In games, immediate affects are a given. You take a potion, your wounds vanish instantly as your HP recovers. Poison is cured instantly with antidotes. Status enhancing items take affect the moment consumed. Thanks to the <Game Character's Body> right when Ryutaro swallowed the aspirin, before he could get into bed even, he found his headache gone instantly. All traces of it seemed to completely vanish as the Item seemed to cure the Status Affect, something that commonly happened in games. It happened in real life too, only in games the affects were immediate.