Here's what the Food and Drug Administration just said about so-called dietary supplements and foods claimed to promote weight loss:
If you find yourself making this common New Year’s resolution, know this: many so-called “miracle” weight loss supplements and foods (including teas and coffees) don’t live up to their claims. Worse, they can cause serious harm, say FDA regulators. The agency has found hundreds of products that are marketed as dietary supplements but actually contain hidden active ingredients (components that make a medicine effective against a specific illness) contained in prescription drugs, unsafe ingredients that were in drugs that have been removed from the market, or compounds that have not been adequately studied in humans.
If you want detailed information on the topic, the FDA has webpage for you.