormones? - Harvard Health