Cheats were warned Thursday that they are putting themselves in serious danger by taking a "toxic" drug which was forced on to the black market after it was withdrawn by its manufacturer.
The World Anti-Doping Agency (WADA) issued the warning over the substance, identified only as GW501516 which is being sold to and used by some athletes.
"It has come to WADA's attention that the black market substance GW501516 is being sold to and used by some athletes," said a WADA statement.
"The side effect of this chemical compound is so serious that WADA is taking the rare step of warning 'cheats' to ensure that there is complete awareness of the possible health risks to athletes who succumb to the temptation of using GW501516 for performance enhancement."
WADA added that the developmental drug was withdrawn from research by the pharmaceutical company and terminated when serious toxicities were discovered in pre-clinical studies.
"Clinical approval has not, and will not be given for this substance," said the body.
"However, GW501516 has been available for some months on the black market, through the Internet and elsewhere. Anti-Doping authorities have already seen its use by athletes, as there are a number of positive cases."