Buy online Ritalin is a central nervous system stimulant. Methylphenidate affects chemicals in the brain and nerves that contribute to hyperactivity and impulse control .The brand names of this medication are Methylin r and Ritalin. It is a uncoated tablet. It is a white coated round tablet marked CG on right side. AB with a Breakline in the middle. Its diameter is ca. 7.1 mm thickness and ca 2.6mm.