The findings were disappointing news for women seeking alternatives to estrogen-progestin hormone supplements, which have been linked to breast cancer and heart problems.
The yearlong study of 351 women suffering from hot flashes and night sweats found that those given black cohosh got about the same amount of relief as those who took a placebo. And those groups saw nothing close to the improvement in women on hormones.
"It's disappointing news," said Katherine Newton, an epidemiologist who helped lead the study, funded by the National Institute on Aging and the National Center for Complementary and Alternative Medicine. "It would be nice to offer something safe and effective."
The study was conducted at Seattle-based Group Health, a health plan, and was published Monday in the Annals of Internal Medicine.
Black cohosh — an herb that is a member of the buttercup family and is commonly given to ease menopause symptoms — is available in pill or liquid form and is sold over the counter in many health food stores and over the Internet.
It is among a host of supplements including soy, wild yam, red clover and St. John's wort that have been tried for relief of hot flashes and night sweats, but studies almost universally have found they don't work.
Certain antidepressants have proved effective, and one company, Depomed Inc. of Menlo Park, Calif., plans to seek the Food and Drug Administration's approval to sell an anti-seizure drug, gabapentin, for relief of hot flashes.
In the latest study, some participants were given black cohosh, while others received hormone supplements, a placebo or a botanical treatment that included black cohosh, alfalfa, licorice and ginseng.
Women taking the herbal treatments saw hot flashes reduced by only about half an episode per day compared with those taking the placebo, the study found. Those who got hormone therapy reduced their hot flashes by about four episodes per day when compared with the placebo.
Menopausal women can still make behavioral changes such as dressing in layers, sleeping in a cooler room and avoiding possible triggers such as very hot liquids and alcohol, Newton said. The study also shows that symptoms decreased over the course of the 12-month period and that they nearly always go away on their own.
The findings come less than a week after researchers reported a dramatic decline in U.S. breast cancer cases, a drop doctors attributed partially to fewer women using hormone therapy to treat menopause.
In 2002, a government study found a higher risk of breast cancer and heart problems occurred among women taking estrogen-progestin pills. Millions of women stopped taking the supplements. Doctors urged women with serious menopausal symptoms to use the lowest dose for as short a time as possible.
The latest study, conducted between 2001 and 2004, could hurt hopes for herbal remedies.
"We hope that this is not it," said Dr. Susan Reed, another of the study's authors. "However, there's not much that appears promising that is currently on the horizon."
The news may not all be bad. Since women who took a placebo saw some improvement, experts say there is hope that some could get relief through meditation or self-hypnosis.
"If you can relax your mind appropriately, you can also relax your body," said Barrie Cassileth, an alternative-medicine researcher at Memorial Sloan-Kettering Cancer Center in New York, who was not involved in the study. "If 30 percent of women could lose hot flashes because their mind made them do it, that's fantastic."