Dietary Supplements


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 one or more dietary ingredients. Examples of dietary ingredients include vitamins, minerals, herbs or other biological materials, 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 provide no benefit and may even harm the individual. Reasons for taking dietary supplements include:

Tips to avoid drug interactions

SOURCE: “Avoiding Drug Interactions.” (accessed April 22, 2018).


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 National Center for Health Statistics reported that in 2006, 53% of all adult Americans were taking at least one dietary supplement. This was an increase from 42% using dietary supplements in the mid-1990s. However, between 2006 and 2011, the percentage of users has remained fairly constant at just over half the adult population.

Dietary supplements and the law

Due to the large number of different supplements and their range of uses, testing and regulation of these products is difficult and often ineffective. The U.S. Food and Drug Administration (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 tested and regulated as prescription and over-the-counter drugs used in conventional medicine.

Drug interactions

Dietary supplement



Heart medicine (e.g., Digoxin), thiazide diuretics (Thiazide, aluminum- and magnesium-containing antacids)

Ginkgo biloba

Anticonvulsant drugs (Tegretol, Equetro, Carbatrol, Depakote)


Blood thinners (Coumadin, heparin, aspirin, ibuprofen, naproxen, ketoprofen), monoamine oxidase inhibitors (MAOIs)


Thiazide and loop diuretics (e.g., Lasiz®), some cancer drugs (Cisplatin), magnesium-containing antacids

St. John's wort

Selective serotonin reuptake inhibitor (SSRI) drugs, heart drug Lanoxin, cholesterol-lowering drugs Mevacor and Altocor, Viagra

Vitamins E and K

Blood thinners (e.g., Coumadin)

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

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, such as artificial color, binders, fillers, and 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.

Unlike conventional drugs, the label for a dietary supplement does not have to provide statements about possible side effects. However, dietary supplements are not legally allowed to claim they can “cure,” “treat,” “mitigate,” “prevent,” or “diagnose” a specific disease. They may make the following claims:

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, ensure that the amount of active ingredient in each pill or capsule of a dietary supplement is the same. Some supplement manufacturers try to ensure 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), doctors of osteopathy (DO), dentists (DDS or DMD), registered nurses (RN), licensed practical nurses (LPN), pharmacists, and similar healthcare 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 healthcare professional, dietary supplements tend to be extremely safe.

Dietary supplements in complementary and alternative medicine

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 megadoses that far exceed DRI values or when they are used to prevent or treat a specific condition, such as 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 unconventional ways or in nonstandard doses. Some dietary supplements, such as bee pollen, are used exclusively in CAM.


It is difficult to determine whether dietary supplements are safe or effective because of the loose way that they are regulated. Many of the studies done on supplements are poorly designed, have a small sample size, or are sponsored by the manufacturer of the supplement, making the results questionable. Natural Standard is an independent organization that evaluates studies, scientific evidence, and expert opinion on CAM treatments and therapies and makes impartial judgments concerning their safety and effectiveness. The National Center for Complementary and Alternative Medicine is a government organization within the National Institutes of Health that investigates CAM treatments and runs rigorous clinical trials to determine safety and effectiveness.

Individuals interested in using dietary supplements should consult their healthcare 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 healthcare 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 healthcare professional.

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 (TCM), and Ayurvedic medicine.
Amino acid—
Molecules that are the basic building blocks of proteins.
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 healthcare professionals.
Proteins that change the rate of a chemical reaction within the body without themselves being used up in the reaction.
A plant used in cooking or for medical purposes. Examples include echinacea and ginseng.
An inorganic substance found in the earth that is necessary in small quantities for the body to maintain health. Examples include zinc, copper, and iron.
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.



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 Orioles pitching prospect Steve Belcher in 2003. The FDA later banned ephedra-containing supplements. According to the American Association of Poison Control Centers, in 2009 there were more than 64,000 reports of adult vitamin poisonings. There were also over 19,000 cases in children under age five of poisoning by dietary supplements, herbal medicines, or homeopathic remedies; two children died. 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, their misuse, or poor regulation of the manufacturing process. This is especially true of those supplements imported into the United States from developing countries. Independent laboratory analyses of dietary supplements have found:

Some health professionals believe the number of complications related to dietary supplements is severely underreported.

Parental concerns

Parents should be aware that the recommended dietary allowances (RDAs) and tolerable upper intake levels (ULs) for vitamins and minerals are much lower for children than for adults. Accidental overdose may occur if children are given adult vitamins or dietary supplements.

See also Açaí berry ; Antioxidants ; Biotin ; Calcium ; Carotenoids ; Choline ; DHEA ; Dietary reference intakes (DRIs) ; Echinacea ; Ephedra ; Ergogenic aids ; Flaxseed ; Folate ; Ginkgo biloba ; Ginseng ; Glucosamine ; Green tea ; Hoodia ; Iron ; Macronutrients ; Magnesium ; Minerals ; Omega-3 and omega-6 fatty acids ; Prebiotics and probiotics ; Turmeric ; Vitamin C ; Vitamin D ; Vitamin E ; Vitamin K ; Vitamins .




Bonakdar, Robert A. The H.E.R.B.A.L. Guide: Dietary Supplement Resources for the Clinician. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2010.

PDR staff. PDR for Nonprescription Drugs, Dietary Supplements, and Herbs. 31st ed. Montvale, NJ: PDR Network, 2010.


MedlinePlus. “Dietary Supplements.” U.S. National Library of Medicine, National Institutes of Health. (accessed March 25, 2018).

MedlinePlus. “Herbal Medicine.” U.S. National Library of Medicine, National Institutes of Health. (accessed March 25, 2018).

National Center for Complementary and Integrative Health (NCCIH). “Dietary and Herbal Supplements.” National Institutes of Health. (accessed March 25, 2018).

Office of Dietary Supplements. “Dietary Supplements: Background Information.” National Institutes of Health. (accessed March 25, 2018).

Office of Inspector General, U.S. Department of Health and Human Services. Dietary Supplements: Structure/Function Claims Fail to Meet Federal Requirements, OEI-01-11-00210.October 2, 2012. (accessed March 25, 2018).


American Botanical Council, PO Box 144345, Austin, TX, 78714, (512) 926-4900, (800) 373-7105, Fax: (512) 926-2345,, .

Council for Responsible Nutrition, 1828 L St. NW, Ste. 510, Washington, DC, 20036, (202) 204-7700, Fax: (202) 204-7701,, . .

Natural Standard, One Davis Sq., Somerville, MA, 02144, (617) 591-3300, Fax: (617) 591-3399,, .

Office of Dietary Supplements, National Institutes of Health, 6100 Executive Blvd., Rm. 3B01, MSC 7517, Bethesda, MD, 20892-7517, (301) 435-2920, Fax: (301) 480-1845,, .

Tish Davidson, A.M.

  This information is not a tool for self-diagnosis or a substitute for professional care.