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In the United States, dietary supplements are defined by the 1994 Dietary Supplement Health and Education Act as products that are not used exclusively as food, but are intended to be consumed in addition to an individual’s diet. The law states that dietary supplements are taken by mouth and contain.

Drug interactions

Dietary supplementDrug
CalciumHeart medicine (e.g., Digoxin) thiazide diuretics (Thiazide, and aluminum- and magnesium-containing antiacids)
MagnesiumThiazide and loop diauretics (e.g., Lasiz®), some cancer drugs (Cisplatin), and magnesium-containing antiacids
Vitamin KBlood thinners (e.g., Coumadin)
St. John’s WortSelective serotonin reuptake inhibitor (SSRI) drugs (antidepressant drugs and birth control pills)

SOURCE: Office of Dietary Supplements, National Institutes of Health, U.S. Department of Health and Human Services.

(Illustration by GGS Information Services/Thomson Gale.)

one or more dietary ingredients. Examples of dietary ingredients include vitamins, minerals, herbs or other biological material, amino acids, and enzymes. Dietary supplements are sold in the form of tablets, capsules, powders, liquids, extracts, or teas. Products sold as dietary supplements are required to be clearly labeled as such.


Dietary supplements serve a wide range of purposes. Some of these are medically appropriate, while others may do nothing or harm the individual. Reasons for taking dietary supplements include:

  • Replacing a necessary substance not found in large enough quantities in the diet
  • Preventing or decreasing the risk of developing a disease or condition
  • Boosting the immune system and improving general health
  • Boosting energy levels
  • Improving mental or physical performance
  • Stimulating weight loss
  • Reducing symptoms of a disease or health condition


Dietary supplements comprise a variety of products ranging from familiar multivitamins found in every supermarket to exotic botanicals such as the South African herb hoodia. Millions of Americans take dietary supplements daily; their use has become increasingly common since the 1990s. The United States Food and Drug Administration (FDA) estimates that in 1999 more than 12 million Americans were taking ephedra, a weight-loss supplement that was later banned because it can cause serious side effects. Due to the large number of different supplements and their range of uses, testing and regulation of these products is difficult and often ineffective.

Dietary supplements and the law

The FDA regulates dietary supplements under the 1994 Dietary Supplement Health and Education Act (DSHEA). At the time the act was passed, legislators believed that because many dietary supplements come from natural sources such as plants and have been used for hundreds of years by practitioners of complementary and alternative medicine (CAM), these products did not need to be as rigorously regulated as prescription and over-the-counter drugs used in conventional medicine.

DSHEA regulates supplements in the same way food is regulated. Like food manufacturers, manufacturers of dietary supplements do not have to prove that a supplement is either safe or effective before it can be sold to the public. Manufacturers of conventional pharmaceutical drugs, however, must prove both safety and effectiveness in humans before a new drug is approved for use. With dietary supplements, the burden of proof falls on the FDA to show that the supplement is either unsafe or ineffective before the supplement can be restricted or banned. Information about a supplement’s safety and effectiveness is normally gathered only after people using the product develop health problems or complain that the product does not work. Initially, supplement manufacturers were not required to report consumer complaints of complications or side effects to the FDA. However, beginning in 2007, a federal law requires all manufacturers of dietary supplements and over-the-counter drugs to report consumer complaints of adverse events (negative side effects) to the FDA. This makes accumulating information on the safety of these products faster and easier.

Dietary supplements are required to be clearly labeled with the word “supplement.” The label must also show the volume or weight of the contents, the serving size, a list of dietary ingredients and non-dietary ingredients (e.g., artificial color, binders, fillers, flavorings), the name of the manufacturer, packer, or distributor, and directions for use. If the supplement is an herb, the label must contain its scientific name.

  • Health claims—Statements indicating a relationship between an ingredient in the supplement and the reduction in the risk of developing a disease or condition. (e.g., Increased intake of folic acid by pregnant women helps reduce the risk of neural tube defects in their offspring.)
  • Nutrient content claims—Statements describing the amount of supplement in the product and may contain words such as “high in,” “good source of,” “fortified,” “enriched,” or “high potency.”
  • Structure or function claims—Description of how the supplement may affect organs or systems in the body without mentioning a specific disease or condition. (e.g., Calcium builds strong bones.) Labels with structure or function claims must also contain the words “This statement has not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.”

Manufacturers of supplements are required to follow federal Good Manufacturing Practices (GMPs) that regulate sanitary and other conditions under which these products are prepared, packaged, and stored. These GMPs are much less stringent than those that regulate the manufacture of conventional drugs. They do not, for example, assure that the amount of active ingredient in each pill or capsule of a dietary supplement is the same. Some supplement manufacturers try to assure consistency of their product by making sure each batch contains the same amounts of active ingredients. This type of standardization is not required by law, and the word “standardized” on the label is not an indication that the product meets any legal requirements as to quality or consistency of contents.

Dietary supplements in conventional medicine

Conventional medicine, also called Western or mainstream medicine, is practiced by licensed medical doctors (MD) and doctors of osteopathy (DO), dentists (DDS or DMD), registered nurses (RN), licensed practical nurses (LPN), pharmacists, and similar health care professionals. Some dietary supplements are routinely used as an accepted part of conventional medicine. The most common of these are vitamin and mineral supplements taken in accordance with established dietary reference intakes (DRIs). DRIs are a set of values for different nutrients that indicate the daily amount of that nutrient necessary to meet the needs of most individuals, as well as the largest amount of the nutrient that can be consumed daily without harmful effects. Other supplements, such as folic acid, are prescribed for pregnant women in order to decrease the risk of neural tube defects in their offspring. Still other supplements, such as enzymes, may be given when the body fails to produce adequate amounts of the enzyme as the result of a genetic disorder such as cystic fibrosis. When taken under supervision of a conventional health care professional, dietary supplements tend to be extremely safe.

