Dietary supplements: what do you need to know about them?

The Dietary Supplement Health and Safety Act (DSHEA) of 1994 defines a dietary supplement as any product (except tobacco) - in the form of a pill, capsule, tablet, or liquid - containing a vitamin, mineral, herb, amino acid, or other recognized dietary substance that is intended to be a supplement to the normal diet.

The act requires that the product label identify the product as a dietary supplement and notify the consumer that the supplement's claims have not been evaluated by the Food and Drug Administration; the label must also list each ingredient by name, amount, and total weight and identify the parts of the plant from which the ingredients are derived (see DSHEA at www.fda.gov ). Manufacturers are allowed to provide information about the product's composition and function (e.g., benefits for healthy urinary tract function), but are not allowed to make or imply claims that the product can be used as a drug or therapeutic agent (e.g., treats urinary tract infections).

Dietary supplements are the most commonly used of all complementary and alternative therapies, primarily because they are widely available and can be purchased without consulting a health professional. Most patients who use dietary supplements believe that they are beneficial for overall health, safe and effective for treating specific conditions, or all of these properties, and that the supplements are believed to be natural (i.e., derived from plants or animals) and some have been used in traditional medicine for centuries. However, the FDA treats dietary supplements differently than drugs. The FDA only regulates quality control and manufacturing processes, but does not ensure standardization of active ingredients. However, some steps are being taken, albeit slowly. Also, the FDA does not require manufacturers of dietary supplements to provide certification of safety or effectiveness (although supplements must have a reputation for safety). Most supplements have not been rigorously studied. For most, evidence of safety or effectiveness comes from tradition of use, laboratory studies, and some anecdotal reports and animal studies. However, some supplements (e.g., fish oil, chondroitin/glucosamine, saw palmetto) have been shown to be safe and useful complements to standard medications. The body of evidence for the safety and effectiveness of dietary supplements is growing rapidly as more and more clinical studies are conducted. Information about such studies can be found on the National Institutes of Health National Center for Complementary and Alternative Medicine (NCCAM) website ( www.nccam.nih.gov ).

Lack of regulation and government monitoring also means that supplements are not tested to ensure that they contain the same ingredients or the same amount of active ingredient that the supplement manufacturer claims. A supplement may contain unlisted ingredients that may be inert or harmful, or may contain varying amounts of active ingredients, especially depending on whether the herbal powders or extracts are used. Consumers risk getting less, more, or in some cases no active ingredient, even if the active ingredient is known. Most herbal supplements are mixtures of several substances, and it is not always known which ingredient is the most active. Some supplements have been standardized and may have evidence of standardization on the label.

Additional concerns include the use of dietary supplements in place of real drugs, the stability of supplements (especially herbal preparations) that have been manufactured for some time, the toxicity of supplements in children and the elderly, and interactions between supplements and drugs. Most of the information about such issues comes from sporadic individual reports of interactions between supplements and drugs and a few cases.

Despite these problems with supplements, many patients still have blind faith in the usefulness of supplements and continue to use them with or without a physician's recommendation. Patients may not admit to taking supplements or may wish to conceal the fact that they are using dietary supplements. For this reason, the outpatient history should periodically include direct questions about the patient's past and present use of complementary and alternative therapies, including dietary supplements. Many physicians include the use of some supplements in their practice; reasons for doing so may include the proven usefulness of the supplement, a desire to ensure that the supplement is used safely by patients who will use the supplements anyway, and the physician's belief that the supplements are safe and effective. There is limited evidence to make informed recommendations about safe supplement use, but some experts believe that the overall number of problems associated with dietary supplements is small compared with the total number of doses taken and that a well-made product is probably safe. As a result, experts advise buying supplements from reputable manufacturers, often recommending that you give preference to supplements made in Germany, where they are considered drugs and thus subject to stricter controls than in the United States.

