Herbal supplements have grown into a $19-billion-a-year industry used by 60 million Americans. If you're one of them, how can you find out if your supplement works, or if it's safe?

Under the Dietary Supplement Health and Education Act of 1994, the FDA treats supplements as food. Unlike prescription and over-the-counter drugs, they can make it to market without proving purity, composition, effectiveness, or even safety. And they can stay there until the FDA proves them unsafe after...