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Known interactions

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What we now about Gan Cao

Scientific Name: Licorice

Other Names: Gan Cao, Glycyrrhiza glabra, Liquorice, Sweet Root

Who is this for?

Note: Note: “True” or “real” licorice may have hormonal or corticoid activity that may affect the body’s ability to regulate blood pressure and mineral balance. However, the candy sold with the name licorice in the United States does not usually contain most of the active chemicals that are found in true licorice. Therefore, consuming American-made licorice candy is not thought to cause many of the effects or side effects of true licorice. In other parts of the world, however, true licorice is included as a flavoring, sweetener, or active ingredient in a wide range of products. Therefore, imported beverages, foods, or pharmaceuticals may contain chemicals that contribute to the medicinal effects of licorice. Consuming licorice-containing products while traveling in countries other than the United States or Canada may also expose individuals to varying amounts of true licorice. Some preparations may be “deglycyrrhized” to remove the suspected harmful chemicals, but the deglycyrrhization process is not always reliable. Due to uncertainty about the actual composition of imported products containing true licorice, consumption of those products should be limited.

About 8% of the licorice plant is made up of a glycoside called glycyrrhizin. Glycosides are chemicals that may have many effects in the body. Glycyrrhizin specifically reduces the activity of two enzymes that break down prostaglandin E (PGE). Low levels of PGE are associated with stomach conditions such as colic, stomach inflammation, and ulcers. By interfering with the body’s removal of PGE, glycyrrhizin allows more PGE to circulate in the blood. The resulting increased levels of PGE may increase the production of stomach mucus and decrease the production of stomach acid. Both effects help to protect stomach tissue, so true licorice has been used to treat ulcers and other stomach conditions.

Glycyrrhizin also encourages the formation of mucus in the respiratory tract. This increase may make respiratory tract mucus less sticky and may also promote its elimination from the body. In addition, very sweet substances such as licorice are known to enhance the elimination of mucus from the lungs. Therefore, true licorice has been used to treat respiratory conditions such as bronchitis. It may also be used to soothe a sore throat. Other chemicals in true licorice are known to suppress coughing, so it may be included in cough syrups and cough lozenges as a cough suppressant, as well as a flavoring.

True licorice also shows some anti-infective and anticancer properties. In laboratory and animal studies, true licorice and chemicals contained in it have stopped or slowed the growth of certain bacteria, fungi, and parasites. Several animal studies have also revealed a possibly strong antiviral effect for true licorice. In these studies, true licorice components that belong to the isoflavonoid class of chemicals appear to have several anti-infective effects that include interference with oxygen utilization by infective micro-organisms. Chemicals derived from true licorice have shown anticancer activity in animal studies and in laboratory cultures of human cancer cells. Additionally, true licorice may have some ability to improve functioning of the immune system. None of these potential effects is well understood and many more studies are needed to confirm or disprove all of them.

True licorice is also thought to have mild influences on sex hormones. It may either increase or decrease natural amounts of the female hormone, estrogen. Animal studies show that high doses of true licorice may prevent estrogen from attaching to estrogen receptors, thereby reducing estrogen’s effects. In other studies, true licorice seemed to speed up the body’s breakdown of estrogen, but only if blood levels of estrogen were already low. If estrogen levels were high, true licorice appeared to have the opposite effect. Taking true licorice may also alter testosterone levels in men. Much more research is needed to understand the possible hormonal effects of true licorice.

For topical use, true licorice or its components may be included in shampoos to reduce scalp oil or in gels to relieve irritated skin. In studies, a gel containing 2% of glycyrrhizin reduced itching, redness, and swelling from dermatitis. Licorice may also be included as a fragrance in products applied to the skin.

When should I be careful taking it?

Early delivery of a baby may be more likely when large amounts (about 5 ounces or more per week) of true licorice are consumed during pregnancy. In addition, taking true licorice may increase the risk of miscarriage due to possible tightening of the uterus. Teas or supplements made from true licorice should not be taken by women who are pregnant.

Water accumulation due to possible corticoid effects from true licorices may worsen congestive heart failure, high blood pressure, kidney disease, liver conditions, or fluid accumulation in the lungs (which may be called pulmonary edema). Individuals with any of these conditions should not take supplemental true licorice.

Although true licorice has not promoted the growth of breast cancer cells under laboratory conditions, women with hormone-dependent conditions such as endometriosis, uterine fibroids, and cancers of the breast, ovaries, or uterus should not take true licorice due to its possible estrogenic effects. Men with prostate cancer should also avoid taking true licorice.

Precautions

Not enough is known about how supplemental true licorice might affect an infant or a small child to recommend its use during breast-feeding or early childhood.

