Metformin reduces the expression levels of NOX4, SMAD phosphorylation, and αSMA with concomitant attenuation of lung fibrosis in BLM treatment, suggesting that the anti-fibrotic mechanism of metformin is mainly attributable to inhibition of TGF-β-mediated myofibroblast differentiation. The gene discussed is NOX4; the disease is pulmonary fibrosis.