(CBS News) A new report may have a lot of people checking the labels on the dietary supplements they take. These supplements are big business with sales topping $30 billion last year. About 84 percent of Americans use them. But in many cases, there's no way to know if they work.
Wednesday's report found that 20 percent of supplements had labels that claimed to treat a disease -- and that's illegal.
For example, the government says a label for a product containing vitamins and a compound called "DIM complex" is legal, because it claims to boost the immune system and support overall health -- but does not say it treats a specific disease.
Another label for a product containing algae and an herb called "heal-all" is illegal because it claims to treat diseases including herpes and the flu.
"This report raises questions about the extent to which these claims are truthful and not misleading," said lead analyst Melissa Haffner, "because the FDA doesn't have the ability to look at the substantiation behind the claims. There is really no way for them or consumers to know whether or not the claims are truthful."
The FDA has only limited power to regulate supplements because federal law classifies them as food, not drugs. Products are required to be safe, but the FDA only monitors them after they're on the market.
When it comes to proof, supplement makers are only required to say research has been done. They are not required to show it to the FDA.
The Natural Products Association, the main trade group of the supplement industry, issued a statement saying: "This small sample of supplements shouldn't smear the entire industry."
The investigators looked at 127 supplements that claim to boost the immune system or help with weight loss. None met all of the FDA's recommendations for proving the products actually worked.