Licorice

People most often take licorice to suppress coughs, to soothe a sore throat, and to relieve stomach upset. Applied externally, it is said to soothe aphthous ulcers and skin irritation (eg, eczema) (1). Licorice has also been claimed to help treat stomach ulcers and complications caused by hepatitis C or other liver diseases (2).

Evidence indicates that licorice in combination with other herbs provides relief from the symptoms of functional dyspepsia and irritable bowel syndrome (3). However, clinical trials of both licorice alone and in combination are limited, and further evaluation is required. There are not enough data to determine whether licorice is effective for stomach ulcers or complications caused by hepatitis C.

A review and meta-analysis of 5 randomized controlled trials (609 subjects) reported that topical licorice prior to endotracheal intubation prevented postoperative sore throats by 56% and cough by 39% (4). In a randomized controlled trial in 70 people with aphthous ulcers, licorice plus diphenhydramine solution was compared to diphenhydramine monotherapy. The main result was a faster healing time in patients treated with licorice plus diphenhydramine solution (). In a randomized controlled trial in 70 people with aphthous ulcers, licorice plus diphenhydramine solution was compared to diphenhydramine monotherapy. The main result was a faster healing time in patients treated with licorice plus diphenhydramine solution (5).

At lower dosages or normal consumption levels, few adverse reactions are evident. However, high doses of real licorice (> 1 oz per day) and glycyrrhizin cause renal sodium and water retention, possibly leading to high blood pressure, and potassium excretion, possibly causing low potassium levels (pseudoaldosteronism). Increased potassium excretion can be a particular problem for people who have heart disease and for those who take digoxin or diuretics that also increase potassium excretion. Such people and those who have high blood pressure should avoid taking licorice.At lower dosages or normal consumption levels, few adverse reactions are evident. However, high doses of real licorice (> 1 oz per day) and glycyrrhizin cause renal sodium and water retention, possibly leading to high blood pressure, and potassium excretion, possibly causing low potassium levels (pseudoaldosteronism). Increased potassium excretion can be a particular problem for people who have heart disease and for those who take digoxin or diuretics that also increase potassium excretion. Such people and those who have high blood pressure should avoid taking licorice.

Licorice may increase the risk of premature delivery; thus, pregnant women should avoid licorice.

Licorice may

• Interact with warfarin and decrease its effectiveness, increasing the risk of blood clottingInteract with warfarin and decrease its effectiveness, increasing the risk of blood clotting

• Interact with digoxin by affecting potassium levelsInteract with digoxin by affecting potassium levels

• Decrease effectiveness of antihypertensive drugs due to an increase in salt and water retention

• Decrease effects of paclitaxel and cisplatinDecrease effects of paclitaxel and cisplatin

• Increase adverse effects of corticosteroids

• Increase or decrease effects of estrogens

Also, some experts believe that licorice has some activity similar to a type of antidepressant called monoamine oxidase (MAO) inhibitors and thus may intensify adverse effects of these drugs.

(See table Some Possible Dietary Supplement–Drug Interactions.)

1. 1. Saeedi M, Morteza-Semnani K, Ghoreishi MR: The treatment of atopic dermatitis with licorice gel. J Dermatolog Treat 14(3):153-157, 2003. doi:10.1080/09546630310014369

2. 2. Li X, Sun R, Liu R: Natural products in licorice for the therapy of liver diseases: progress and future opportunities. Pharmacol Res 144:210-226, 2019. doi: 10.1016/j.phrs.2019.04.025

3. 3. Ottillinger B, Storr M, Malfertheiner P, et al: STW 5 (Iberogast^®)—a safe and effective standard in the treatment of functional gastrointestinal disorders. Wien Med Wochenschr 163(3-4): 65-72, 2013. doi: 10.1007/s10354-012-0169-x

4. 4. Kuriyama A, Maeda H: Topical application of licorice for prevention of postoperative sore throats in adults: a systematic review and meta-analysis. J Clin Anesth 54:25-32, 2019. doi: 10.1016/j.jclinane.2018.10.025

5. 5. Akbari N, Asadimehr N, Kiani Z: The effects of licorice containing diphenhydramine solution on recurrent aphthous stomatitis: a double-blind, randomized clinical trial. : The effects of licorice containing diphenhydramine solution on recurrent aphthous stomatitis: a double-blind, randomized clinical trial.Complement Ther Med 50:102401, 2020. doi:10.1016/j.ctim.2020.102401

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

1. National Institutes of Health (NIH), National Center for Complementary and Integrative Health: General information on the use of licorice root as a dietary supplement