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Overview of Dietary Supplements

By

Laura Shane-McWhorter

, PharmD, University of Utah College of Pharmacy

Last full review/revision Jul 2020| Content last modified Jul 2020
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Topic Resources

The US Food and Drug Administration (FDA) regulates dietary supplements differently from drugs. The FDA regulates quality control and good manufacturing processes but does not ensure standardization of the active ingredients or efficacy.

Definition

The Dietary Supplement Health Education Act (DSHEA) of 1994 defines a dietary supplement as

  • Any product (except tobacco)—in pill, capsule, tablet, or liquid form—containing a vitamin, mineral, herb or other plant product, amino acid, or other known dietary substance that is intended as a supplement to the normal diet

Labeling

The DSHEA requires that the product label identify the product as a dietary supplement and notify the consumer that the claims for the supplement have not been evaluated by the FDA. The label must also list each ingredient by name, quantity, and total weight and identify plant parts from which ingredients are derived. Manufacturers are permitted to make claims about the product’s structure and function (eg, good for urinary tract health) but cannot make or imply claims for the product as a drug or therapy (eg, treats urinary tract infections). Expiration dates should also be included on the standardized product labels.

Safety and efficacy

Most people who use dietary supplements assume that they are good for health generally, are safe and effective for treating and/or preventing specific conditions, or both because dietary supplements are natural (ie, derived from plants or animals) and because some are supported by centuries of use in traditional systems of medicine. However, the FDA does not require manufacturers of dietary supplements to prove safety or efficacy (although supplements must have a history of safety). Most supplements have not been rigorously studied. For most, evidence suggesting safety or efficacy comes from

  • Traditional use

  • In vitro studies

  • Certain case reports

  • Animal studies

However, manufacturers and distributors of supplements now must report serious adverse events to the FDA through the MedWatch system. There are a few supplements (eg, fish oil, chondroitin/glucosamine, St. John's wort) now proved to be safe and useful complements to standard drugs.

Evidence concerning the safety and efficacy of dietary supplements is increasing rapidly as more and more clinically based studies are being done. Information about such studies is available from the NIH National Center for Complementary and Integrative Health (NCCIH).

Purity and standardization

Lack of regulation and government monitoring also means that supplements are not monitored to ensure that they contain the ingredients or amount of active ingredient the manufacturer claims they contain. The supplement may have unlisted ingredients, which may be inert or harmful (eg, natural toxins, bacteria, pesticides, lead or other heavy metals, unapproved dyes), or it may contain variable amounts of active ingredients, especially when whole herbs are ground or made into extracts. Consumers are at risk of getting less, more, or, in some cases, none of the active ingredient, if the active ingredient(s) is even known. Most herbal products are mixtures of several substances, and which ingredient is the most active is not always known.

The lack of standardization means not only that products from different manufacturers may vary, but also that separate batches produced by the same manufacturer may differ. This product variability is a particular source of difficulty in conducting rigorous clinical trials and comparing the results among different trials. However, some supplements have been standardized and may include a designation of standardization on the label.

New regulations governing supplement production in the US include rules for Good Manufacturing Practices (GMPs). These rules strengthen standards for keeping manufacturing facilities and equipment clean and raw materials pure and uncontaminated. GMPs also ensure proper labeling, packaging, and storage of the finished product.

Other concerns

Additional areas of concern include

  • Use of dietary supplements instead of conventional drugs

  • Stability of supplements (especially herbal products) once manufactured

  • Toxicity

  • Interactions between supplements and drugs or disease states

  • Contribution to incorrect diagnosis

Despite these concerns, many patients strongly believe in the benefits of supplements and continue to use them with or without a physician’s involvement. Patients may not think to disclose or may wish to conceal their use of dietary supplements. For this reason, the outpatient history should periodically include explicit questions about past and new use of integrative, complementary, and alternative therapies, including dietary supplements. Many physicians incorporate some supplement use into their practice; their reasons include proven benefit of the supplement, a desire to ensure that supplements are used safely by patients who will use supplements anyway, and the physician’s belief that the supplements are safe and effective.

Common concerns about the use of supplements include the following:

  • Placebo effects can simulate true efficacy, particularly if the patient and/or physician strongly believes in the supplement.

  • Therapeutic responses to supplements, placebo-mediated or otherwise, could be mistaken as evidence that confirms a particular, possibly incorrect, diagnosis.

There are few data to guide patient counseling regarding supplement safety. But some experts believe that the overall number of problems due to dietary supplements is rare compared with the overall number of doses taken and that the supplement, if correctly manufactured, is likely to be safe. As a result, these experts advise purchase of supplements from a well-known manufacturer, and many recommend buying supplements made in Germany because there they are regulated as drugs and thus oversight is stricter than in the US.

The following supplements are ones that are most popular, are effective, or have some questions about their safety. More complete information is available through the NIH National Center for Complementary and Integrative Health.

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More Information

The following are some English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

Drugs Mentioned In This Article

Drug Name Select Trade
PARNATE
AFRINOL, SUDAFED
ALDACTONE
OTREXUP
NIZORAL
PREVACID
NEORAL, SANDIMMUNE
ADRENALIN
ERGOMAR
PAXIL
ZOLOFT
INVIRASE
PRILOSEC
CORDARONE
PROZAC, SARAFEM
GLUCOTROL
DILANTIN
LANIAZID
FELDENE
CRIXIVAN
COUMADIN
PANHEPRIN
LANOXIN
No US brand name
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