What side effects should I watch for?

Cases of paralysis have been attributed to extremely low potassium levels that were associated with excessive consumption of true licorice.

In at least one study, participants who took 7,000 mg (7 grams) of true licorice per day for 7 days developed a condition known as pseudoaldosteronism. This condition mimics the effects of excessive amounts of the corticoid, aldosterone. Symptoms of pseudoaldosteronism include:

  • Excessive thirst
  • High blood pressure
  • Increased urination
  • Low potassium levels
  • Muscle weakness
  • Weight gain

In men, decreased testosterone levels possibly caused by true licorice may result in a lessened interest in sex and difficulties achieving or maintaining an erection.

Less Severe Side Effects

Single doses of true licorice over 50,000 mg (50 grams or about one and one-half ounces) or smaller daily doses taken continually for longer than 6 weeks may cause:

  • Fatigue
  • Headache
  • Increased blood pressure
  • Muscle spasms
  • Swelling

Cases of allergic reactions to true licorice or one of its components have been reported. Symptoms may include breathing difficulty and rash.

What interactions should I watch for?

Prescription Drugs

True licorice may increase the time blood needs to clot. When it is taken with antiplatelet or anticoagulant drugs, the effect of the drug may be increased, resulting in uncontrolled bleeding.

  • Antiplatelets include Plavix and Ticlid
  • Anticoagulants include heparin and warfarin

When true licorice is taken at the same time as a corticosteroid drug, the effects of both the drug and the supplement may be unpredictable. It is best not to take true licorice and corticosteroids at the same time. Corticosteroids are used to treat a wide range of inflammatory conditions including arthritis, asthma, cancer, eye conditions, and skin infections. Commonly prescribed corticosteroids include:

  • beclomethasone (Beconase, Vancenase)
  • dexamethasone (Decadron)
  • hydrocortisone
  • methylprednisolone (Medrol)
  • prednisolone
  • prednisone (Deltasone)
  • triamcinolone (Azmacort, Nasacort)

Possible potassium deficiency caused by true licorice may increase the risk of side effects from the heart drug, digoxin. Digoxin's side effects may include changes in vision, drowsiness, heart rhythm changes, nausea, and vomiting.

Diuretics ("water pills") such as furosemide and hydrochlorothiazide, may promote the loss of potassium from the body. Since true licorice also may lead to potassium loss, the levels of potassium in the blood may become too low if true licorice is taken at the same time as a water pill. Low blood potassium is called hypokalemia. Symptoms of hypokalemia can include:

  • Abdominal cramps
  • Constipation
  • Muscle weakness
  • Nausea
  • Vomiting
  • Hallucinations
  • Respiratory failure
  • Cardiac arrest

Chemicals in true licorice may act like the female hormone estrogen or they may block the effects of estrogen in the body. When it is taken at the same time as estrogen replacement therapy or oral contraceptives, true licorice may interfere with the way the body uses the estrogen. As a result, estrogens or oral contraceptives may not be as effective, some women may experience increased side effects, and the risk of an unintended pregnancy may be slightly higher.

True licorice may also interfere with testosterone therapy.

Non-prescription Drugs

True licorice may affect the ability of blood to clot after an injury. Aspirin can also delay clotting, so true licorice should not be taken orally at the same time as aspirin.

Some non-prescription laxatives such as Correctol, Dulcolax, and Ex-Lax may promote the loss of potassium from the body. Since true licorice may also increase potassium loss, taking it at the same time as a non-prescription laxative may result in hypokalemia.

Herbal Products

Theoretically, if true licorice is used with other herbs that affect blood clotting, bleeding may occur. Some of the most common herbal products that might inhibit blood clotting are:

  • Danshen
  • Devil's Claw
  • Eleuthero
  • Garlic
  • Ginger (in high amounts)
  • Ginkgo
  • Horse Chestnut
  • Panax Ginseng
  • Papain
  • Red Clover
  • Saw Palmetto

If true licorice is taken with other herbal products, such as motherwort or squill, that have effects on the heart, the chance of side effects may increase. Possible side effects include:

  • Changes in heart rhythm
  • Drowsiness
  • Nausea
  • Vision disturbances
  • Vomiting

When true licorice is taken with other potassium-depleting herbals such as horsetail, the chances of potassium deficiency increase. Low potassium levels may result in symptoms such as drowsiness, heart rhythm changes, nausea, and vision disturbances.

