Glycyrrhizinic acid, a main active compound of licorice root (Glycyrrhiza glabra), has been studied for its antiviral properties, including against influenza viruses. Several in vitro studies have demonstrated that glycyrrhizinic acid and its aglycone, glycyrrhetinic acid, can inhibit the replication of influenza A virus strains by interfering with viral attachment and penetration, as well as modulating host immune responses. A few animal studies also report reduced viral titers and decreased lung inflammation after administration of glycyrrhizinic acid. The mechanisms proposed include suppression of viral gene expression, modulation of cytokine production, and antioxidant effects.

However, the evidence supporting its use in humans is limited. There are no robust clinical trials confirming its efficacy for treating or preventing influenza in people. Most available data are preclinical (cell culture and animal models), and the translation of these findings to clinical practice remains uncertain. Furthermore, concerns about potential side effects, such as hypertension and hypokalemia due to mineralocorticoid effects, limit its widespread therapeutic use.

In summary, while there is scientific interest and preliminary laboratory evidence of antiviral activity against influenza, clinical validation is lacking. The evidence rating is 2 out of 5, reflecting promising but not yet clinically proven activity.