A method of treating an oxidative stress disease includes orally or intragastrically administering, to a subject in need thereof, a pharmaceutical composition including edaravone with a time interval from a consumption of a meal by the subject in need thereof to an administration of the pharmaceutical composition to the subject in need thereof. The time interval is 8 hours or longer after the consumption of a high-fat meal, the time interval is 4 hours or longer after the consumption of a standard meal, or the time interval is 2 hours or longer after the consumption of a light meal.