Overview of Medicinal Herbs and Nutraceuticals: Medicinal Herbs and Nutraceuticals: Merck Manual Home Edition

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	Medicinal Herbs and Nutraceuticals
		Overview of Medicinal Herbs and Nutraceuticals
			Safety and Effectiveness
			Purity and Standardization
			Interactions With Drugs

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Overview of Medicinal Herbs and Nutraceuticals

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Medicinal herbs are plant parts, sometimes ground, extracted, or otherwise prepared, used for health benefits. Nutraceuticals, a more recent and more general term, are 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): Overview of Complementary and Alternative Medicine), 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 and 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, and 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), can have unwanted side effects.

Safety and Effectiveness

Because dietary supplements are not regulated as drugs by the FDA, their manufacturers are not required to prove that supplements are safe and effective (although they must have a history of safety). Consequently, few supplements have been studied rigorously 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 been recognized only recently, much of the available information has not been gathered systematically or scientifically and so is difficult to evaluate. In contrast, both prescription and nonprescription (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: Drug 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 clear, reliable answers. For some supplements, the only evidence suggesting effectiveness is 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 contain other substances, including, in some cases, prescription or nonprescription drugs and even dangerous substances such as mercury.

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 contains 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 subject to standardization can be difficult. Some supplements, particularly those produced in Europe, 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.

Although the content of a supplement is not standardized, the way in which it is manufactured has been standardized. In 2007, the FDA created current good manufacturing practices (GMPs) that standardize the manufacturing, packaging, labeling, and storing of dietary supplements. These GMPs help ensure the quality of dietary supplements and help protect the public health.

Interactions With Drugs

Supplements can interact with prescription and nonprescription 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.

