The federal Food and Drug Administration does not analyze the content of dietary supplements, which do not need proof of safety or effectiveness before they go on sale. Here are tips from the government on their use:

- Don't self-diagnose a health condition or substitute a supplement for medicine.

- Ask your doctor before taking a supplement, especially if you are pregnant, taking other medicines or are having surgery soon.

- Request proof from the manufacturer or distributor to back up any claims.

- Ask the seller or manufacturer for information on tests showing safety or effectiveness of ingredients, and whether consumers have complained of adverse events.

- Look for "seals of approval" from independent groups that have standards to help ensure the product was properly made, contains what the label says, and is free of contaminants. These groups include Consumerlab.com, NSF and the U.S. Pharmacopeia.

- Web resources:

Tips from FDA: http://www.cfsan.fda.gov/.875DMS/ds-savvy.html

ConsumerLab.com quality seal: http://www.consumerlab.com/seal.asp

NSF certification: http://tinyurl.com/d3e3k7

U.S. Pharmacopeia verification program: http://www.usp.org/USPVerified/dietarySupplements/