Common Names
- Gan cao
- Sweet root
- Glycyrrhiza
- Liquorice
For Patients & Caregivers
How It Works
Licorice may be helpful in treating peptic ulcers, but it has not been shown effective in treating cancer.
In traditional Chinese medicine, licorice is often used in herbal formulas to harmonize the effects of other herbs. Experiments in animals and humans show licorice can mimic the effects of steroid hormones such as aldosterone and estrogen. The substance in licorice that scientists think is responsible for these effects is called glycyrrhizin. However, because glycyrrhizin causes undesirable side effects, it is often removed from licorice products during processing.
Physiologic activity has also been reported for several other compounds in licorice. Isoflavone compounds also mimic estrogens in the human body, and can kill several strains of bacteria and viruses on contact. Other compounds act as blood thinners and inhibit inflammation. In humans, the compound, carbenoxolone, has been used to treat stomach and esophageal ulcers with positive effects. Scientists think that it increases blood flow to and amount of mucus lining the stomach.
Purported Uses
- To treat bronchitis and chest congestion
No scientific evidence supports this use. - To relieve constipation
This claim is not backed by research. - To treat gastrointestinal disorders such as peptic ulcers
A substance in licorice called carbenoxolone decreased pain and heartburn and increased healing in patients with peptic ulcers, but major side effects including fluid accumulation, low potassium, and high blood pressure were reported. - To treat hepatitis
Clinical trials in Japan have used a licorice extract containing glycyrrhizin to treat hepatitis B and C, and have shown that glycyrrhizin reduces liver disease. However, there is no proof that deglycyrrhizinated licorice would have the same effect. - To reduce inflammation
Studies in animals support this use, but there is no proof from clinical trials that this effect occurs in humans. - To relieve menopausal symptoms
Studies in animals show that licorice has estrogenic effects, and some of the components of licorice bind estrogen receptors. Human data are lacking. - To treat microbial infections
Studies in animals suggest that licorice has antimicrobial activity, but human data are lacking. - To treat prostate cancer
No scientific evidence supports this use. Licorice is an ingredient in PC-SPES, which has been studied in patients with prostate cancer.
Do Not Take If
- You take cardiac glycosides: Licorice may increase their effects and cause toxicity.
- You take insulin: Licorice may increase the sugar lowering effect.
- You take diuretic drugs: Licorice may lower the blood potassium level.
- You take warfarin or other blood thinners: Licorice may increase the risk of bleeding.
- You take MAO-inhibitors (MAOIs): Licorice may have additive effects.
- You take daunorubicin: Licorice intake can result in increased intracellular concentration of daunorubicin, which may increase its toxic effects.
- You are taking cytochrome P450 substrates: Licorice may affect the actions of these drugs.
- You are taking cyclosporine: Licorice greatly reduced the oral bioavailability of cyclosporine by activating P-gp and CYP3A4, which can make it less effective.
- You are taking cortisol acetate: Licorice increased cortisol availability in tissues, which may increase its side effects.
- You are taking metformin: Pre-administration of licorice juice reduced the efficacy of metformin, in a rat model. Whether similar effect occurs in humans is not known
Side Effects
Special Point
For Healthcare Professionals
Clinical Summary
Derived from the root of the plant, licorice has been used as a flavoring and sweetening agent. This herb is an important component of traditional Chinese medicine used to detoxify and enhance or balance the effects of other components in herbal formulas; and as a tonic, expectorant and a demulcent in Ayurveda. A number of compounds including glycyrrhizin are thought to be responsible for its biologic effects.
In vitro and animal studies show that licorice has antibacterial (2) (27), antiviral (48), anticancer (3) (4) (28) (29), anti-inflammatory (30), and hepatoprotective (49) properties. Licorice also demonstrated estrogenic effects (10), reduced cardiotoxicity associated with doxorubicin (31), and improved the antitumor effects of cyclophosphamide (32). However, these effects have not been confirmed in humans.
