The roots of this plant are widely used, not only in European herbal medicine but also in the traditional Chinese pharmacopoeia.
In China and parts of Russia, the species used is G. uralensis; it is known in Chinese as gan cao. The scientific name for the genus refers to the sweet taste of the root.
Licorice has been popular for flavoring foods and other medicinal herbs for many centuries. Hippocrates described its medicinal use, as did Pliny the Elder.
A piece of licorice from the eighth century was recently discovered still to contain active principles.
Licorice has been used to treat coughs and colds, and also as a digestive aid.
Although licorice is best known in the United States as a flavor for candy, by far the majority (up to 90 percent) of the licorice imported into the country is actually used to flavor tobacco products.
Just to add to the confusion, some of the licorice candy made in the United States does not rely on licorice for its flavor.
A recent case of licorice overdose, however, demonstrated that the popular candy Twizzlers (the black, not the red) contains some licorice, and natural candies imported from Europe often contain licorice rather than anise or other flavoring agents.
The parts of the plant used are the dried roots and rhizomes, either peeled or unpeeled.
Between 6 and 14 percent of the root is the glycoside glycyrrhizin. This calcium or potassium salt of glycyrrhizinic acid is fifty times sweeter than table sugar.
Licorice contains a number of other triterpenoid saponins, along with plant sterols including sitosterol and stigmasterol.
The root also contains several other sugars, including glucose, mannose, and sucrose.
More than thirty flavonoids and isoflavonoids have been identified, including liquiritin and its derivatives.
Some coumarins and an immunosuppressant called LX have also been isolated.
In Europe, the primary medicinal use of licorice is to treat coughs, colds, and other respiratory infections.
Glycyrrhizinic acid seems to stop the growth of many bacteria and of viruses such as influenza A. It also stimulates the production of interferon.
Chinese researchers agree that licorice is effective against cough and soothes the inflamed tissues of a sore throat. In fact, ancient Chinese texts summarize the uses of licorice rather well: “improve the tone of the ‘middle Jiao’ [digestive system] and replenish qi, to remove ‘heat’ and toxic substance, to moisturize the lungs and arrest coughing, and to relieve spasms and pain.”
Modern practitioners use different terminology, but the therapeutic benefits are quite similar.
Licorice has also been used extensively as a treatment for ulcers. It prevents the secretion of gastric acid, reduces the activity of pepsin, and inhibits enzymes that dismantle prostaglandins. This leads to higher levels of prostaglandins in the stomach and upper intestine, allowing ulcers to heal more quickly.
The activity of licorice on prostaglandin-regulating enzymes may explain why this herb protects stomach tissue against aspirin-induced damage in rat studies.
A semisynthetic compound (carbenoxolone) derived from licorice has been compared to cimetidine in clinical trials and found less effective (52 percent improving compared to 78 percent on cimetidine). This agent does act to protect the colon, however, and is used to treat ulcerative colitis in China. Carbenoxolone also protects against colon cancer.
Serious side effects that occur with licorice and with carbenoxolone led researchers to develop a deglycyrrhizinated licorice, DGL. In some studies, DGL (under the brand name Caved-S) was just as good as cimetidine at treating ulcers, but not all studies have shown consistently good results.
In Japan, physicians use licorice to treat chronic hepatitis B. Glycyrrhizin interferes with hepatitis B surface antigen and is synergistic with interferon against hepatitis A virus. It is also used at times to treat hepatitis C.
Researchers have also demonstrated that licorice helps protect the liver from damage due to chemotherapy. At low doses, the herb stimulates the liver to manufacture cholesterol and excrete it in bile. This can help lower serum cholesterol levels.
Licorice root has an effect on the organism similar to that of a steroid. It slows the conversion of cortisol to cortisone, which increases and prolongs the action of this steroid hormone produced by the adrenal glands. This physiological activity can explain many of its undesirable effects as well as its medicinal benefits.
In Russia, however, this property is put to use by administering licorice together with prescribed cortisone. This allows for a lower dose of the medication.
Physicians in China may prescribe licorice alone or with cortisol to treat mild cases of Addison’s disease, in which the body produces too little of this hormone.
Glycyrrhizin also inhibits an enzyme that inactivates aldosterone, and its chronic use can mimic the serious condition of aldosteronism.
In China, licorice is considered a powerful antitoxin and is used as an aid in the treatment of pesticide poisoning.
It may also curb Plasmodium falciparum, the parasite that causes malaria.