Dietary supplements in complementary and alternative medicine

Most dietary supplements are used within a system of complementary and alternative medicine (CAM). Complementary medicine uses treatments that are not part of conventional medicine to supplement conventional medicine. Alternative medicine uses treatments that are not part of conventional medicine as a complete replacement for conventional medicine. Alternative medicine includes well-established treatment systems such as homeopathy, traditional Chinese medicine, and Ayurve-dic, or traditional Indian medicine, as well as newer fad-driven treatments. Many CAM treatments have their roots in tradition and folklore.

Herbs are some of the most common dietary supplements used in CAM. Many have been used for hundreds of years and show evidence of effectiveness. Others are ineffective or may harm the individual either directly or when used as a replacement for conventional drugs and treatments whose effectiveness has been proven. Vitamin and mineral supplements used as part of conventional medicine become part of the CAM system when they are used in mega-doses that far exceed DRI values or when they are used to prevent or treat a specific condition (e.g., vitamin C to prevent colds). Likewise, enzymes and amino acids that have specific uses within conventional medicine become part of the CAM system of dietary supplements when they are used in non-conventional ways or in non-standard doses. Some dietary supplements, such as bee pollen, are used exclusively in CAM.


Individuals interested in using dietary supplements should consult their health care provider and other reputable sources of information before taking any new supplements. Pregnant or breastfeeding women should be especially careful to discuss the supplements they may want to take with their health care provider. Many herbs and other dietary supplements cross the placenta or are secreted into breast milk and may affect the fetus or nursing baby. In addition, care should be taken in giving children dietary supplements. Few studies have been done specifically on children and the recommended dosage for adults may be harmful to children. As with any medication, more is not necessarily better. Overdose is a common cause of adverse side effects in dietary supplements. In the event of side effects, the supplement should be stopped immediately and the side effects reported to a health care professional.


Dietary supplements may interact with both conventional drugs and other herbs or dietary supplements. Individuals should seek information about specific interactions from their health care provider. Many dietary supplements should be stopped several days before surgery to reduce the risk of excess bleeding.


There is strong evidence that some dietary supplements can cause serious harm or death. For example, the weight-loss supplement ephedra was found to have contributed to the death of the Baltimore Oriole’s pitching prospect Steve Belcher in 2003. The FDA later banned ephedra-containing supplements. According to the American Association of Poison Control Centers, there have been over 62,000 reports of vitamin poisonings, over 23,000 cases linked to minerals, and over 23,000 reports linked to herbs. Twenty-seven deaths were attributed to dietary supplements in 2005, of which 13 were attributed to herbs. It should be remembered that “natural” does not mean safe; for example, many wild mushrooms are completely natural and cause death when eaten.

Complications may arise from dietary supplements themselves or their misuse or poor regulation of the manufacturing process. This is especially true of those supplements imported into the United States.


Alternative medicine—A system of healing that rejects conventional, pharmaceutical-based medicine and replaces it with the use of dietary supplements and therapies such as herbs, vitamins, minerals, massage, and cleansing diets. Alternative medicine includes well-established treatment systems such as homeopathy, Traditional Chinese medicine, and Ayurvedic medicine.

Amino acid—Molecules that are the basic building blocks of proteins.

Botanical—An herb; a dietary supplement derived from a plant.

Complementary medicine—Includes many of the same treatments used in alternative medicine, but uses them to supplement conventional drug and therapy treatments, rather than to replace conventional medicine.

Conventional medicine—Mainstream or Western pharmaceutical-based medicine practiced by medical doctors, doctors of osteopathy, and other licensed health care professionals.

Enzyme—Proteins that change the rate of a chemical reaction within the body without themselves being used up in the reaction.

Herb—A plant used in cooking or for medical purposes. Examples include Echinacea and ginseng.

Mineral—An inorganic substance found in the earth that is necessary in small quantities for the body to maintain a health. Examples include zinc, copper, and iron.

Vitamin—A nutrient that the body needs in small amounts to remain healthy but that the body cannot adequately manufacture for itself and must acquire through diet.

from developing countries. Independent laboratory analyses of dietary supplements have found:

  • Contamination with pesticides
  • Contamination with heavy metals
  • Presence of ingredients not listed on the label
  • Amount of dietary ingredient not the same as the amount listed on the label

Parental concerns

Parents should be aware that the RDA and UL for vitamins and minerals are much lower for children than for adults. Accidental overdose may occur if children are give adult vitamins or dietary supplements.


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National Center for Complementary and Alternative Medicine Clearinghouse. P.O. Box 7923, Gathersburg, MD 20898. Telephone: (888) 644-6226. TTY: (866) 464-3615. Fax: (866) 464-3616. Website: <>.

Natural Standard. 245 First Street, 18th Floor, Cambridge, MA 02142. Telephone: (617) 444-8629. Fax: (617) 444-8642. Website: <http://www.naturalstandards>.

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Tish Davidson, A.M.