The report, released in conjunction with today's Senate committee hearing on dietary supplements and the elderly, revealed the results of an investigation in which GAO investigators posed as elderly customers to ask sales staffers at 22 storefront and mail-order retailers about herbal dietary supplements. The GAO also reviewed marketing claims made on 30 retail websites.
Investigators found that sales people gave them "potentially dangerous advice," such as suggesting that they could take supplements instead of prescription medication, according to the report.
"What a lot of people do is ... they start taking both at the same time and then slowly you will stop taking the other prescription medicine and just continue with this," said one seller on an audio recording made by the GAO.
A seller during another GAO sales call said that a combination supplements can prevent or cure serious conditions.
"My mom and dad both have high cholesterol and problems maintaining blood pressure; I don't have either one, but my parents have both. If I wouldn't have started taking my product ... I would eventually get it, because it's in my genes," the seller told the GAO.
When the GAO repeated the false information back, the seller once again claimed it was true.
In some cases, the promises were not just false, they were dangerous. One herbal supplement seller said that a customer could take Ginkgo biloba with aspirin to improve memory.
"In making these claims, sellers put the health of consumers at risk," Greg Kurtz, head of the GAO Forensic Audits and Special Investigations unit, said in remarks prepared for the committee hearing.
The GAO also listed what it called deceptive claims made by herbal supplement marketers tied to Ginkgo biloba and other popular supplements as ginseng, including assertions that the latter can cure cancer and that the former can treat both impotence and Alzheimer's disease.
Steve Mister, the president and CEO of the Council for Responsible Nutrition, a trade association for supplement manufacturers and ingredient suppliers, defended the industry in an interview with ABCNews.com.
"We understand that there are going to be examples of a few industry outliers who may be violating the law, but that is certainly not representative for the vast majority of the industry which is abiding by the law," he said.
Mister, who said Tuesday that he had not yet seen the GAO report, was scheduled to testify at today's hearing.
Mister said that the council has committed $1.5 million for an eight-year program at the Better Business Bureau's National Advertising Division to scrutinize supplement advertising and issue decisions on when supplement sellers should change or pull advertising claims. When a company ignores a National Advertising Division decision, the division refers the ads in question to the Federal Trade Commission.
"This is a good example of industry trying to police itself," he said.