Licorice is the common name for the Glycyrrhiza genus of plants that includes over 30 species including Glycyrrhiza Glabra. Licorice grows native to the Mediterranean area, Central Russia, Asia and parts of the Middle East. Licorice root has a characteristic sweet taste and is used commercially as a sweetener. The chemical composition of licorice includes saponins, flavonoids, isoflavones, coumarins and stilbenoids. Glycyrrhizin (glycyrrhizic or glycyrrhizinic acid) is the main triterpenoid saponin present in licorice root, gives licorice its characteristic sweet taste. Glycyrrhizin is 50 times as sweet as sugar, which it explains its colloquial name of sweet root. Glycyrrhizin is metabolised to glycyrrhetinic acid by intestinal bacteria in humans through the activity of β-D-glucuronidase, and is then absorbed. Flavonoids give licorice the characteristic yellow colour and include flavonols and chalcones. Licorice contains a number of other minor constituents including fatty acids, phenols, γ-lactones, glucose, sucrose, starch and polysaccharides.
Licorice has been used as a medicinal herb from as far back as 500 BC. In this regard it is used as a traditional remedy for peptic ulcer disease, hepatitis C, constipation, cough, blood sugar disorders, skin diseases, and as a laxative. Because of its widespread use as a traditional medicine the pharmacological actions of the herb have been investigated using cell culture, animal and human studies. One of the most researched effects of licorice is the antiinflammatory action is possesses. This is possibly due to the β-glycyrrhetinic acid in the herb which may inhibit glucocorticoid metabolism, thus potentiating the effects of glucocorticoids. Alternatively, β-glycyrrhetinic may inhibit the classical complement pathway activation. Licorice is also effective at preventing oxidative stress, and this may in turn reduce tissue inflammation. However, although β-glycyrrhetinic has been extensively investigated for its antiinflammatory activity, other components of the herb may contribute to the antiinflammatory effects of licorice.
Licorice also possesses antimicrobial activity and is able to inhibit the growth of several kinds of bacteria including methicillin-resistant Staphylococcus aureus and Escherichia coli. The antimicrobial effects on helicobacter pylori explain the ability of licorice to prevent and treat peptic ulcers. Replication of viruses may also be inhibited by constituents of licorice through induction of apoptosis in virus infected cells. Licorice also possesses antiprotozoal effects and has been shown to inhibit the growth of plasmodium falciparum and leishmania donovani, the organisms responsible for falciparum malaria and leishmaniasis, respectively. Some of the disease inhibiting effects of licorice may stem from its ability to inhibit oxidative stress, which is likely the result of the polyphenolic compounds within the herb. The isoflavonoid glabridin may accumulate in immune cells and inhibit oxidative stress by increasing cellular glutathione levels. In addition glabridin can bind to low density lipoprotein and protect it from oxidation.
Like the milk thistle herb, licorice possesses distinct hepatoprotective effects. This is thought to occur because licorice is generally cytoprotective, and in this regard can prevent changes in cell membrane permeability, induce apoptosis, suppress lipid peroxidation and the normalise liver enzymes. Licorice also possesses cytotoxic effects which may explain its reported anticancer activity, particularly against prostate cancer. Because constituents of licorice prevent anti-platelet aggregation and inhibit thrombosis in vitro, licorice may be cardioprotective. Further, isoliquiritigenin may possess the ability to cause vasodilation which may lower blood pressure. The antiinflammatory effects of licorice may also contribute to its cardioprotective effects. Glycyrrhizin stimulate immunity through a number of mechanisms including activation of T cells and interferon, and inhibition of tumor necrosis factor alpha and interleukin. Licorice may also increase 5α-reductase and aromatase, thus having a pronounced effect on steroid metabolism.