Dietary supplement industry, worth billions, operates freely with minimal oversight from the U.S. Food and Drug Administration. Former FDA research scientist claims that around one in four dietary supplements don't meet quality and safety standards.

Some of the supplements get tainted with pesticides, salmonella, glass, bacteria or heavy metals while others lack ingredients, have improper ingredients or fail to disintegrate properly.

Federal law from 1994 says that dietary supplements don't need to be approved by the FDA. There aren’t even set minimal standards for the safe manufacture of dietary supplements. Low cost ingredients are often imported from China and some may be tainted. Manufacturers are left to set their own standards and are help responsible for their products safety. Also, they don't have to record, review or provide the FDA with reported injuries or illnesses that result from their products.
If problems related to the safety or mislabeling occur, the FDA has the right to remove this product from the market.

Back in 1997, the FDA proposed mandatory rules outlining "good manufacturing practices" for the safe production of dietary supplements; however those rules haven't still been finalized.

The biggest concern of the supplement makers seems to be that the new safety proposals would cost the industry $245 million a year, 10 times more than the FDA estimated.