Ritalinic acid is an inactive, major metabolite of methylphenidate, a schedule II drug in the United States commonly used as a psychostimulant drugs methylphenidate and ethylphenidate. The elimination half-life of methylphenidate is relatively short (approximately 2 hours); therefore it is also available in extended release (ER) forms. The main metabolite is ritalinic acid, and the methylphenidate metabolites are mostly excreted in urine.