The most widely sold brands of hormone therapy are made from conjugated equine estrogen (taken from the urine of pregnant horses), manufactured either alone or with the addition of a ­progesterone-type formulation known as progestin. Some women resist taking these kinds of chemicals and feel that it is more natural to use bio­identical hormones—ones that are an exact molecular match for those that ­occur in the body. In some cases, bioidentical versions may cause fewer side effects. For instance, women who take bio­identical progesterone may experience less bloating, breast tenderness and moodiness and fewer headaches than they would with progestin. Research is limited, and so far no one has shown that long-term use of bio­identicals ­carries fewer health risks than conventional pills do.

Bioidenticals come in the two forms described here. Most doctors are fine with the first, but the second makes many of them nervous:

1. Drugs approved by the FDA, manufactured by a pharmaceutical company and sold at regular pharmacies. The category includes estradiol patches and micronized oral progesterone; you might take one or both. “They’re closer to the real thing than what’s in conjugated estrogen and synthetic progestin,” says JoAnn Manson, MD, president of the North American Menopause Society. But micronized progestin is often made with peanut oil and is not suitable for women who are allergic to peanuts.

2. Custom-compounded bioidentical hormones (estradiol and progesterone), which are not FDA approved. Based on a prescription from a doctor who tests your hormone levels, the bioidentical ingredients are mixed by specialized pharmacies. “The oversight of these products is not as rigorous as with FDA-approved ones. There’s concern about contamination and inconsistency of doses,” Manson says.

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