On January 8th, 2008, the FDA updated a warning letter issued on December 22nd, 2008 about weight loss products that are marketed to consumers that contain controlled substances or prescription medications that are not declared on the ingredients list.
You can see the warning here.
Unfortunately quality and purity standards are lacking in the nutritional supplement industry and this case highlights the importance of using reliable supplement manufacturers that test raw material, test finished products and have integrity. While this issues with this list of dietary supplements is egregiously bad, similar issues exist with many supplements you buy over the counter or even get from you natural health practitioner.