Glycyrrhiza: Glycyrrhizin and influenza
by Paul Bergner
Medical Herbalism 10(1-2):37
An animal trial has shown that glycyrrhizin, a major constituent of licorice root (Glycyrrhiza glabra), completely protected a group of mice which had been injected with a lethal dose of influenza virus (Utsunomiya et al). The glycyrrhizin was injected into the peritoneum (abdominal cavity) of the mice. The researchers determined that glycyrrhizin’s effect was probably due to the stimulation of the effects of gamma-interferon, an anti-viral immune component. Before we go filling our flu patients with licorice tea or tincture, note that glycyrrhizin when taken by the oral route is mostly transformed (99%) into glycyrrhetic acid (Cantelli-Forti et al; Takeda et al.), which has no recognized antiviral effects. One trial in healthy volunteers found no glycyrrhizin in the plasma after oral administration (Yamamura et al, 1992). Intraperitoneal injection of glycyrrhizin rather than oral administration of licorice root was probably selected because a previous trial showed this to be the most efficient way to maximize plasma levels of glycyrrhizin (Yamamura et al, 1995).
In traditional Chinese medicine, licorice is classified as a chi tonic, and must be used with caution in acute illnesses with strong symptoms to prevent intensifying those symptoms. The phenomenon, “tonifying the illness” routinely watched for and avoided in TCM. Licorice may be a valuable addition when used traditionally in a formula for dry cough, such as may accompany influenza, but a strategy of giving large doses because of supposed antiviral effects may be counterproductive.
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