Most of us think of licorice as that product in the candy aisle that looks like a package of pencil-thin, twisted rope. Available in black and red varieties, individuals tend to either really like or dislike licorice’s distinct flavor. Although the type of licorice available in a typical American candy shop is only flavored as licorice, it would no doubt surprise many candy connoisseurs to know that true licorice is not so much a man-made confection as an ancient plant-based compound with a very definite coloring and flavor. Licorice, or Glycyrrhiza glabra, is an ancient herb with documented uses in Chinese and Ayurvedic medicine.1

Background

Medically, licorice traditionally has been used as a general anti-inflammatory, antitussive, GI soothant, and for respiratory support.2 The potential for antiviral activity and hepatocellular protection in cases of hepatitis C has also been discussed.

Glycyrrhizin is the ingredient in licorice responsible for most of its medicinal properties. The main concern with pure licorice is the potential for this compound to interact negatively with medications or become toxic in large quantities. Many licorice products labeled DGL (deglycyrrhized licorice) are being studied to determine whether removing this ingredient makes the product ineffective or if the remaining isoflavones, coumarins, and flavinoids are also medicinally active.3

Science

Early documented use of licorice compounds most commonly concerns GI distress. Healing of peptic ulcers, gastritis, and heartburn are common in folk and medical literature. In a randomized, placebo-controlled trial, 120 patients with “functional dyspepsia” were given either placebo or an herbal mixture containing a significant percentage of DGL extract. A standardized symptom score completed by the participants assessed gastric symptoms. At the end of the eight-week trial, the treatment group showed a 43% reduction in symptoms over the placebo group. Since the licorice was mixed with other herbs, however, this trial was inconclusive.4

A more recent trial designed to explore licorice’s anti-inflammatory potential examined the effect of a glycyrrhizin compound on human neutrophils. The results confirmed definite prostaglandin and cyclo-oxygenase inhibition even in the absence of significant amounts of glycyrrhizin.5 Given the intense emphasis on the development of anti-inflammatory medications that are safe for the GI system, a harmless herbal product with efficacy would be a tremendous discovery.

A Japanese laboratory study found licorice extract to have in vitro inhibitory action against the growth of Helicobacter pylori, known to play a major role in the development of duodenal ulcers. The licorice compound remained effective even when the H. pylori strain was amoxicillin- and clarithromycin-resistant.6

As a source of support for the respiratory system, licorice has also been a favorite of natural medicine for centuries. Recent studies, however, have verified these properties and even expanded the findings when examining the compound’s potential in treating asthma.

In an intriguing trial, patients with diagnosed bronchial asthma were given either licorice compound or placebo for four weeks. Plasma leukotriene and nitric oxide levels were measured, as was pulmonary function. A statistically significant improvement in pulmonary function and a decrease in the inflammatory mediators were demonstrated.7 These actions, combined with the expectorant and antispasmodic action of licorice, make it a worthy consideration in asthma management.

The treatment of hepatitis C is the latest focus of licorice research. Although trials have not shown licorice compounds to be effective at reducing viral loads, evidence showing a reduction in the incidence of hepatitis C-related carcinoma and fibrosis has been documented.8 A Japanese study showed a favorable response to licorice therapy among more than 1,000 hepatitis C patients who were poor responders to interferon therapy. After 13 years of follow-up, the treatment group’s rate of hepatocellular carcinoma was less than half that of the control group.9

Safety, interactions

Licorice compounds—even the DGL form—have been show to have extensive interactions with such medications as oral contraceptives, nonsteroidal anti-inflammatory drugs, thiazide diuretics, potassium chloride, corticosteroids, and blood thinners.3

Long-term or large-quantity ingestion of licorice in its natural form can lead to serious cardiovascular and adrenal side effects, including hypokalemia, hypertension, and adrenal imbalance similar to Cushing’s syndrome.3

Dose, how supplied

Doses no larger than 100 mg/day are advised for chronic use, regardless of the formulation. In addition to a confection or flavoring extract, licorice is available as a tonic, tea, or capsule.10

Summary

The potential benefits of licorice seem exciting. However, in light of the severity of potential side effects and toxicities and the lengthy list of medication interactions, licorice should not be on the list of supplements that health-care providers recommend for their patients.

References

1. Memorial Sloan-Kettering Cancer Center. Licorice.
2. University of Maryland Medical Center. Licorice. 

3. Fetrow CW, Avila JR. Professional’s Handbook of Complementary & Alternative Medicines. Springhouse, Pa.: Springhouse Corp.; 1999:393.

4. Madisch A, Holtmann G, Mayr G, et al. Treatment of functional dyspepsia with a herbal preparation. A double-blind, randomized, placebo-controlled, multicenter trial. Digestion. 2004;69:45-52.

5. Chandrasekaran CV, Deepak HB, Thiyagarajan P, et al. Dual inhibitory effect of Glycyrrhiza glabra (GutGard) on COX and LOX products. Phytomedicine. 2011;18:278-284.

6. Fukai T, Marumo A, Kaitou K, et al. Anti-Helicobacter pylori flavonoids from licorice extract. Life Sci. 2002;71:1449-1463.

7. Houssen ME, Ragab A, Mesbah A, et al. Natural anti-inflammatory products and leukotriene inhibitors as complementary therapy for bronchial asthma. Clin Biochem. 2010;43:887-890.

8. Kumada H. Long-term treatment of chronic hepatitis C with glycyrrhizin [stronger neo-minophagen C (SNMC)] for preventing liver cirrhosis and hepatocellular carcinoma. Oncology. 2002;62 Suppl 1:94-100.

9. Veldt BJ, Hansen BE, Ikeda K, et al. Long-term clinical outcome and effect of glycyrrhizin in 1093 chronic hepatitis C patients with non-response or relapse to interferon. Scand J Gastroenterol. 2006;41:1087-1094.

10. Natural Medicines Comprehensive Database. Licorice.

All electronic documents accessed March 15, 2011