Researcher Steven Newmaster of University of Guelph was astounded to find 60% of randomly selected supplements he tested has ingredients that were not listed on the label and 1 in 3 were outright fakes.  These results were published in the New York Times then the NY Attorney General Eric Scheniderman's office conducted their own research, which showed even worse results.  Only 21% supplements tested from Wal-Mart, Walgreens, Target, and GNC contained the products listed on the label.  There is massive fraud in the supplement industry.  Overdose of certain supplements may cause toxicity.  Supplements such as omega 3 fish oil might be oxidized therefore causing more toxicity (and anyway raising LDL bad lipoprotein).