[2] As a prodrug to 5-FU it is used in the treatment of the following cancers:[3] It is often given in combination with drugs that alter its bioavailability and toxicity such as gimeracil, oteracil or uracil.

[3] These agents achieve this by inhibiting the enzyme dihydropyrimidine dehydrogenase (uracil/gimeracil) or orotate phosphoribosyltransferase (oteracil).

[3] The major side effects of tegafur are similar to fluorouracil and include myelosuppression, central neurotoxicity and gastrointestinal toxicity (especially diarrhoea).

[3] The dihydropyrimidine dehydrogenase (DPD) enzyme is responsible for the detoxifying metabolism of fluoropyrimidines, a class of drugs that includes 5-fluorouracil, capecitabine, and tegafur.

[5][6] Those with partial or complete DPD deficiency have a significantly increased risk of severe or even fatal drug toxicities when treated with fluoropyrimidines; examples of toxicities include myelosuppression, neurotoxicity and hand-foot syndrome.