Dietary supplements were defined in a law passed by Congress in 1994 called the Dietary Supplement Health and Education Act (DSHEA). According to DSHEA, a dietary supplement is a product that:
- Is intended to supplement the diet
- Contains one or more dietary ingredients (including vitamins, minerals, herbs or other botanicals, amino acids, and certain other substances) or their constituents
- Is intended to be taken by mouth, in forms such as tablet, capsule, powder, softgel, gelcap, or liquid
- Is labeled as being a dietary supplement.
Herbal supplements are one type of dietary supplement. An herb is a plant or plant part (such as leaves, flowers, or seeds) that is used for its flavor, scent, and/or potential health-related properties. “Botanical” is often used as a synonym for “herb.” An herbal supplement may contain a single herb or mixtures of herbs. The law requires that all of the herbs be listed on the product label.
Research has shown that some uses of dietary supplements are beneficial to health. For example, scientists have found that folic acid (a vitamin) prevents certain birth defects. Other research on dietary supplements has failed to show benefit; for example, several major studies of the herbal supplement echinacea did not find evidence of benefit against the common cold.