Dietary supplements is a general term that refers to vitamins, minerals, herbs or other plants, amino acids (the individual building blocks of protein), or parts of these substances. They can be in pill, capsule, tablet, or liquid form. They supplement (add to) the diet and should not be considered a substitute for food.
Common dietary supplements include vitamins and minerals (such as vitamin C or a multivitamin), botanicals (herbs and plant products), and substances that come from a natural source (such as omega-3 fatty acids). Sometimes these supplements are the basis for some of today’s common medicines. For example, people have used willow bark tea for centuries to relieve fever. Pharmaceutical companies eventually identified the chemical in willow bark that relieved fever and used that knowledge to produce aspirin.
The U.S. Food and Drug Administration (FDA) does not regulate dietary supplements in the same way that it regulates medicine. A dietary supplement can be sold without research on how well it works.
* Source: University of Michigan Dietary Supplements (Herbal Medicine and Natural Products) overview.