Phellodendron bark, known as "Huang Bai" in Traditional Chinese Medicine (TCM), has a long history of use for various ailments, particularly for its purported "heat-clearing" and "dampness-drying" properties. In TCM, it is commonly prescribed for infections, inflammatory conditions, and symptoms such as fever, which may overlap with those seen in influenza. However, its use for influenza specifically is grounded in traditional practices rather than direct historical or modern scientific evidence targeting the influenza virus itself.

Scientifically, laboratory studies have identified some antimicrobial and anti-inflammatory constituents in Phellodendron bark, such as berberine, but there is a lack of well-conducted clinical trials or robust preclinical studies demonstrating efficacy against the influenza virus. The bark is not recognized in mainstream medicine as a treatment for influenza, and authoritative pharmacopoeias or guidelines do not list it as a standard remedy for influenza.

In summary, the use of Phellodendron bark for influenza is justified primarily by traditional use within TCM frameworks rather than by strong scientific validation or clinical evidence. The evidence supporting its use for this indication is weak (rated 1), reflecting primarily anecdotal or historical use rather than substantiated, targeted efficacy.