Vitamin U is not a vitamin. Some manufacturers and retailers use the name to describe "S-Methyl-L-methionine", a putative derivative of methionine. Mainstream nutrition science does not recognize any substance by this name. The term "Vitamin U" was derived from methionine's use as an unproven treatment for ulcers by naturopathic doctors. Its sources are claimed to be limited, and those who sell it also claim it can be found in raw cabbage. "Vitamin U" is alleged by them to fight peptic ulcers, and help heal duodenal ulcers.