Potassium depletion may also result if true licorice is taken at the same time as herbal laxatives including:

  • Alder Buckthorn
  • Aloe
  • Rhamnus purshiana
  • Rhubarb
  • Senna
  • Yellow dock

Foods

Like true licorice, grapefruit juice may interfere with the body's conversion of cortisol to cortisone. If both are taken together, the risk of high blood pressure and other side effects may be increased.

Some interactions between herbal products and medications can be more severe than others. The best way for you to avoid harmful interactions is to tell your doctor and/or pharmacist what medications you are currently taking, including any over-the-counter products, vitamins, and herbals.

Should I take it?

A bush that grows in warm climates, licorice is thought to have originated in southeastern Europe or southwestern Asia. It was known as both food and medicine to the ancient Greeks, who named it “glyrrhiza”, which means “sweet root”. True licorice has also been used as medicine in China for centuries. Licorice bushes have small leaves and cone-shaped flowers that are blue or purple depending on the species. Most licorice bushes reach about 4 to 5 feet in height when mature and they may live for many years if they are undisturbed. Originally collected from wild plants, most commercial true licorice is now grown on plantations in Mediterranean countries, which produce most of the world’s supply. It is also farmed in China.

To harvest true licorice, the roots of 3 or 4 year old licorice bushes are dug up, dried, and powdered or shredded for use in foods and medicines. Sometimes, the root pieces are toasted before use. In the Middle East, true licorice is used as a sweetening agent; in other parts of the world, it is known more as a flavoring for beverages, foods, and pharmaceuticals. True licorice may also help to preserve substances that break down when exposed to air. The use of true licorice is much more common in Europe and Asia than in the United States. In this country licorice flavoring for foods and medicines is most often provided by anise oil, which is easier and less expensive to obtain. Much of the true licorice that is imported by the United States is used to flavor tobacco for smoking and chewing.

Dosage and Administration

Although suggested doses for true licorice vary widely, a common dose range is 1,000 mg (one gram) to 4,000 mg (4 grams) of powdered true licorice root per day. Capsules and liquid extracts made from powdered true licorice root are the most commonly available single agent forms of true licorice in the United States. Other dosage forms may include chewable tablets and teas. True licorice is often combined with other herbals, such as black cohosh and dong quai, that may have additional estrogenic properties. In addition, true licorice is included in a number of non-prescription products such as cough drops and cough syrups.

Note: Due to the possibility that taking true licorice may cause high blood pressure and other serious side effects, the supplemental use of true licorice (not American-made licorice-flavored candy) in amounts of 2,000 mg (2 grams) per day or greater, should be limited to no more than 4 continuous weeks without a break of at least several days.

Summary

True licorice may be taken by mouth to treat stomach conditions such as ulcers and respiratory conditions such as bronchitis. Topically, true licorice may be anti-infective and anti-inflammatory.

Risks

More than approximately 150,000 mg (150 grams or 5 ounces) of true licorice per week may lead to early birth, if it is taken by a pregnant woman. True licorice may worsen heart, kidney, liver, and lung conditions; it may also affect estrogen-dependent conditions such as breast cancer, endometriosis, and prostate cancer.

Side Effects

Because true licorice blocks the conversion of steroids in the body, consuming large amounts of it may lead to serious side effects such as hypokalemia (low potassium levels) and pseudoaldosteronism. Other side effects from true licorice may include fatigue, headache, and swelling. It also has hormonal properties, which may interfere with the effects of estrogen and decrease the effects of testosterone.

Interactions

True licorice may increase the effects of anticoagulant and antiplatelet drugs and herbals. Taking it may increase the risk of side effects from digoxin, diuretics, grapefruit juice, horsetail, laxatives, and herbal products that have effects on the heart. Because it can act like the hormone, estrogen, in the body, true licorice could interfere with hormone replacement therapy or oral contraceptives.

Last Revised August 6, 2004

References

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Abebe W. An overview of herbal supplement utilization with particular emphasis on possible interactions with dental drugs and oral manifestations. Journal of Dental Hygiene. 2003;77(1):37-46.

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Anon: Licorice. In: DerMarderosian A, Beutler JA, eds. Facts and Comparisons: The Review of Natural Products. St. Louis, MO, Facts and Comparisons. July 1989.

Armanini D, Bonanni G, Palermo M, et al. Reduction of serum testosterone in men by licorice. New England Journal of Medicine. 1999;341:1158.

Armanini D, Fiore C, Mattarello MJ, Bielenberg J, Palermo M. History of the endocrine effects of licorice. Experimental and Clinical Endocrinology in Diabetes. 2002;110(6):257-261.

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(Note: The above information is not intended to replace the advice of your physician, pharmacist, or other healthcare professional. It is not meant to indicate that the use of the product is safe, appropriate, or effective for you.)

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