Involved in pyrimidine base degradation (PubMed:1512248). Catalyzes the reduction of uracil and thymine (PubMed:1512248). Also involved the degradation of the chemotherapeutic drug 5-fluorouracil (PubMed:1512248). 5,6-dihydrouracil + NADP(+) = H(+) + NADPH + uracil 5,6-dihydrothymine + NADP(+) = H(+) + NADPH + thymine Binds 2 FAD. Binds 2 FMN. Binds 4 [4Fe-4S] clusters. Contains approximately 16 iron atoms per subunit. Inactivated by 5-iodouracil. Amino-acid biosynthesis; beta-alanine biosynthesis. Homodimer. Found in most tissues with greatest activity found in liver and peripheral blood mononuclear cells. The disease is caused by variants affecting the gene represented in this entry. Belongs to the dihydropyrimidine dehydrogenase family.