Certain dietary supplements were deceptively or questionably marketed, said the Government Accountability Office (GAO) in a report. The report also said that 37 of the 40 herbal dietary supplement products tested by the GAO contained trace amounts of at least 1 potentially hazardous contaminant (such as lead, mercury, or arsenic), although none of them in amounts considered to pose an acute toxicity hazard (http://www.gao.gov/new.items/d10662t.pdf).
Mitka M. Supplements Scrutinized. JAMA. 2010;304(2):148. doi:10.1001/jama.2010.877