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.
Cantelli-Forti G, Maffei F, Hrelia P, Bugamelli F, et al. Interaction of licorice on glycyrrhizin pharmacokinetics. Environ Health Perspect 1994 Nov;102 Suppl 9:65-68
Takeda S, Ishthara K, Wakui Y, Amagaya S, et al. Bioavailability study of glycyrrhetic acid after oral administration of glycyrrhizin in rats; relevance to the intestinal bacterial hydrolysis. J Pharm Pharmacol 1996 Sep;48(9):902-905
Utsunomiya, T. et al. Glycyrrhizin, an active component of licorice roots, reduces morbidity and mortality of mice infected with lethal doses of influenza virus. Antimicrob Agents Chemother 1997;41:551-556
Yamamura Y, Santa T, Kotaki H, Uchino K, et al. Administration-route dependency of absorption of glycyrrhizin in rats: intraperitoneal administration dramatically enhanced bioavailability. Biol Pharm Bull 1995 Feb;18(2):337-341
Y, Kawakami J, Santa T,
Kotaki H, et al. Pharmacokinetic profile of
glycyrrhizin in healthy
volunteers by a new high-performance liquid
chromatographic method. J
Pharm Sci 1992 Oct;81(10):1042-1046