The finding — and an unrelated study suggesting that magnetic heel insoles are ineffective at relieving pain — question the marketing practices of widely popular alternative medical products.
An editorial published with the studies in Wednesday's Journal of the American Medical Association said improvements are needed in the regulation of alternative treatments.
In one study, Drs. Charles Morris and Jerry Avorn of Boston's Brigham and Women's Hospital analyzed Internet marketing claims of eight popular items, including St. John's wort for depression, echinacea for infections and ginseng for stress. Such products are used by an estimated 14 percent of U.S. adults, according to data cited in the study.
Of the 443 Web sites examined, 292 made health claims for their products, such as claiming they could cure, prevent or treat a disease. More than half of those, or 153, omitted a federally required disclaimer saying that the claims had not been evaluated by the Food and Drug Administration and that the products are not intended to treat or prevent disease.
On 39 percent of the sites for the herb kava kava, no information was listed about an FDA advisory linking the products with liver problems.
Unlike prescription drug makers, herbal products manufacturers can make health claims in marketing that are not supported by science.
The findings show that system is not effective and bolster the argument for having one system for both herbs and drugs, Drs. Catherine De Angelis and Phil Fontanarosa, JAMA's editor and executive deputy editor, said in the accompanying commentary.
The Council for Responsible Nutrition, a trade group for dietary supplement makers, advises members not to make unsubstantiated claims and tells them to disclose "any adverse event information," said Annette Dickenson, group president.
She said the study should not lead people into thinking all such products are ineffective. "There are proven benefits of many of the botanical products and consumers want to know that," Dickinson said.
The other study, from the Mayo Clinic, casts doubt on the health claims of products containing magnets as purported pain relievers. It involved 101 volunteers with heel pain who wore either heel insoles with magnets or insoles with fake magnets for eight weeks.
At the study's end, about a third of patients in each group reported pain relief.
Spenco Medical Corp., manufacturer of the insoles used in the study, no longer makes magnetic products, said a company spokeswoman who declined further comment.