Ods.od.nih.gov contains scores of fact sheets from the federal Office of Dietary Supplements on individual vitamins, minerals, and other dietary supplements.
Fda.gov/food/dietarysupplements provides FDA warnings about products that consumers may be taking. The FDA site also provides general tips regarding the consumption of dietary supplements.
Consumerlab.com is an independent research firm that, for a $30 annual fee, allows a subscriber to access the results of tests it runs to verify the quality and effectiveness of supplements.
Usp.org/uspverified is the home page of the U.S. Pharmacopeia, which has set standards for medicines for 200 years. The site provides a listing of products that have “earned the USP Verified Mark.”