Milk of the poppy is used as a pain killer or anesthetic in the Known World. It is normally given to those mortally wounded or in great pain. It has a quick effect of causing sleep, even for people in great pain.[3][4][5] During this sleep, people often have strange "poppy dreams".[5][6][7][8] Milk of the poppy also has an incapacitating effect, "filling your head with clouds",[9] even after the user has woken from sleep.[6] Because of this, and possibly because it is also addictive or because overuse causes tolerance,[10] some prefer to go through strong pain instead of consuming it.[5][11][12][8] Overuse of milk of the poppy may make the user's face become puffy.