Glycyrrhiza glabra - Licorice Root: Effects & Uses

What is Glycyrrhiza glabra?

Glycyrrhiza glabra, commonly known as licorice or licorice root, is a perennial medicinal and useful plant belonging to the legume family (Fabaceae). It is native to the Mediterranean region, the Middle East, and Central Asia. The dried root of the plant has been used for thousands of years in both traditional and modern medicine. The Latin species name glabra means “smooth” and refers to the plant’s hairless leaves.

Active Compounds and Constituents

The root of Glycyrrhiza glabra contains numerous bioactive compounds responsible for its pharmacological properties:

• Glycyrrhizin (glycyrrhizinic acid): The main active compound, a triterpenoid saponin constituting approximately 5–15% of the dry weight of the root. It is about 50 times sweeter than sucrose and is responsible for many of the medicinal effects as well as potential side effects.
• Glabridin: An isoflavonoid with antioxidant, anti-inflammatory, and skin-brightening properties.
• Liquiritin and isoliquiritin: Flavonoids with anti-inflammatory and antioxidant activity.
• Glycyrrhetinic acid: The active metabolite of glycyrrhizin in the body, with potent anti-inflammatory and immunomodulatory effects.
• Polysaccharides, essential oils, and coumarins: Additional secondary plant compounds with synergistic effects.

Mechanism of Action

The pharmacological activity of Glycyrrhiza glabra is multifaceted and is mainly based on the properties of glycyrrhizin and its metabolites:

• Anti-inflammatory: Glycyrrhizin and glycyrrhetinic acid inhibit pro-inflammatory enzymes (e.g., phospholipase A2, cyclooxygenase) and the release of inflammatory mediators such as prostaglandins and leukotrienes.
• Antiviral: Glycyrrhizin has demonstrated antiviral activity against various viruses, including herpes simplex virus, influenza viruses, and hepatitis C virus, partly by inhibiting viral replication.
• Mucosal protection (demulcent): Licorice extract promotes mucus production in the gastrointestinal tract, thereby protecting the mucosa from irritation and stomach acid.
• Expectorant and antitussive: Licorice root helps liquefy mucus in the airways, making it easier to cough up.
• Immunomodulation: Certain constituents can modulate the immune system and exhibit adaptogenic properties.
• Inhibition of cortisol breakdown: Glycyrrhizin inhibits the enzyme 11-beta-hydroxysteroid dehydrogenase type 2, allowing cortisol to remain active in the body for longer. This explains both anti-inflammatory effects and side effects such as elevated blood pressure at high doses.

Traditional Use

Glycyrrhiza glabra is one of the oldest known medicinal plants in human history. In Traditional Chinese Medicine (TCM), licorice has been used for over 4,000 years as a “harmonizing herb” that enhances the effects of other remedies. In Ayurveda (Indian medicine), the plant is known as Yashtimadhu and is used for respiratory and digestive conditions. Licorice also played a significant role in European folk medicine during the Middle Ages as a remedy for coughs, sore throats, and stomach problems.

Medical Applications

Based on scientific studies and traditional experience, Glycyrrhiza glabra is used for the following conditions:

Respiratory Conditions

Licorice root extract is commonly used for coughs, bronchitis, sore throats, and catarrh of the upper respiratory tract. Its expectorant and soothing effects are well documented. The European Pharmacopoeia lists licorice root as an official drug for this indication.

Gastrointestinal Disorders

Supported by both tradition and clinical studies, licorice is used for gastritis, peptic ulcers, acid reflux (GERD), and irritable bowel syndrome. Deglycyrrhizinated licorice (DGL) is a widely used supplement form from which glycyrrhizin has been largely removed to minimize side effects.

Liver Protection and Antiviral Effects

In hepatology (the study of liver diseases), intravenous glycyrrhizin is used as a supportive therapy for chronic hepatitis B and C, particularly in Japan. Studies demonstrate hepatoprotective (liver-protecting) effects.

Skin and Topical Applications

Glabridin from licorice is used in dermatology and cosmetics for its antioxidant, anti-inflammatory, and skin-brightening properties. It is applied in cases of hyperpigmentation, eczema, and atopic dermatitis.

Further Potential Applications

Current research is investigating the potential of Glycyrrhiza glabra in:

• Metabolic syndrome and type 2 diabetes (blood sugar-lowering effects of glabridin)
• Neurodegenerative diseases (antioxidant protection)
• Antiviral therapy (e.g., COVID-19 research)
• Hormonal disorders (mild estrogenic activity of isoflavonoids)

Dosage and Administration

The recommended dosage of licorice root varies depending on the form and indication:

• Tea (infusion): 1–5 g of dried root per cup, up to 3 times daily
• Standardized extract: According to manufacturer instructions; typically 200–600 mg dry extract per day
• DGL tablets (deglycyrrhizinated): 380–1,140 mg before meals for gastrointestinal complaints
• Duration of use: The European Medicines Agency (EMA) and the Committee on Herbal Medicinal Products (HMPC) recommend that licorice products containing glycyrrhizin should not be taken for longer than 4–6 weeks without medical supervision.

Side Effects and Safety

At moderate, short-term doses, Glycyrrhiza glabra is generally considered well tolerated. However, excessive or long-term use may lead to serious adverse effects:

• Pseudohyperaldosteronism: Glycyrrhizin inhibits cortisol breakdown and produces an aldosterone-like effect: sodium and water retention, potassium loss (hypokalemia), high blood pressure, and edema.
• Cardiac arrhythmias: Hypokalemia may trigger heart rhythm disturbances.
• Muscle weakness: As a consequence of potassium loss.
• Hormonal effects: Due to mild estrogenic activity, individuals with estrogen-dependent conditions (e.g., breast cancer) should avoid licorice.

Contraindications

Glycyrrhiza glabra (with glycyrrhizin) should not be used in cases of:

• High blood pressure (hypertension)
• Severe liver or kidney disease
• Hypokalemia (potassium deficiency)
• Pregnancy and breastfeeding
• Heart failure or cardiac arrhythmias
• Estrogen-dependent tumors

Interactions

Licorice may interact with various medications and substances:

• Antihypertensives: Reduced effectiveness due to the blood pressure-raising effect of glycyrrhizin
• Diuretics: Increased potassium loss
• Corticosteroids: Potentiation of effects and side effects
• Cardiac glycosides (e.g., digoxin): Increased risk of toxicity due to hypokalemia
• Oral contraceptives: Possible interactions due to hormonal effects

References

1. European Medicines Agency (EMA) / HMPC: Assessment report on Glycyrrhiza glabra L. and/or Glycyrrhiza inflata Bat. and/or Glycyrrhiza uralensis Fisch., radix. EMA/HMPC/571119/2010. London, 2012.
2. Fiore, C. et al.: A history of the therapeutic use of liquorice in Europe. Journal of Ethnopharmacology, 99(3), 317–324, 2005. DOI: 10.1016/j.jep.2005.04.015
3. Pastorino, G. et al.: Liquorice (Glycyrrhiza glabra): A phytochemical and pharmacological review. Phytotherapy Research, 32(12), 2323–2339, 2018. DOI: 10.1002/ptr.6178