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Some Possible Medicinal Herb–Drug Interactions
Medicinal Herb	Affected Drugs	Interaction
Chamomile	Anticoagulants (drugs that prevent blood clots, such as warfarinSome Trade Names COUMADIN )	Chamomile taken with anticoagulants may increase the risk of bleeding.
	Sedatives (such as barbiturates and benzodiazepines)	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, amiodaroneSome Trade Names CORDARONE , methotrexateSome Trade Names TREXALL , and ketoconazoleSome Trade Names NIZORAL )	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.
Echinacea	Immunosuppressants (drugs that intentionally suppress the immune system, such as corticosteroids and cyclosporineSome Trade Names NEORAL SANDIMMUNE )	By stimulating the immune system, echinacea may negate the effects of immunosuppressants.
Ephedra*	Stimulant drugs (such as caffeine, epinephrine, phenylpropanolamine, and pseudoephedrineSome Trade Names AFRINOL SUDAFED )	Ephedra contains ephedrine, which is a stimulant that increases the stimulant effects of other drugs, increasing the risk of irregular or rapid heart rate and high blood pressure.
Ephedra*	Monoamine oxidase inhibitors (MAOIs, a type of antidepressant)	Ephedrine may intensify the effects of these drugs and increase the risk of side effects, such as headache, tremors, irregular or rapid heart rate, and high blood pressure.
Feverfew	Anticoagulants (such as warfarinSome Trade Names COUMADIN )	Feverfew taken with anticoagulants may increase the risk of bleeding.
	Iron	Feverfew may reduce iron absorption.
	Drugs used to manage migraine headaches (such as ergotamineSome Trade Names ERGOMAR )	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 warfarinSome Trade Names COUMADIN )	Garlic taken with anticoagulants may increase the risk of bleeding.
	Drugs that decrease blood sugar levels (hypoglycemic drugs, such as insulinSome Trade Names HUMULIN NOVOLIN and glipizideSome Trade Names GLUCOTROL )	Garlic may intensify the effects of these drugs, causing an excessive decrease in blood sugar levels (hypoglycemia).
	Protease inhibitors (such as indinavirSome Trade Names CRIXIVAN or saquinavirSome Trade Names INVIRASE ), which are used to treat human immunodeficiency virus (HIV) infection	Garlic decreases blood levels of protease inhibitors, making them less effective.
Ginger	Anticoagulants (such as warfarinSome Trade Names COUMADIN )	Ginger taken with anticoagulants may increase the risk of bleeding.
Ginkgo	Anticoagulants (such as warfarinSome Trade Names COUMADIN ), aspirinSome Trade Names BAYER , and other NSAIDs	Ginkgo taken with anticoagulants or with aspirinSome Trade Names BAYER or other NSAIDs may increase the risk of bleeding.
	Anticonvulsants (such as phenytoinSome Trade Names DILANTIN )	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 warfarinSome Trade Names COUMADIN ), aspirinSome Trade Names BAYER , and other NSAIDs	Ginseng taken with anticoagulants or with aspirinSome Trade Names BAYER 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.
	DigoxinSome Trade Names LANOXIN	Ginseng may increase digoxinSome Trade Names LANOXIN levels.
	Estrogen 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 warfarinSome Trade Names COUMADIN )	Goldenseal may oppose the effects of anticoagulants and may increase the risk of blood clots.
Green tea	WarfarinSome Trade Names COUMADIN	Green tea may cause warfarinSome Trade Names COUMADIN to be less effective.
Kava	Sedatives (such as barbiturates and benzodiazepines)	Kava may intensify or prolong the effects of sedatives.
Licorice (glycyrriza glabra)^†	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.
	DigoxinSome Trade Names LANOXIN	Because licorice increases urine formation, it can result in low levels of potassium, which is excreted in urine. When licorice is taken with digoxinSome Trade Names LANOXIN , the low potassium levels increase the risk of digoxinSome Trade Names LANOXIN 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 spironolactoneSome Trade Names ALDACTONE , 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.
Milk thistle	Protease inhibitors (such as indinavirSome Trade Names CRIXIVAN or saquinavirSome Trade Names INVIRASE ), which are used to treat HIV infection	Milk thistle decreases blood levels of protease inhibitors, making them less effective.
Saw palmetto	Estrogen 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 the risk of side effects such as drowsiness.
	CyclosporineSome Trade Names NEORAL SANDIMMUNE	St. John's wort may reduce blood levels of cyclosporineSome Trade Names NEORAL SANDIMMUNE , making it less effective, with potentially dangerous results (such as rejection of an organ transplant).
	DigoxinSome Trade Names LANOXIN	St. John's wort may reduce blood levels of digoxinSome Trade Names LANOXIN , making it less effective, with potentially dangerous results.
	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.
	Nonnucleoside reverse transcriptase inhibitors	St. John's wort increases the metabolism of these drugs, reducing their effectiveness.
	Oral contraceptives	St. John's wort increases the metabolism of these drugs, reducing their effectiveness.
	Photosensitizing drugs (such as lansoprazoleSome Trade Names PREVACID , omeprazoleSome Trade Names PRILOSEC , piroxicamSome Trade Names FELDENE , and sulfonamide antibiotics)	When taken with these drugs, St. John's wort may increase the risk of sun sensitivity.
	Protease inhibitors (such as indinavirSome Trade Names CRIXIVAN or saquinavirSome Trade Names INVIRASE ), which are used to treat HIV infection	St. John's wort may reduce blood levels of protease inhibitors, making them less effective.
	Selective serotonin reuptake inhibitors (such as fluoxetineSome Trade Names PROZAC , paroxetineSome Trade Names PAXIL , and sertralineSome Trade Names ZOLOFT )	St. John's wort may intensify the effects of these drugs.
	WarfarinSome Trade Names COUMADIN	St. John's wort may reduce blood levels of warfarinSome Trade Names COUMADIN , making it less effective and clot formation more likely.
Valerian	Anesthetics	Valerian may prolong sedation time.
Valerian	Sedatives (such as barbiturates and benzodiazepines)	Valerian may intensify or prolong the effects of sedatives, causing excessive sedation.
*Sale of supplements containing ephedra is banned in the United States.
^†True, natural licorice, not the more common, artificially flavored licorice candy.

