AAS stimulate erythropoiesis (RBC production) which is great for training and the crazy pumps but having too many RBCs can increase the viscosity of the blood. Blood that is too thick can be very dangerous. That's why people can die from blood doping. Your buddy at the very least should take some aspirin ED and maybe even have a glass of wine at night, these both help to thin the blood, lessening the risk of clotting. Tell him not to take this lightly.