5,6-Dihydro-5-methyluracil (Dihydrothymine), an intermediate breakdown product of thymine, comes from animal or plants. 5,6-Dihydro-5-methyluracil (Dihydrothymine) can be toxic when present at abnormally high levels[1]. Human Endogenous Metabolite
[1]. Yamane T, et al. Dihydrothymine from UV-irradiated DNA. Proc Natl Acad Sci U S A. 1967 Aug;58(2):439-42.