Clinical data suggest utility of licorice in lowering dyspepsia (1) and hyperlipidemia (33), and concurrent intake of a glycyrrhizin-containing product during alcohol consumption was shown to afford hepatoprotection (50). In another study, preoperative gargling with licorice solution affected significant reductions in postoperative sore throat when compared to gargling with sugar water (51). Licorice solution was also reported to improve xerostomia in hemodialysis patients (52); and had comparable efficacy as triamcinolone in the management of oral mucositis during radiotherapy (53). But chronic ingestion of even moderate doses of licorice has been associated with hypertension and hypokalemia (54).
Purported Uses
Mechanism of Action
Glycyrrhizin, one of the bioactive compounds of licorice, has been shown to bind to glucocorticoid and mineralocorticoid receptors, and exert its effects via inhibition of 11b-hydroxysteroid dehydrogenase (12). Licorice can reduce serum testosterone by inhibiting 17-hydroxysteriod dehydrogenase (35) (36). It also contains isoflavones and other constituents that have estrogen receptor-modulating activities (10). The flavone and liquiritigenin components selectively activate ER-alpha (11).
Liquiritigenin was also shown to have neuroprotective effects in scopolamine-induced mice likely via increasing expression of brain-derived neurotrophic factor (BDNF), and phosphorylation of extracellular signal-regulated kinase (ERK) and cAMP response element binding (CREB) in the hippocampus (55). In addition, glycyrrhizic acid, a triterpene glycoside, demonstrated anti-allerigic property by restoring the immune balance of subsets 1 and 2 of T helper cells in a dose-dependent manner. It also siginificantly reduced B cells producing allergen-specific IgE and IgG1 (56).
In other studies, licorice demonstrated chemo-preventive effects by modulating expression of Bcl-2/Bax proteins, which act as apoptotic regulatory factors (3); and via inhibiting carcinogenesis (4). The most common side effect of licorice is hypokalemic hypertension, which occurs secondary to inhibition of 11beta-hydroxysteroid dehydrogenase, a renal enzyme responsible for converting cortisol to cortisone. This inhibition results in enhancing the mineralocorticoid effects of cortisol (36) that include sodium retention and excretion of potassium.
Warnings
Adverse Reactions
Hypertension (16) (45) (57), lethargy, muscle pain, sodium retention, hypokalemia (17) (18) (19) (20) (26) (41), adrenal crisis (21), ventricular fibrillation (22), cardiac arrythmias (23), carpal tunnel syndrome (24), glycyrrhizic acid poisoning (25), leukoderma (42), and thrombocytopenia (43)have been reported following ingestion of licorice or licorice containing products.
Herb-Drug Interactions
Cardiac glycosides: Licorice may potentiate toxicity (24).
Diuretics: Licorice may increase the risk of hypokalemia (17) (18).
Insulin: Licorice may increase insulin sensitivity (38) .
Anticoagulants: Licorice may increase the metabolism and clearance of warfarin (19).
MAO-inhibitors (MAOIs): Licorice may potentiate activity of MAOIs (37)
P-Glycoprotein (P-gp) substrates: Licorice inhibited P-gp, resulting in increased intracellular concentration of the chemotherapy agent daunorubicin, which is a substrate of P-gp (34).
Cytochrome P450 substrates: Glycyrrhizin, a major constituent of licorice, induces CYP3A (39) and CYP2D6 (44), and can affect the intracellular concentration of drugs metabolized by this enzyme. However, other constituents, like glabridin, glycycoumarin and licochalcone A from different species of licorice can inhibit these enzymes (40).
Cyclosporine: Licorice greatly reduced the oral bioavailability of cyclosporine by activating P-gp and CYP3A4 (46).
Cortisol acetate: Licorice increased cortisol availability in tissues in the hours following oral cortisone acetate administration (47).
Metformin: Pre-administration of licorice juice reduced the efficacy of metformin, in a rat model (58). The clinical relevance in humans has yet to be determined.