American distance runner Fernando Cabada has become the latest athlete to be cleared of a clenbuterol doping offence after claiming to have consumed contaminated meat.
Cabada, a marathon specialist who competed at the 2007 World Championships in Osaka, failed an out of competition test for the banned steroid in December.
However, the 34-year-old was successfully able to argue that he must have digested the substance inadvertently while training in Mexico.
"Consistent with numerous prior reported cases globally, the issue of illicit administration of clenbuterol to animals destined for food production can result in, under specific conditions, a positive sample from an athlete," a United States Anti-Doping Agency (USADA) statement said.
"WADA has issued specific warnings about this problem in China and Mexico.
"During its investigation into the circumstances that led to the positive test, USADA gathered evidence from Cabada and reviewed Cabada’s whereabouts, dietary habits, and the laboratory reports demonstrating very low parts per billion concentrations of the prohibited substance in the athlete’s urine sample.
"USADA concluded that it was highly unlikely that the presence of clenbuterol in the athlete’s sample resulted from a source other than clenbuterol contaminated meat consumed in Mexico.
"As a result, Cabada will not face a period of ineligibility for his positive test, and because the sample was collected out-of-competition, there are no competitive results to be disqualified."
Cabada boasts a marathon personal best of 2 hours 11min 36sec and also finished 46th at the World Half Marathon Championships in Copenhagen.
Clenbuterol-contaminated meat cases have been most common in China and Mexico, with 109 footballers thought to have tested positive for it when playing in the 2011 Under-17 World Cup in Mexico.
The most notable failure for the substance 2010 when Spanish cyclist Alberto Contador was stripped of his 2010 Tour de France and 2011 Giro d'Italia titles after such a failure.
But the Court of Arbitration for Sport did subsequently rule that "accidental ingestion" was to blame.
However, contaminated meat cases are far less prevalent in other parts of the world.
USADA added that such a case has never been proved in the US.