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 meta-analysis of 5 randomized trials (609 patients) reported that topical licorice prior to endotracheal intubation prevented postoperative sore throats by 56% and cough by 39% (4). In a randomized 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 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). In another randomized trial including 70 adults, licorice pastilles (lozenges) versus placebo were shown to help chronic cough symptoms (6). Licorice has also been administered as adjunct therapy to decrease symptoms of Parkinson disease (7).

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. A pooled analysis reported that chronic licorice intake may be associated with increased systolic and diastolic blood pressure (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. A pooled analysis reported that chronic licorice intake may be associated with increased systolic and diastolic blood pressure (8).

Licorice may have steroidal and estrogenic effects in pregnancy and may also increase the risk of preterm delivery. High licorice consumption during pregnancy may stimulate hypothalamic pituitary adrenocortical activity in the child 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 medications 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 class of antidepressant called monoamine oxidase (MAO) inhibitors and thus may intensify adverse effects of these medications.

(See table Some Possible Dietary Supplement–Medication 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

6. 6. Ghaemi H, Masoompour SM, Afsharypuor S, Mosaffa-Jahromi M, Pasalar M, Ahmadi F, Niknahad H. The effectiveness of a traditional Persian medicine preparation in the treatment of chronic cough: A randomized, double-blinded, placebo-controlled clinical trial. Complement Ther Med. 2020 Mar;49:102324. doi: 10.1016/j.ctim.2020.102324

7. 7. Petramfar P, Hajari F, Yousefi G, Azadi S, Hamedi A. Efficacy of oral administration of licorice as an adjunct therapy on improving the symptoms of patients with Parkinson's disease, A randomized double blinded clinical trial. J Ethnopharmacol. 2020 Jan 30;247:112226. doi: 10.1016/j.jep.2019.11222

8. 8. Penninkilampi R, Eslick EM, Eslick GD. The association between consistent licorice ingestion, hypertension and hypokalaemia: a systematic review and meta-analysis. J Hum Hypertens. 2017 Nov;31(11):699-707. doi: 10.1038/jhh.2017.45

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: Licoric Root