Medicinal herbs generally refer to plant parts, sometimes ground, extracted, or otherwise prepared, used for health benefits. Nutraceuticals, a more recent and more general term, refer to a group of natural substances that includes certain herbs and such products as cholesterol-lowering margarines and psyllium-fortified products that are used as dietary supplements and regulated as foods.

Traditional systems of medicine have been used throughout the world for centuries. Certain ancient systems, such as traditional Chinese medicine, Ayurveda (the holistic system of medicine from India), and Tibetan medicine, are still used extensively, particularly in their country of origin. In the United States, interest in the therapies of such systems, particularly for the treatment of chronic illness, is growing. These therapies, usually referred to as complementary or alternative medicine (see Complementary and Alternative Medicine (CAM): Introduction), range from medicinal herbs to acupuncture to massage. Most of them have not been studied scientifically, and nearly all are unregulated.

The most commonly used alternative therapy is dietary supplements, which include medicinal herbs and nutraceuticals. Because the use of dietary supplements is widespread, the United States government passed the Dietary Supplement Health Education Act (DSHEA) in 1994. It defines a dietary supplement as any product (besides tobacco) that contains a vitamin, mineral, herb, or amino acid and that is intended as a supplement to the normal diet. The act requires that the label of a dietary supplement identify it as such. The label must state that the claims for the dietary supplement have not been evaluated by the Food and Drug Administration (FDA). The label must also list each ingredient by name, quantity, and total weight and must identify the plant parts from which each ingredient is derived.

Most dietary supplements used in alternative medicine are derived from plants; some are derived from animals. Because such dietary supplements are natural, some people assume that they are safe to use. However, a substance is not necessarily safe just because it is natural. For example, many potent poisons, such as hemlock, are derived from plants, and some, such as snake venoms, are derived from animals. Furthermore, almost all substances that affect the body—whether dietary supplements or drugs approved for medical use by the FDA (see Overview of Drugs: Prescription or Nonprescription) have both wanted and unwanted effects (side effects).

Safety and Effectiveness: Because dietary supplements are not regulated as drugs by the FDA, their manufacturers are not required to prove that dietary supplements are safe and effective (although they must have a history of safety). Consequently, few supplements have been rigorously studied for safety and effectiveness (although some may eventually be shown to be safe and effective). Furthermore, because the need to evaluate supplements in humans has only recently been recognized, much of the available information has not been gathered systematically or scientifically and so is difficult to evaluate. In contrast, both prescription and over-the-counter drugs have been extensively and systematically studied by researchers and reviewed for safety and effectiveness by the FDA (see Overview of Drugs: Effectiveness and Safety). These studies include those in animals to detect the development of cancer and organ damage and those in humans to detect any signs of toxicity.

The amount and quality of evidence supporting the effectiveness of supplements varies greatly. For some supplements, evidence supporting their effectiveness is convincing. However, for most, scientific studies have not been designed well enough to provide the desired information. For some supplements, the only evidence suggesting effectiveness are reports about individual people or studies conducted in animals.

Purity and Standardization: Other areas of concern are the purity and standardization of supplements. Supplements, unlike drugs, are not regulated to ensure that they are pure or that they contain the ingredients or the amount of active ingredient they claim to contain. As a result, the supplement may not be pure. Or, the amount of active ingredient in a dose of a supplement may vary, especially when whole herbs are ground or made into extracts to produce a tablet, capsule, or solution. The buyer is at risk of getting less, more, or, in some cases, none of the active ingredient in a supplement. Standardization requires that each individual dosage form of the product contain a precise amount of its active ingredient or ingredients. However, most herbal products are mixtures of several substances, and which ingredient is the most active is not always known. Therefore, determining which ingredient or ingredients should be considered active and thus would be subject to standardization can be difficult. Some supplements have been standardized and may include a designation of standardization on the label.

Advice on how to choose a pure, standardized product varies from expert to expert. Most experts recommend buying from a well-known manufacturer, and many recommend buying products made in Germany, because oversight of supplements is stricter there than in the United States.

Interactions With Drugs: Supplements can interact with prescription and over-the-counter drugs. Such interactions may intensify or reduce the effectiveness of a drug or cause a serious side effect. Before taking supplements, people should consult their doctor, so that such interactions can be avoided. Few well-designed studies have been conducted to investigate supplement-drug interactions, so most information about these interactions comes from sporadic individual reports of interactions.

