In sports, oping refers to the use of performance-enhancing drugs, particularly those forbidden by organizations that regulate competitions. Doping is mostly done to improve athletic performance. This is why many sports ban the use of performance enhancing drugs. Another form of doping is blood doping, either by blood transfusion or use of the hormone erythropoietin (EPO) or anabolic steroid Tetrahydrogestrinone (THG). Also considered "doping" by many is the use of substances that mask other forms of doping. Doping is considered unethical by most international sports organizations and especially the International Olympic Committee. The reasons are mainly the health threat of performance-enhancing drugs, the equality of opportunity of the athletes and the exemplary effect of "clean" (doping-free) sports in the public.