Isoimperatorin is a tumor necrosis factor antagonist isolated from Glehniae root or from Poncirus trifoliate Raf (L579). Furocoumarins, are phototoxic and photocarcinogenic. They intercalate DNA and photochemically induce mutations. Furocoumarins are botanical phytoalexins found to varying extents in a variety of vegetables and fruits, notably citrus fruits. The levels of furocoumarins present in our diets, while normally well below that causing evident acute phototoxicity, do cause pharmacologically relevant drug interactions. Some are particularly active against cytochrome P450s.