http://www.ftc.gov/bcp/conline/pubs/buspubs/dietsupp.htm
This guide was written by the FTC for the dietary supplement industry and is meant to ensure that advertising for dietary supplements is truthful and not misleading. The Guide -- actually a restatement of long-standing FTC policies -- is divided into three main sections. The first two sections explain how the FTC identifies the claims conveyed by an ad and how it evaluates the adequacy of the substantiation for those claims. The third section covers consumer testimonials, expert endorsements, and advertising claims based on historical or traditional use of supplements.