Licorice contains compounds that are valuable in inhibiting some viruses, but it is not clear that it would be beneficial for the H5N1. Glycyrrhizin, a sweet tasting component of licorice root, has been shown to help fight a variety of influenza, herpes, hepatitis and other viruses.

In a study on mice given a lethal dose of H2N2 influenza virus, glycyrrhizin led to 100% survival if administered one day before and 1 and 4 days after exposure to the virus. When gamma-interferon was blocked with a monoclonal antibody, glycyrrhizin had no protective effect. PMID:9055991 (cache).

In the past, virus for vaccines were often grown in eggs (which is why people with allergies to eggs are cautioned about the vaccine). In a study where such infected eggs were injected with glycyrrhizin, the viruses produced markedly less hemagluttinin, a protein associated with the spread of influenza viruses. This study noted that the viruses were still viable and virus hemagglutinating activity was not affected, but it raises the possibilty that some of the antiviral activity of licorice is related to this interference with hemagluttinin. PMID:6633273 (cache).

In a study on pigs, the H5N1 virus was resistant to interferons and TNF that inhibited other influenza viruses. PMID:15163498 (cache). The same is true in humans, and the high fatality rate is due (at least in part) to over-secretion of TNF and other cytokines. This calls into question the use of licorice glycyrrhizin for H5N1 infections.

On the other hand, glycyrrhizin reduces the production of the inflammatory cytokines IL-8 and eotaxin in lung fibroblast cells. If it can be shown that the H5N1 increases levels of these cytokines, then licorice may be beneficial. PMID:15454116 (cache) Unfortunately, a preliminary search of the medical literature indicates that the role of IL-8 and eotaxin in avian flu has not been studied.

At this point, the value of glycyrrhizin for H5N1 is unclear.

Glycyrrhizin can raise blood pressure in some individuals and should be used with care.

Licorice candy in the United States often contains no licorice what so ever; anise is used as a cheap flavoring substitute.

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