Diffractaic acid is a lichen metabolite that has been found in P. magellanica and has diverse biological activities. It is cytotoxic to HCT116, HeLa, and MCF-7 cancer cells (IC50s = 42.2, 64.6, and 93.4 μM, respectively). Diffractaic acid inhibits growth of M. tuberculosis (MIC = 41.7 μM). In vivo, diffractaic acid (25-200 mg/kg) reduces neutrophil infiltration, lipid peroxidation, myeloperoxidase (MPx) activity, and the number of gastric lesions as well as reverses decreases in superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities induced by indomethacin in rat gastric mucosa. Diffractaic acid also has analgesic activity, reducing acetic acid-induced writhing and increasing the pressure pain threshold in mice.