Gimeracil is a component of an oral fixed combination known under the name Teysuno or S-1 (tegafur, gimeracil and oteracil potassium at a molar ratio of 1:0.4:1). The formulation was approved in Asia and Europe for the treatment of a rare condition of gastric cancer. Given in combination, gimeracil enhances the efficacy of tegafur by inhibiting dihydropyrimidine dehydrogenase, an enzyme involved in metabolism of tegafur and its active metabolite 5-fluorouracil.