Neoandrographolide is a major diterpenoid compound found in Andrographis paniculata, a medicinal plant extensively used in traditional Asian medicine for treating respiratory infections, including influenza. Scientific interest has grown in recent decades, with several in vitro and in vivo studies investigating its antiviral and immunomodulatory properties. Research indicates that extracts of Andrographis paniculata and its constituents, including neoandrographolide, exhibit inhibitory effects against influenza viruses. Proposed mechanisms include interference with viral attachment and entry, inhibition of viral replication, and modulation of host immune responses (e.g., increasing antiviral cytokines).

However, most clinical studies have evaluated whole-plant extracts rather than isolated neoandrographolide. Systematic reviews and randomized controlled trials suggest that Andrographis paniculata extracts may reduce the severity and duration of upper respiratory tract infections, including influenza-like illnesses. Direct clinical evidence specifically for neoandrographolide against influenza in humans remains limited, and most data come from cell culture or animal models.

In summary, while there is scientific rationale and preliminary evidence supporting the use of neoandrographolide-rich extracts for influenza, the evidence level is moderate (rated 2 out of 5) due to the lack of large-scale, well-controlled clinical trials focused on the isolated compound.