Dehydrocrenatidine, a natural product isolated and purified from the barks of Picrasma quassioides, is a JAK-specific inhibitor, which inhibits JAK2-JH1 kinase activity in vitro , represses constitutively activated JAK2 and STAT3, as well as interleukin-6-, interferon-α-, and interferon-γ-stimulated JAK activity, and STAT phosphorylation, and suppresses STAT3 and STAT1 downstream gene expression.