Glycyrrhizin, a major active component of licorice root (Glycyrrhiza glabra), has a long history of use in traditional medicine for respiratory ailments, including colds. More recently, scientific studies have explored its antiviral properties. In vitro and some animal studies have demonstrated that glycyrrhizin exhibits activity against various viruses, including those responsible for respiratory tract infections, such as influenza and some coronaviruses. The proposed mechanisms include interference with viral replication, inhibition of viral gene expression, and modulation of the host immune response.

Despite these promising preclinical findings, there is limited high-quality clinical evidence to support glycyrrhizin's effectiveness in treating or preventing the common cold in humans. Most clinical research has focused on its use in chronic viral infections (e.g., hepatitis), with only a few small studies suggesting potential benefit for acute respiratory infections. Reviews note that while the laboratory data are encouraging, robust human trials are lacking, and the safety of glycyrrhizin—especially with long-term or high-dose use—remains a concern due to risks like hypertension and hypokalemia.

In summary, glycyrrhizin's use for colds is supported by preclinical antiviral data and traditional use, but clinical evidence in humans is limited and not definitive. The overall scientific evidence rating is moderate to low (2/5), reflecting promising laboratory results but insufficient clinical validation.