The purpose of this study was to determine the levels of leptin, ghrelin, and nesfatin-1 to elucidate the causes of poor appetite and growth retardation in patients receiving methylphenidate therapy for attention deficit hyperactivity disorder. The study was performed on 89 male subjects; 48 patients and 41 healthy controls, aged 7-14 years. Following treatment, patients' leptin-levels increased and ghrelin levels decreased while no-significant change was found in nesfatin-1 levels. Of the 48 patients, 34 developed lack of appetite. In patients who developed lack of appetite, body weight SDS, body mass index (BMI), and BMI SDS were statistically significantly reduced; moreover, height SDS was reduced, though not to a statistically significant extent. This study attempted to elucidate the mechanisms that mediate the association between methylphenidate and appetite and growth, for which no studies have yet to be published.