The new findings are concerning because they suggest that, even when the FDA tests supplements and discovers prohibited ingredients, the agency doesn't always remove these dangerous products, said Dr. Pieter Cohen, an assistant professor of medicine at Harvard Medical School and a general internist at Cambridge Health Alliance in Boston.
"What's the point of identifying products [with prohibited drugs] if you can't take them off the marketplace?
, who was not involved in the new study.
The recalls described in the new study are voluntary, meaning the FDA
asked the manufacturer to recall the product but did not mandate it.
It's not clear why 110 products were found to contain drugs but were not recalled, Cohen
One possibility, Cohen
said, is that the FDA
couldn't get in touch with the manufacturer.
Indeed, a recent investigation by the Office of the Inspector General found that the FDA
did not have accurate contact information for 20 percent of the supplement manufacturers.
It's also possible the FDA
contacted the manufacturer, but the manufacturer refused to comply, Cohen
"The consumer is flying blind when it comes to purchasing supplements," Cohen
Until manufacturers follow the law - and the FDA
enforces it - "these huge categories of supplements need to be completely avoided," he
A 2011 study by Cohen
colleagues found that even supplements that are recalled can still be bought by consumers.
The study found that the weight-loss supplement Pai You Guo, which was recalled in 2009 because it contained a banned drug, could still be bought at retail stores.
lab recently tested a sexual-enhancement drug and found it contained pharmaceuticals.
Even though the lab alerted the FDA
about the supplement - called Sex Plus - in December 2012, the FDA
has yet to warn consumers about it, Cohen
The dietary supplements that are tested and recalled by the FDA
are likely just "the tip of the iceberg," in terms of the percentage of supplements that contain prohibited drugs, Cohen
Consumers who want to buy supplements should stick with vitamins and minerals, or single-ingredient supplements, Cohen
They should look for supplements that have been certified by the U.S. Pharmacopeial Convention or NSF International, which can provide reassurance that the products contain the proper dosage of ingredients and that they don't contain illegal ingredients, Cohen