Antiviral Effects: Since 1980 strong evidence has accumulated supporting the efficacy of several compounds in licorice in the treatment of many types of viral infections. Two recent animal studies have demonstrated that the antiviral effect may be indirect and at least in part may be due to the stimulation of interferon production by T-cells. Glycyrrhizin has been shown in several studies to have antiviral activity against the human immunodeficiency virus (HIV) both in vitro and in vivo. [sic also see 4]

Clinical and laboratory studies carried out mainly in Japan since 1992 have demonstrated the efficacy of glycoside glycyrrhizin in the treatment of viral hepatitis types A, B and C. In summary, recent investigations have demonstrated that several compounds in licorice, primarily glycoside glycyrrhizin, have important antiviral actions. The mechanism of this effect appears to be both a direct inhibitory action on viral replication and function and a stimulating effect on the host immune system to produce interferon, which has known antiviral effects.

Dosage Forms and Recommendations: The German Commission E has approved the use of licorice to treat peptic ulcers and recommends a dosage of 200–600 mg of glycyrrhizin daily. Treatment should not be continued longer than 4–6 weeks because of the known common side effects of licorice use—sodium retention and hypokalemia. Patients with cardiovascular or renal disease should use licorice cautiously and only under the advice and care of a physician. Also, those prone to potassium deficiency should avoid using licorice. A tea can be made by adding approximately 4 g of chopped or freshly grated licorice roots to a cup of hot water. The antiulcer drug carbenoxolone, a licorice derivative, is used extensively in Europe and Japan but is not available in the United States.

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