Americans spent $14.8 billion in 2007 on herbal supplements and other natural health products, even though numerous recent studies have shown that ginkgo, echinacea, St. John’s wort and others are relatively ineffective against many of the ills they have claimed to help. A recent investigation by the Government Accountability Office, part of which employed undercover senior citizens, has revealed how loose regulations and questionable sales tactics are more persuasive than science, potentially putting consumers’ health at risk.

The U.S. Food and Drug Administration regulates all dietary supplements as food products under the 1994 Dietary Supplement Health and Education Act, which says that the manufacturers are only responsible for making sure a supplement is safe and meets efficacy claims. But supplement makers are not required to present any information about how they arrived at these conclusions. And although makers cannot claim a product will cure, treat or prevent a specific condition, labels on their products can boast of general body function improvements, such as “aids digestion,” “improves heart health” or “boosts brain function,” says Paul G. Shekelle, an internist and director of the Southern California Evidence-Based Practice Center at RAND.

These label claims must be followed by a standard FDA disclaimer, but people often do not get the right message, Shekelle says. He notes that “those distinctions can be confusing to consumers,” who often might not have all the information to separate body-function statements (“boosts brain function”) from specific treatment indications that they might be seeking (“prevents Alzheimer’s”).

Moreover, messages can get mixed when a sales associate steps in to interpret claims for consumers. The GAO sent undercover staff members to ask common questions of supplement retailers, using consumers over the age of 65 because most of them take prescription medication with which a supplement could interact. The seniors’ inquiries included: Is ginkgo biloba safe to take with aspirin? Can ginseng fend off cancer? What about replacing prescribed blood pressure medication with garlic supplements?

The queries got resounding yes’s from supplement sales staffs, the GAO found—but they are big no’s per the National Institutes of Health. A combination of ginkgo and aspirin can increase the risk of internal bleeding. Ginseng has not been scientifically proved to cure any diseases and should be avoided for those with breast and uterine cancers, according to the NIH. Garlic has not been shown to significantly lower high blood pressure—and supplements are not intended to replace prescribed drugs.

The statements by supplement sales staff amount to “unequivocal deception,” argues Marcus M. Reidenberg, chief of the division of clinical pharmacology at New York–Presbyterian Hospital/Weill Cornell Medical Center. Both the FDA and the Federal Trade Commission found the practices “improper and likely in violation of statutes and regulations,” stated the GAO report, which was delivered as testimony to Congress on May 26.

The supplement industry’s defense came from Steve Mister, president and chief executive officer of the Council for Responsible Nutrition, one of several supplement trade groups. In congressional testimony, he noted that “making false or misleading statements about a dietary supplement in a consumer transaction violates many states’ consumer protection, antifraud and unfair competition statutes.” He also added that he was not sure “whether the retailers in the GAO’s investigations are aware that they are breaking the law.”

As Shekelle sees it, the big question is not whether customers should want to spend their money on products of questionable efficacy but whether “taking this stuff is going to be deleterious to their health.” Of the 40 herbal supplements tested for the GAO investigation, 37 contained trace levels of at least one hazardous compound. Other analyses have found contaminants that include steroids and even active pharmaceuticals, Shekelle points out. “This goes back to the presumption that dietary supplements are safe,” he says.

To be sure, the contaminants and questionable marketing practices are no surprise to those who have followed this topic in recent years. But the GAO report gives new weight to the issue, which is likely to come up in any congressional debate on food safety. The supplement industry will probably fight additional regulation, which Mister called burdensome, noting that the industry associations have stepped up their efforts to improve inspection and regulation of member companies.