Over half of major drug recalls in the United States over the past decade involved dietary supplements that contained unapproved ingredients.

The US Food and Drug Administration also warned that dietary supplements which contained a stimulant called dimethylamylamine (DMAA) posed a serious health risk to its consumers and added that such products have been banned in the US.
The agency added that DMAA products have been linked to around 60 deaths or illness, including heart problems and nervous system or psychiatric disorders.
Source-Medindia