Added this text (note reference to a NEJM article documenting these problems):
To cite only one example, in 2011, a large "well respected" Utah supplement company marketed a product, Zotrex supposedly containing an natural herb, Ophioglossum polyphyllous, it claimed could enhance potency. What the pills actually contained was sulfoaildenafil, a drug analog of Viagra that has never been tested in humans. Quite a few drug analogs of safe drugs, are toxic for humans, for example, phenformin, which is a close relative to the very safe, well-tested drug metformin.
In another case, a supposedly "herbal" diabetes supplement, when taken to the lab turned out to contain a cheap first generation sulfonyurea drug--one that can cause dangerous hypos and, which is also now known to act on the heart in a way that promotes heart attack.
The 1994 law stipulated that supplement makers were supposed to submit safty data to the FDA for any new ingredient they introduced that wasn't on sale prior to 1994. But the New England Journal of Medicine reported in January of 2012 (HERE) that since 1994,
..the number of available dietary supplements has skyrocketed from an estimated 4000 to more than 55,000...but the FDA has received adequate notification for only 170 new supplement ingredients since 1994 — undoubtedly a small fraction of the ingredients for which safety data should have been submitted.
Any time there is any attempt to reintroduce even the feeblest oversight into the marketing of bottles that can contain literally anything, the supplement companies send paid minions out who post all over the web about how big gumint's trying to take away your freedom. People deluge their congresspeople with complaints, and the supplement companies go back to earning billions selling you whatever they feel like putting into their magic pills this month.
Also removed paragraph about vitamins being manufactured in China.