National Institutes of Health • National Center for Complementary and Alternative Medicine
Safe Use of Dietary Supplements: What the Science Says
What the Science Says
Although many dietary supplements (and some prescription drugs) come from natural sources, “natural” does not always mean “safe.” For example, the herbs comfrey and kava can cause serious harm to the liver. Also, a manufacturer’s use of the term “standardized” (or “verified” or “certified”) does not necessarily guarantee product quality or consistency.
Be aware that an herbal supplement may contain dozens of compounds and that its active ingredients may not be known. Researchers are studying many of these products in an effort to identify active ingredients and understand their effects in the body. Also consider the possibility that what’s on the label may not be what’s in the bottle. Analyses of dietary supplements sometimes find differences between labeled and actual ingredients. For example:
- An herbal supplement may not contain the correct plant species.
- The amount of the active ingredient may be lower or higher than the label states. That means you may be taking less—or more—of the dietary supplement than you realize.
- The dietary supplement may be contaminated with other herbs, pesticides, or metals, or even adulterated with unlabeled ingredients such as prescription drugs.
For current information from the Federal Government on the safety of particular dietary supplements, check the “Dietary Supplement and Safety Information” section of the FDA Web site or the “Alerts and Advisories” section of the NCCAM Web site.
Federal Regulation of Dietary Supplements
The Federal Government regulates dietary supplements through the U.S. Food and Drug Administration (FDA). The regulations for dietary supplements are not the same as those for prescription or over-the-counter drugs. In general, the regulations for dietary supplements are less strict.
- A manufacturer does not have to prove the safety and effectiveness of a dietary supplement before it is marketed. A manufacturer is permitted to say that a dietary supplement addresses a nutrient deficiency, supports health, or is linked to a particular body function (e.g., immunity), if there is research to support the claim. Such a claim must be followed by the words “This statement has not been evaluated by the U.S. Food and Drug Administration (FDA). This product is not intended to diagnose, treat, cure, or prevent any disease.”
- Manufacturers are expected to follow certain “good manufacturing practices” (GMPs) to ensure that dietary supplements are processed consistently and meet quality standards. Requirements for GMPs went into effect in 2008 for large manufacturers and are being phased in for small manufacturers through 2010.
- Once a dietary supplement is on the market, the FDA monitors safety. If it finds a product to be unsafe, it can take action against the manufacturer and/or distributor, and may issue a warning or require that the product be removed from the marketplace.
Also, once a dietary supplement is on the market, the FDA monitors product information, such as label claims and package inserts. The Federal Trade Commission (FTC) is responsible for regulating product advertising; it requires that all information be truthful and not misleading.
The Federal Government has taken legal action against a number of dietary supplement promoters or Web sites that promote or sell dietary supplements because they have made false or deceptive statements about their products or because marketed products have proven to be unsafe.
Sources of Science-Based Information for Dietary Supplements
It’s important to look for reliable sources of information on dietary supplements so you can evaluate the claims that are made about them. The most reliable information on dietary supplements is based on the results of rigorous scientific testing. For more information visit PubMed, a database of the National Library of Medicine that provides an easy way to access millions of journal citations.
NCCAM has a central role in addressing the need for reliable, objective information on complementary products and practices based on scientific evidence so that both consumers and health care providers can make well-informed decisions. Although a lot of information about complementary health approaches, including dietary supplements, is available in the public domain, much of it is incomplete, misleading, inaccurate, or based on scientifically unproven claims. In addition, much of the public’s use of complementary health products and practices occurs without the guidance from health care providers. This reinforces the need for reliable, objective, evidence-based information regarding the usefulness and safety—or lack thereof—of these health approaches.
If your patients are considering using a dietary supplement, NCCAM has resources that can help you discuss safety and ensure coordinated care.
Talking With Your Patients About the Safety of Dietary Supplements
- Encourage your patients to take charge of their health by being informed consumers. Find out what the scientific evidence says the safety of a dietary supplement and whether it works.
- Keep in mind that “natural” does not necessarily mean “safe.”
- Some dietary supplements may interact with medications (prescription or over-the-counter) or other dietary supplements, and some may have side effects on their own.
- Encourage your patients to tell you about any complementary health products or practices they use, including dietary supplements. This will help give you a full picture of what they are doing to manage their health and will help ensure coordinated and safe care. (For tips about talking with your patients about complementary health products and practices, see NCCAM’s Time to Talk campaign.) It is especially important for your patients to talk with you if they are:
- Thinking about replacing regular medications with one or more dietary supplements.
- Taking any medications (whether prescription or over-the-counter), as some dietary supplements have been found to interact with medications.
- Planning to have surgery. Certain dietary supplements may increase the risk of bleeding or affect the response to anesthesia.
- Pregnant or nursing a baby, or are considering giving a child a dietary supplement. Most dietary supplements have not been tested in pregnant women, nursing mothers, or children.
NCCAM Clinical Digest is a service of the National Center for Complementary and Alternative Medicine, NIH, DHHS. NCCAM Clinical Digest, a monthly e-newsletter, offers evidence-based information on CAM, including scientific literature searches, summaries of NCCAM-funded research, fact sheets for patients, and more.
The National Center for Complementary and Alternative Medicine is dedicated to exploring complementary and alternative healing practices in the context of rigorous science, training CAM researchers, and disseminating authoritative information to the public and professionals. For additional information, call NCCAM's Clearinghouse toll-free at 1-888-644-6226, or visit the NCCAM Web site at nccam.nih.gov. NCCAM is 1 of 27 institutes and centers at the National Institutes of Health, the Federal focal point for medical research in the United States.
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