In sports,<unk> refers to the use of performance-enhancing drugs, particularly those that are forbidden by the organizations that regulate competitions.  Another form of<unk> is blood<unk>  either by blood transfusion or use of the hormone erythropoietin (EPO).  Also considered<unk> " by many is the use of substances that mask other forms of<unk> [citation needed]<unk> is considered to be 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" <unk> free) sports in the public.
Currently, tetrahydrogestrinone (THG) and modafinil are causing controversy throughout the sporting world, with many high profile cases attracting major press coverage as prominent United States athletes have tested positive for these<unk> substances. Some athletes who were found to have used modafinil protested as the drug was not on the prohibited list at the time of their offence; however, the World Anti-Doping Agency (WADA) maintains it is a substance related to those already banned, so the decisions stand. Modafinil was added to the list of prohibited substances on August 3, 2004, ten days before the start of the 2004 Summer Olympics.
In recent years, gene<unk> has been reported as being an emerging form of<unk>  Gene<unk> would be very difficult to detect as well as permanent and irreversible.
Sports lawyer Michelle Gallen has said that the pursuit of<unk> athletes has turned into a modern day witch hunt.
Doping 
Addiction
Rational addiction
Withdrawal
Annoyance
Fetishism
Adaptive behavior
Information addiction