When night sweats, hot flashes and other signs of menopause come to call, many women find themselves desperate to soothe their symptoms. For some, the search for relief will lead them to consider bioidentical hormone therapy, a treatment that has been popularized by such celebrities as Suzanne Somers and Oprah Winfrey. Proponents say bioidentical hormones are natural, effective and safe, but is that true?

To answer that question, you have to start with some definitions, says JoAnn Manson, a professor of medicine at Harvard Medical School and chief of preventive medicine for Boston’s Brigham and Women’s Hospital.

“There are several misconceptions about hormones and hormone therapy,” Manson says — starting with what exactly hormone therapy is.

As women age, the key hormones their bodies naturally produce — estrogen, which is a group of hormones that includes estriol, estradiol and estrone, as well as progesterone and testosterone — may fluctuate or decline. These hormonal changes can trigger a range of troublesome symptoms, ranging from vaginal dryness to mood changes and the hot flashes so many women dread.

Any kind of hormone therapy aims to ease symptoms by putting back some of those lost hormones.

Conventional hormone therapy — the kind that was widely prescribed between the 1960s and the early 2000s — supplies synthetic versions of the lost estrogen and progesterone that are slightly different on the molecular level from what a woman’s body makes but perform many of the same functions. These hormones developed a bad reputation after the Women’s Health Initiative, a study that followed nearly 30,000 women over several years as they took either estrogen alone or estrogen and progesterone together, found that the synthetic hormones increased the risk of heart attack, blood clots, breast cancer, dementia and stroke. The results were so dramatic that the study was ended three years early, in 2002, to protect the participants’ health.

It was after WHI released its first results that interest in bioidentical hormones, which had been around for decades but never in the mainstream, began to surge, says Adriane Fugh-Berman, an associate professor of pharmacology and physiology at Georgetown University Medical Center. Like conventional hormones, bioidentical or human-identical hormones are synthetic, derived from a chemical found in soy and yams. But they share the molecular structure of naturally occurring hormones.

“ ‘Bioidentical’ is not a scientific term,” Fugh-Berman says. “It just means they have the same chemical structure as the hormones your body makes.”

Because they match the body’s own hormones, bioidentical hormones have been touted as a natural, safe alternative to conventional hormone therapy, Fugh-Berman says — and this is where misconceptions again come into play.

Many women have gotten the impression that bioidentical hormones are “natural” and not synthetic because of their plant derivation, says Erika Schwartz, founding director of the Bioidentical Hormone Initiative, which promotes their use.

“But they’re all synthetic, because you need a pharmaceutical company to manufacture them,” she says. Pharmaceutical companies tweak the plant-derived molecules to match the chemical structure of human hormones.

Many commonly prescribed conventional hormones are also derived from natural sources — including pregnant mare urine — and then synthesized into their commercial forms in laboratories.

Another common misconception, Manson says, is that bioidentical hormones are available only from compounding pharmacies, which combine pharmaceutical ingredients into custom-made medications. Compounding pharmacies have been controversial since last year’s outbreak of fungal meningitis that killed 55 people was traced by to a single compounding center. But bioidentical hormones need not be custom-mixed: They’re available in FDA-approved pills, creams and patches. (Two popular brans are Estrace and Estraderm). Manson says that she shies away from compounded medicines because they are not FDA-approved but that on occasion they can be useful.

“If a woman has an allergy to an ingredient in a commercially available product — such as peanut oil, which is used in FDA-approved bioidentical progesterone — then she may want to use a custom-compounded product,” Manson says. “Otherwise, there are very few reasons to go the custom- compounding route.”

Compounded or not, the greatest source of controversy and confusion regarding bioidentical hormones is the claim of greater safety.

“There’s this misconception that if a chemical is the same as the chemical your body makes, it must be good for you,” Fugh-Berman says. “But we know that too much of your homegrown hormones can cause problems, too. We know, for example, that women with naturally high estrogen levels run a higher risk of breast cancer and that men with high testosterone have a higher risk of prostate cancer. Consumers should not think that natural is safer.”

There’s some evidence that going bioidentical for progesterone, at least, carries benefits. Fugh-Berman notes that a 2008 study of more than 80,000 French women found that while combining estrogens (including bioidentical estradiol) with conventional synthetic progesterone significantly increased breast cancer risk, combining them with bioidentical progesterone did not. But Fugh-Berman points to a number of studies, including a 1999 Swedish study of bioidentical estriol that found that taking estriol orally raised the risk of endometrial cancer and a 2001 study showing higher risk of fatal stroke among women taking bioidentical estradiol, as evidence that bioidentical estrogens carry risks, too.

“We have enough supporting evidence to know the risks are the same,” Fugh-Berman says. She says women who are struggling with severe menopausal symptoms should feel free to choose bioidentical hormones but should do so after talking to their doctor about possible risks. “If you’re having terrible hot flashes and you choose to use bioidentical hormones, that’s fine. Just don’t think they carry fewer risks.”

Schwartz, who has used bioidentical hormones herself for the past 16 years, disagrees about the risks, however. She says she has seen, in herself and her patients, that women respond well to bioidentical hormones.

Women seeking relief should work with a medical professional to find a solution that feels right for them, she says.“We’re forgetting about quality of life in our health care,” Schwartz says. “That’s the real tragedy here.”