Methods of treating, and/or improving impulse control disorder, which comprises administering to a living subject, a composition comprising chitosan as an effective ingredient, having a weight-average molecular weight of 80,000 to 100,000 and a number-average molecular weight of 30,000 to 40,000, as measured by gel permeation chromatography (GPC). Also provided are methods for giving an activity of repressing impulse to food products and drinks by putting said chitosan in the food products, drinks and the material therefor.