1,3-dimethyl-7H-purine-2,6-dione; 3,9-Dihydro-1,3-dimethyl-1H-purine-2,6-dione; 3,7-Dihydro-1,3-dimethyl- 1H-purine- 2,6-dione (USP); Caffeine EP Impurity A; 1H-Purine-2,6-dione, 3,7-dihydro-1,3-dimethyl; Dimenhydrinate EP Impurity A