The two major constituents of licorice are glycyrrhizin and flavonoids. According to test tube studies, glycyrrhizin has anti-inflammatory actions and may inhibit the breakdown of the cortisol produced by the body.66, 67 Licorice may also have antiviral properties, although this has not been proven in human pharmacological studies. Licorice flavonoids, as well as the closely related chalcones, help heal digestive tract cells. They are also potent antioxidants and work to protect liver cells. In test tubes, the flavonoids have been shown to kill Helicobacter pylori, the bacteria that causes most ulcers and stomach inflammation.68 However, it is unclear whether this action applies to the use of oral licorice for the treatment of ulcers in humans.
An extract of licorice, called liquiritin, has been used as a treatment for melasma, a pigmentation disorder of the skin. In a preliminary trial,69 topical application of liquiritin cream twice daily for four weeks led to a 70% improvement, compared to only 20% improvement in the placebo group.
A preliminary trial found that while the acid-blocking drug cimetidine (Tagamet®) led to quicker symptom relief, chewable deglycyrrhizinated licorice (DGL) tablets were just as effective at healing and maintaining the healing of stomach ulcers.70 Chewable DGL may also be helpful in treating ulcers of the duodenum, the first part of the small intestine.71 Capsules of DGL may not work for ulcers, however, as DGL must mix with saliva to be activated.72 One preliminary human trial has found DGL used as a mouthwash was effective in quickening the healing of canker sores.73