Some Possible Medicinal Herb–Drug Interactions

Medicinal Herb

Affected Drugs

Interaction

Chamomile	Anticoagulants (drugs that prevent blood clots, such as warfarinSome Trade Names COUMADIN )	Chamomile taken with anticoagulants may increase the risk of bleeding.
	Sedatives (such as barbiturates and benzodiazepines)	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, amiodaroneSome Trade Names CORDARONE , methotrexateSome Trade Names TREXALL , and ketoconazoleSome Trade Names NIZORAL )	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.
Echinacea	Immunosuppressants (drugs that intentionally suppress the immune system, such as corticosteroids and cyclosporineSome Trade Names NEORAL SANDIMMUNE )	By stimulating the immune system, echinacea may negate the effects of immunosuppressants.
Ephedra*	Stimulant drugs (such as caffeine, epinephrine, phenylpropanolamine, and pseudoephedrineSome Trade Names AFRINOL SUDAFED )	Ephedra contains ephedrine, which is a stimulant that increases the stimulant effects of other drugs, increasing the risk of irregular or rapid heart rate and high blood pressure.
Ephedra*	Monoamine oxidase inhibitors (MAOIs, a type of antidepressant)	Ephedrine may intensify the effects of these drugs and increase the risk of side effects, such as headache, tremors, irregular or rapid heart rate, and high blood pressure.
Feverfew	Anticoagulants (such as warfarinSome Trade Names COUMADIN )	Feverfew taken with anticoagulants may increase the risk of bleeding.
	Iron	Feverfew may reduce iron absorption.
	Drugs used to manage migraine headaches (such as ergotamineSome Trade Names ERGOMAR )	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 warfarinSome Trade Names COUMADIN )	Garlic taken with anticoagulants may increase the risk of bleeding.
	Drugs that decrease blood sugar levels (hypoglycemic drugs, such as insulinSome Trade Names HUMULIN NOVOLIN and glipizideSome Trade Names GLUCOTROL )	Garlic may intensify the effects of these drugs, causing an excessive decrease in blood sugar levels (hypoglycemia).
	Protease inhibitors (such as indinavirSome Trade Names CRIXIVAN or saquinavirSome Trade Names INVIRASE ), which are used to treat human immunodeficiency virus (HIV) infection	Garlic decreases blood levels of protease inhibitors, making them less effective.
Ginger	Anticoagulants (such as warfarinSome Trade Names COUMADIN )	Ginger taken with anticoagulants may increase the risk of bleeding.
Ginkgo	Anticoagulants (such as warfarinSome Trade Names COUMADIN ), aspirinSome Trade Names BAYER , and other NSAIDs	Ginkgo taken with anticoagulants or with aspirinSome Trade Names BAYER or other NSAIDs may increase the risk of bleeding.
	Anticonvulsants (such as phenytoinSome Trade Names DILANTIN )	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 warfarinSome Trade Names COUMADIN ), aspirinSome Trade Names BAYER , and other NSAIDs	Ginseng taken with anticoagulants or with aspirinSome Trade Names BAYER 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.
	DigoxinSome Trade Names LANOXIN	Ginseng may increase digoxinSome Trade Names LANOXIN levels.
	Estrogen 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 warfarinSome Trade Names COUMADIN )	Goldenseal may oppose the effects of anticoagulants and may increase the risk of blood clots.
Green tea	WarfarinSome Trade Names COUMADIN	Green tea may cause warfarinSome Trade Names COUMADIN to be less effective.
Kava	Sedatives (such as barbiturates and benzodiazepines)	Kava may intensify or prolong the effects of sedatives.
Licorice (glycyrriza glabra)^†	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.
	DigoxinSome Trade Names LANOXIN	Because licorice increases urine formation, it can result in low levels of potassium, which is excreted in urine. When licorice is taken with digoxinSome Trade Names LANOXIN , the low potassium levels increase the risk of digoxinSome Trade Names LANOXIN 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 spironolactoneSome Trade Names ALDACTONE , 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.
Milk thistle	Protease inhibitors (such as indinavirSome Trade Names CRIXIVAN or saquinavirSome Trade Names INVIRASE ), which are used to treat HIV infection	Milk thistle decreases blood levels of protease inhibitors, making them less effective.
Saw palmetto	Estrogen 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 the risk of side effects such as drowsiness.
	CyclosporineSome Trade Names NEORAL SANDIMMUNE	St. John's wort may reduce blood levels of cyclosporineSome Trade Names NEORAL SANDIMMUNE , making it less effective, with potentially dangerous results (such as rejection of an organ transplant).
	DigoxinSome Trade Names LANOXIN	St. John's wort may reduce blood levels of digoxinSome Trade Names LANOXIN , making it less effective, with potentially dangerous results.
	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.
	Nonnucleoside reverse transcriptase inhibitors	St. John's wort increases the metabolism of these drugs, reducing their effectiveness.
	Oral contraceptives	St. John's wort increases the metabolism of these drugs, reducing their effectiveness.
	Photosensitizing drugs (such as lansoprazoleSome Trade Names PREVACID , omeprazoleSome Trade Names PRILOSEC , piroxicamSome Trade Names FELDENE , and sulfonamide antibiotics)	When taken with these drugs, St. John's wort may increase the risk of sun sensitivity.
	Protease inhibitors (such as indinavirSome Trade Names CRIXIVAN or saquinavirSome Trade Names INVIRASE ), which are used to treat HIV infection	St. John's wort may reduce blood levels of protease inhibitors, making them less effective.
	Selective serotonin reuptake inhibitors (such as fluoxetineSome Trade Names PROZAC , paroxetineSome Trade Names PAXIL , and sertralineSome Trade Names ZOLOFT )	St. John's wort may intensify the effects of these drugs.
	WarfarinSome Trade Names COUMADIN	St. John's wort may reduce blood levels of warfarinSome Trade Names COUMADIN , making it less effective and clot formation more likely.
Valerian	Anesthetics	Valerian may prolong sedation time.
Valerian	Sedatives (such as barbiturates and benzodiazepines)	Valerian may intensify or prolong the effects of sedatives, causing excessive sedation.
*Sale of supplements containing ephedra is banned in the United States.
^†True, natural licorice, not the more common, artificially flavored licorice candy.

Last full review/revision February 2009 by Ara DerMarderosian, PhD

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