Licorice has been used in Traditional Chinese Medicine (TCM) since time immemorial as a key ingredient for pandemic formulas. It was a component in TCM formulas for SARS Cov-1 prevention and treatment. Along with astragalus, it is the most frequently used botanical in TCM formulas for SARS Cov-2 prevention in China. Multiple clinical trials have demonstrated its effectiveness as a part of TCM formulas for Cov-1 and H1N1.
Numerous in-vitro studies have shown the major active constituent of licorice, glycyrrhizin, to be effective against SARS Cov-1.
Impressively, a 2003 study published in Lancet looking at two clinical isolates of coronavirus from patients with SARS Cov-1 identified glycyrrhizin, to be the most active in inhibiting viral replication as compared to ribavirin, 6-azauridine, pyrazofurin, and mycophenolic acid.
A preprint molecular docking study suggests that the major active constituent, glycyrrhizin, can bind the ACE2 receptor, and therefore may have anti-SARS Cov-2 activity.
A recent free full-text review on the therapeutic potential of glycyrrhizin for COVID-19 includes the below figure illustrating potential mechanisms of action:
“Figure 1. SARS-CoV-2 invade human alveolar epithelial cells via the ACE2 receptor and cause exaggerated and aberrant host immune responses. The exaggerated immune responses lead to the over production of proinflammatory cytokines and ROS, which might cause functional disability and even death. Exaggerated inflammation could also activate coagulation and spark a surge of airway exudates which contribute to multiple organ failure and anoxia state in COVID-19 patients. Glycyrrhizin might possess therapeutic benefits for COVID-19 with multisite mechanisms, including: a) Binding ACE2 to prevent the infection of SARS-CoV-2. b) Down-regulating proinflammatory cytokines. c) Inhibiting the accumulation of intracellular ROS. d) Inhibiting thrombin. e) Inhibiting the hyperproduction of airway exudates. f) Inducing endogenous interferon to combat the SARS-CoV-2.”
Licorice is considered a botanical of low toxic potential and has been safely used in TCM for millennia. However, excessive ingestion (here’s a classic case report from NEJM, where the patient had been ingesting 60-100 grams of licorice candy daily for 4-5 years), can exert an aldosterone-like effect resulting in potassium wasting. Prescribing glycyrrhizin in individuals on potassium wasting medications may result in hypokalemia.
It’s also important to note that SARS Cov-2 itself has been associated with potassium wasting, (1) as has hydroxychloroquine, a drug whose utility against COVID19 is still being investigated.
Thus, while glycyrrhizin may be a very important COVID19 intervention, serum potassium should be monitored (and potassium prescribed as needed) to assure hypokalemia is avoided in vulnerable individuals. Note that ingesting potassium-containing foods is a safe, smart way to access potassium.
Dosage: From the German Commission E monograph, the average daily dosage prescribed is 5 g to 15 g of root, equivalent to 200 to 600 mg of glycyrrhizin or equivalent preparations.
A couple of additional thoughts:
Licorice has also been used in the West for centuries. From Plant Medicine in Practice: Using the Teaching of John Bastyr, the indications for licorice are broad: allergies, antiseptic, antiviral, anti-inflammatory, adrenal gland support, and expectorant/respiratory support. With long term licorice use, Dr. Bastyr recommended taking 100mg potassium bid. In 1953, The Lancet reported on the synergistic action of licorice and cortisone in Addison’s disease.
Despite its very impressive list of bioactive constituents and its long, safe use history in traditional medicine across the globe, some readers run from licorice because of its potassium wasting and hypertension inducing potential. Licorice’s effect is a little more nuanced, however. While it does exert an aldosterone-like effect, it’s actually potently anti-androgenic and appears to work synergistically with spironolactone in PCOS. Here’s a nice review to explore if you’re interested.