The United States Pharmacopeia (USP) has a voluntary testing program called the Dietary Supplement Verification Program. The USP Dietary Supplement Verification mark shows that the supplement has passed USP tests to ensure that it contains the ingredients listed on the label, contains the amount of each ingredient listed on the label, dissolves effectively, does not contain harmful contaminants, and was manufactured using safe and sanitary procedures.
Higher costs of particular brands don’t necessarily mean higher quality. Generic brands are often indistinguishable from brand name supplements, but have lower prices. A year’s supply may cost as little as $30.