There are a number of great online resources for learning more about dietary supplements.
MATTHEW T. STALLBAUMER
Before adding a dietary supplement to your health routine, research the ingredients or speak to your doctor to avoid possible drug/herb interactions and complications. For example, St. John's wort, a popular treatment for depression, can negate the effectiveness of oral contraceptives as well as protease inhibitors used to treat HIV. Here are several online resources to get you started. Also read What You Should Know About Drugs vs. Herbs
Herbs for Health magazine
Memorial Sloan-Kettering Cancer Center
American Botanical Council
Center for Food Safety and Applied Nutrition
National Center for Complementary and Alternative Medicine