(see also Complementary and Alternative Medicine.)
Dietary supplements are the most commonly used of all complementary and alternative therapies, primarily because they are widely available and can be bought without consulting a health care practitioner.
The FDA regulates dietary supplements differently from drugs. The FDA regulates only quality control and good manufacturing processes but does not ensure standardization of the active ingredients or efficacy.
The Dietary Supplement Health Education Act (DSHEA) of 1994 defines a dietary supplement as
In addition, certain hormones, such as dehydroepiandrosterone (DHEA, a precursor to androgens and estrogens) and melatonin, are regulated as dietary supplements and not as prescription drugs.
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 (see the DSHEA legislation at www.fda.gov/RegulatoryInformation/Legislation/default.htm). 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 UTIs).
Safety and efficacy:
Most people who use dietary supplements assume that they are good for health generally, are safe and effective for treating 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, and 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, saw palmetto) 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 at the National Institutes of Health's National Center for Complementary and Alternative Medicine (NCCAM) web site (nccam.nih.gov/research/clinicaltrials).
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), 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 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 different batches produced by the same manufacturer may differ. This product variability is a particular source of difficulty in conducting rigorous scientific 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.
Additional areas of concern include
Most information about these concerns comes from sporadic individual reports (see Table 1: Some Possible Dietary Supplement–Drug Interactions*) and some references.
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 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. 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 NCCAM web site (www.nccam.nih.gov/).
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Last full review/revision May 2009 by Ara DerMarderosian, PhD
Content last modified August 2013