A high percentage of dietary supplements still contained banned ingredients at least six months following a recall by the U.S. Food and Drug Administration (FDA).

About half of all FDA class-I drug recalls since 2004 have involved dietary supplements that featured banned ingredients that could possibly cause adverse medical consequences. Previous studies have also found that even after recalls by the FDA, dietary supplements are still available for purchase. What is not yet clear is whether or not the supplements for sale following FDA recalls are void of the contaminants.

In a new study conducted by Pieter A. Cohen, M.D., of Harvard Medical School, Boston, and colleagues, 9.9 percent of the 274 recalled supplements analyzed met the criteria for inclusion for the study. These supplements were analyzed the same way that the FDA analyzes supplements prior to being approved for human consumption. Supplements were purchased an average of 34.3 months following an FDA recall.

The researchers discovered that at least one pharmaceutical adulterant was found in 66.7 percent of the recalled dietary supplements that were still available to be bought in stores. Supplements remained contaminated in 85 percent of those used specifically for sports enhancement, 67 percent for weight loss, and 20 percent for sexual enhancement.

According to the authors, action by the FDA has not been totally effective in ridding all dangerous adulterated dietary supplements from the marketplace in the US. The authors urge the should government enforce changes to laws to give the FDA more power in order to prevent the sale of such products in the future.

The findings of the study are published in JAMA.