Some Possible Medicinal Herb—Drug Interactions Medicinal Herb Affected Drugs Interaction Chamomile Anticoagulants (such as warfarin) Chamomile taken with anticoagulants may increase the risk of bleeding   Barbiturates (such as phenobarbital) and other sedatives Chamomile may intensify or prolong the effects of sedatives   Iron Chamomile may reduce iron absorption Echinacea Drugs that can damage the liver (such as anabolic steroids, amiodarone, methotrexate, and ketoconazole) Echinacea taken for more than 8 weeks may damage the liver. When echinacea is taken with another drug that can damage the liver, the risk of liver damage may be increased   Immunosuppressants (such as corticosteroids and cyclosporine) By stimulating the immune system, echinacea may negate the effects of immunosuppressants Feverfew Anticoagulants (such as warfarin) Feverfew taken with anticoagulants may increase the risk of bleeding   Iron Feverfew may reduce iron absorption   Drugs used to manage migraine headaches (such as ergotamine) Feverfew may increase heart rate and blood pressure when it is taken with drugs used to manage migraine headaches   Nonsteroidal anti-inflammatory drugs (NSAIDs) NSAIDs reduce the effectiveness of feverfew in preventing and managing migraine headaches Garlic Anticoagulants (such as warfarin) Garlic taken with anticoagulants may increase the risk of bleeding   Drugs that decrease blood sugar levels (hypoglycemic drugs, such as insulin and glipizide) Garlic may intensify the effects of these drugs, causing an excessive decrease in blood sugar levels (hypoglycemia)   Saquinavir (used to treat HIV infection) Garlic decreases blood levels of saquinavir, making it less effective Ginger Anticoagulants (such as warfarin) Ginger taken with anticoagulants may increase the risk of bleeding Ginkgo Anticoagulants (such as warfarin), aspirin and other NSAIDs Ginkgo taken with anticoagulants or with aspirin or other NSAIDs may increase the risk of bleeding   Anticonvulsants (such as phenytoin) Ginkgo may reduce the effectiveness of anticonvulsants in preventing seizures   Monoamine oxidase inhibitors (MAOIs, a type of antidepressant) Ginkgo may intensify the effects of these drugs and increase the risk of side effects, such as headache, tremors, and manic episodes Ginseng Anticoagulants (such as warfarin), aspirin and other NSAIDs Ginseng taken with anticoagulants or with aspirin or other NSAIDs may increase the risk of bleeding   Drugs that decrease blood sugar levels (hypoglycemic drugs) Ginseng may intensify the effects of these drugs, causing an excessive decrease in blood sugar levels (hypoglycemia)   Corticosteroids Ginseng may intensify the side effects of corticosteroids   Digoxin Ginseng may increase digoxin levels   Estrogen replacement therapy Ginseng may intensify the side effects of estrogen   MAOIs Ginseng can cause headache, tremors, and manic episodes when it is taken with MAOIs   Opioids (narcotics) Ginseng may reduce the effectiveness of opioids Goldenseal Anticoagulants (such as warfarin) Goldenseal may oppose the effects of anticoagulants and may increase the risk of blood clots Licorice Antihypertensives Licorice may increase salt and water retention and increase blood pressure, making antihypertensives less effective   Antiarrhythmics Licorice may increase the risk of an abnormal heart rhythm, making antiarrhythmic therapy less effective   Digoxin Because licorice increases urine formation, it can result in low levels of potassium, which is excreted in urine. When licorice is taken with digoxin, the low potassium levels increase the risk of digoxin toxicity   Diuretics Licorice may intensify the effects of most diuretics, causing increased, rapid loss of potassium. Licorice may interfere with the effectiveness of potassium-sparing diuretics, such as spironolactone, making these diuretics less effective   MAOIs Licorice may intensify the effects of these drugs and increase the risk of side effects, such as headache, tremors, and manic episodes Milk thistle Drugs that decrease blood sugar levels (hypoglycemic drugs) Milk thistle may intensify the effects of these drugs, causing an excessive decrease in blood sugar levels   Saquinavir Milk thistle decreases blood levels of saquinavir, making it less effective Saw palmetto Estrogen replacement therapy and oral contraceptives Saw palmetto may intensify the effects of these drugs St. John's wort Benzodiazepines St. John's wort may reduce the effectiveness of these drugs in reducing anxiety and may increase drowsiness and the risk of side effects such as drowsiness   Cyclosporine St. John's wort may reduce blood levels of cyclosporine, making it less effective, with potentially dangerous results (such as rejection of an organ transplant)   Digoxin St. John's wort may reduce blood levels of digoxin, making it less effective, with potentially dangerous results   Indinavir (a drug used to treat AIDS) St. John's wort may reduce blood levels of indinavir, making it less effective   Iron St. John's wort may reduce iron absorption   MAOIs St. John's wort may intensify the effects of MAOIs, possibly causing very high blood pressure that requires emergency treatment   Photosensitizing drugs (such as lansoprazole, omeprazole, piroxicam, and sulfonamide antibiotics) When taken with these drugs, St. John's wort may increase the risk of sun sensitivity   Selective serotonin reuptake inhibitors (such as fluoxetine, paroxetine, and sertraline) St. John's wort may intensify the effects of these drugs   Warfarin St. John's wort may reduce blood levels of warfarin, making it less effective and clot formation more likely Valerian Anesthetics Valerian may prolong sedation time   Barbiturates Valerian may intensify the effects of barbiturates, causing excessive sedation

Last full review/revision February 2003