Through its effects on adrenal steroids, licorice exerts anti-inflammatory activity.
The licorice constituent known as LX immunosuppressant is also able to reduce hypersensitivity reactions and prolong the survival time of transplanted tissues.
Glycyrrhizin has antioxidant and antitumor activity, but because of serious side effects it should not be used on a regular basis.
Licorice has been used to ease symptoms of menopause. In one study, licorice attached to estrogen receptors. It did not, however, promote the growth of uterine cells as estrogen does, and it is not frequently used for this purpose in the United States.
Topically, glycyrrhizin has been used in shampoo to treat excess oil secretion of the scalp. It has also been included in ointments used to treat skin inflammations.
For coughs and colds: approximately 5 g per day (approximately 1 teaspoons licorice root made into tea).
For ulcers and stomach problems: up to 15 g per day.
In China, gan cao extract is given in doses of 5 to 15 ml three times a day.
DGL: 380 to 760 mg twenty minutes before each meal (three times daily).
Licorice should not be used for long-term self-treatment. At low doses, four to six weeks should be the maximum duration. At higher doses, as for treating ulcers, the time frame is correspondingly shorter.
As little as one ounce (approximately 30 g) of natural licorice candy daily may be enough to trigger side effects over a period of weeks or months.
Regular daily intake of 50 g licorice root (corresponding to 100 mg glycyrrhizin) is known to trigger high blood pressure and other problems (see **Adverse Effects**).
Pregnant women should not use licorice at medicinal doses. There is a danger of high blood pressure or of a hormone imbalance that would harm the fetus.
People with high blood pressure should avoid the use of licorice, which could aggravate their condition.
Anyone with a heart problem should use licorice only under medical supervision. Potassium depletion caused by licorice is especially hazardous for such patients. Anyone with pre-existing hypokalemia (low potassium) should not take licorice.
People with kidney disease, especially the elderly, may be at increased risk of side effects from this herb.
Gallbladder disease and cirrhosis are considered contraindications for licorice.
The consequences of high doses or long-term use of licorice are severe. This herb can cause high blood pressure, low levels of potassium, fluid retention and swelling of the face and limbs, hormonal imbalance, and muscle destruction leading to pain and weakness.
At least one woman experienced loss of libido. Another woman ate too much licorice candy and lost a great deal of potassium; her heart stopped.
Licorice can also change heart rhythms, prolonging QT and PR intervals on an electrocardiogram.
Lethargy and fatigue as well as weakness are part of the picture of licorice toxicity.
Many of the negative symptoms associated with licorice are due to its ability to inhibit the renin-angiotensin system. Elderly people in particular are susceptible to kidney problems as a consequence of licorice.
Paralysis of the legs (and in one case, of all of the limbs) has been reported. A sixty-four-year-old man developed pulmonary edema, signaled by fatigue and trouble breathing, after eating four packages of black Twizzlers licorice candy in three days. This case demonstrates how quickly a serious reaction can arise.
Licorice can reduce thyroid gland activity and lower the basal metabolic rate.
It appears that individuals vary considerably in their susceptibility to adverse reactions from licorice. Some people experience negative symptoms within days, while others may ingest excessive licorice in candy, chewing gum, chewing tobacco, or herbal medicine for months or even years before they realize that they are suffering damaging effects.
Women appear to be somewhat more susceptible than men, and oral contraceptives may increase this sensitivity.
Licorice can greatly increase potassium loss due to medicines such as hydrochlorothiazide, Lasix, Hygroton, Lozol, Bumex, and other potassium-wasting diuretics.
Severe potassium loss greatly increases the risk of heart rhythm irregularities, especially in people taking Lanoxin. Amiloride, a potassium-sparing diuretic, is not recommended to counteract the potassium loss caused by licorice.
Because it binds to serum albumin, licorice may interact with other medications that bind to serum albumin as well: ibuprofen, aspirin, and Coumadin. The coumarins in licorice may also potentiate the action of this anticoagulant, possibly leading to unexpected bleeding.
Because of its impact on the thyroid gland, licorice may alter the required dose of levothyroxine (Synthroid, Levothroid, Levoxyl). Likewise, its impact on cortisol may alter the effectiveness and appropriate dose of cortisonelike drugs.
Aldactone (spironolactone) is likely to be affected by the action of licorice on aldosterone. Oral contraceptives may make women more vulnerable to hypertension, potassium loss, fluid retention, and other adverse effects of licorice.