Licorice comes from the roots of the plant Glycyrrhiza. The licorice root is typically processed into a powder or extract, which is then used in supplements, foods, and beverages. There are approximately 300 bioactive compounds in licorice root. Many of these compounds have neuroprotective antioxidant and anti-inflammatory properties, but licorice use was not associated with improved cognition in clinical studies. Glycyrrhizin is the major bioactive compound, but it can cause cardiovascular side effects, such as high blood pressure, so some licorice preparations remove it. Overconsumption of licorice increases the risk for side effects. Licorice root products are commonly used for digestive problems, menopausal symptoms, and infections.
Licorice root has been tested in a few small clinical trials, but the preparations vary across studies. Since it is most often used in combination with other medicinal herbs, any potential benefits cannot be conclusively tied to licorice.
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Licorice root has not been found to protect against cognitive decline in clinical studies. Preclinical studies have found that some of the major bioactive compounds (e.g. glycyrrhizin and glabridin) have antioxidant and anti-inflammatory effects in the brain. Liquiritigenin, the major bioactive compound capable of getting into the brain, has some estrogen-like properties [1; 2]. Its use as part of an herbal combination was associated with a reduction in menopausal symptoms, such as hot flashes, in a clinical trial [3]. While liquiritigenin improved cognitive function in a manner similar to estrogen in rodent models of menopause [4], it has not been determined whether it can protect against menopausal related cognitive dysfunction in humans. The different outcomes between the clinical and preclinical studies may relate to differences in preparation, dose, and the use of a single bioactive compound versus the mixture of hundreds of compounds found in whole licorice.
As part of the traditional Japanese medicine yokukansan, which contains the G. uralensis species of licorice root in combination with six other medicinal herbs, licorice was found to benefit agitation and irritability in two small clinical studies [5; 6]. However, licorice did not benefit cognitive function as part of yokukansan in patients with Alzheimer’s disease [5; 6], or in the form of glycyrrhizin-containing licorice syrup in patients with Parkinson’s disease [7].
Licorice is generally recognized as safe; however, excessive consumption can cause cardiovascular side effects. Glycyrrhizin, the major bioactive compound in licorice, can disrupt the balance of electrolytes in the body. It can increase sodium and decrease potassium levels, which can lead to high blood pressure and irregular heartbeat. The European Commission has set a recommended daily limit of 100 mg of glycyrrhizin, which is approximately equal to 60 to 70 g of glycyrrhizin-containing licorice [8]. Glycyrrhizin-containing licorice has drug interactions with digoxin, warfarin, cyclosporine, and a food interaction with grapefruit. Licorice oils that lack glycyrrhizin were found to be safe to consume up to 1200 mg/day in a clinical trial [9].
NOTE: This is not a comprehensive safety evaluation or complete list of potentially harmful drug interactions. It is important to discuss safety issues with your physician before taking any new supplement or medication.
Licorice root powder and extracts are primarily derived from the plant species G. glabra, G. inflanta, and G. uralensis, and are used as a flavoring for beverages and confections. The compound profile of a given batch of licorice root extract depends on the species, growing conditions, and extraction process. Licorice supplements are available with or without glycyrrhizin. The glycyrrhizin content is usually indicated on licorice supplements, but not listed on licorice containing food and beverages, where the amount of glycyrrhizin could potentially vary widely. There is no established therapeutic dose for licorice-containing products, but overconsumption increases the risk for side effects.