Some possible effects of interactions between dietary supplements and drugs

Dietary supplements	Medicines affected by the additive	Interaction
Chamomile	Barbiturates and other sedatives	It may enhance or prolong the effect of sedatives because its volatile oils have additive effects.
	Iron supplements	May reduce iron absorption through plant tannins
	Warfarin	May increase the risk of bleeding because chamomile contains phytocoumarins, which may have additive effects.
Echinacea	Drugs metabolized by cytochrome P450 enzymes (eg, amiodarone, anabolic steroids, ketoconazole, methotrexate)	When taken together, these drugs may increase the risk of hepatotoxicity by slowing their metabolism.
	Immunosuppressants (eg, corticosteroids, cyclosporine)	May reduce immunosuppressive effects through T cell stimulation
Pyrethrum	Anti-migraine medications (eg, ergotamine, methysergide)	May increase heart rate and blood pressure because they have additive vasoconstrictive effects; may enhance the effects of methysergide
	Antiplatelet medications	May increase the risk of bleeding because feverfew inhibits platelet aggregation (has additive effects)
	Iron supplements	May reduce iron absorption through plant tannins
	Nonsteroidal anti-inflammatory drugs	The effectiveness of feverfew in preventing and relieving migraine headaches is reduced by nonsteroidal anti-inflammatory drugs.
	Warfarin	May increase the risk of bleeding because warfarin may have additive effects
Garlic	Antihypertensive drugs	May increase the antihypertensive effect
	Antiplatelet medications	May increase the risk of bleeding because these drugs negate garlic's inhibition of platelet aggregation and fibrinolytic effects
	Protease inhibitors (eg, saquinavir)	Garlic Lowers Blood Levels of Protease Inhibitors
	Warfarin	May increase the risk of bleeding by enhancing the effects of the anticoagulant warfarin.
Ginkgo	Anticonvulsants (eg, phenytoin)	May reduce the effectiveness of anticonvulsants, as impurities in ginkgo formulations may reduce the effects of the anticonvulsant
	Aspirin and other nonsteroidal anti-inflammatory drugs	May increase the risk of bleeding by enhancing inhibition of antiplatelet aggregation
	Warfarin	May increase the risk of bleeding by enhancing the effects of the anticoagulant warfarin
Ginseng	Antihypoglycemic drugs (eg, glipizide)	May enhance the effects of these medications, causing hypoglycemia
	Aspirin and other nonsteroidal anti-inflammatory drugs	May increase the risk of bleeding by enhancing inhibition of antiplatelet aggregation
	Corticosteroids	May enhance adverse effects of corticosteroids as ginseng has anti-inflammatory effects
	Estrogens	May increase digoxin levels May increase adverse effects of estrogen
	Monoamine oxidase inhibitors (eg, tranylcypromine)	May cause headaches, concussions and fits of madness
	Warfarin	May increase the risk of bleeding by enhancing the anticoagulant effects of warfarin
Hydrastis	Warfarin and Heparin	May counteract the effects of warfarin and heparin, increasing the risk of thromboembolism
Maryin thistle	Antihypoglycemic drugs	May enhance the effects of these medications, causing hypoglycemia
	Indinavir	May interfere with the function of assimilation enzymes, lowering the level of indinavir in the blood
Saw Palmetto	Estrogens (eg, oral contraceptives)	May increase the effects of these medications
St. John's Wort	Cyclosporine	May reduce blood levels of cyclosporine, increasing the risk of rejection in organ transplants May reduce blood levels of digoxin, making it less effective, with potentially dangerous results
	Iron supplements	May reduce iron absorption
	Monoamine oxidase inhibitors	May increase the effects of monoamine oxidase inhibitors, causing very high blood pressure that may require emergency treatment.
	Irreversible transcriptase inhibitors	Increases the metabolism of these drugs, reducing their effectiveness
	Oral contraceptives	Increases the metabolism of these drugs, reducing their effectiveness
Ginger	Antiplatelet medications	May increase the risk of bleeding by increasing inhibition of platelet aggregation
	Warfarin	May increase the risk of bleeding by enhancing the effects of the anticoagulant warfarin.
Valerian	Barbiturates	May enhance the effects of barbiturates, causing excessive sedation

When dietary supplements are used, special care is required because these products are not standardized and therefore vary widely, and because information on their use is continually changing. The theoretical status of much of the interaction material does not eliminate the need for cautious use. Before prescribing any drug, health care practitioners should ask patients whether they are taking dietary supplements and, if so, which ones. Practitioners should identify any potential adverse drug-supplement interactions the patient is taking and then determine the appropriate drugs and dosages.

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