Five Mexican players who tested positive for clenbuterol before the Gold Cup in June will face no further action after FIFA determined the tests were caused by contaminated meat.
The World Anti-Doping Agency said Wednesday it had dropped its appeal at the Court of Arbitration for Sport, where it planned to challenge a Mexico Football Federation decision clearing the players of doping.
WADA says it accepted FIFA's "compelling evidence" from the recent Under-17 World Cup in Mexico that the country has a "serious health problem" with meat contaminated with clenbuterol.
"WADA applauds FIFA for the further research it has initiated," the anti-doping watchdog said in a statement.
FIFA gathered the evidence while working with the government of Mexico.
"The studies conducted by FIFA showed the correctness of the footballers' claim that the positive samples were the result of meat they had ingested at a training camp ahead of the tournament," the governing body of world football said.
Mexico won the Gold Cup despite the absence of goalkeeper Guillermo Ochoa, defenders Edgar Duenas and Francisco Rodriguez, and midfielders Antonio Naelson and Christian Bermudez. It beat the United States 4-2 in the final in June.
WADA said Mexico's government has agreed to help tackle the issue of farmers giving steroids to livestock, which is illegal there.
"Already several arrests have been made pursuant to these laws and large amounts of clenbuterol seized. Investigations are to continue," WADA said.
WADA issued a warning to athletes travelling to Mexico to compete at the two-week Pan American Games which open Friday in Guadalajara.
"If possible, they should eat in cafeterias designated as safe by event organizers and also try to eat in large numbers," WADA advised. "The state government in Guadalajara has taken steps to ensure the meat available to athletes at the Pan American Games will not be contaminated."
The Mexican case is the second time this year that WADA has dropped an appeal after an athlete used a defence of contaminated meat to explain consuming clenbuterol.
German table tennis player Dimitrij Ovtcharov tested positive after competing in China, which also has long-standing issues with illegally feeding steroids to livestock.
Three-time Tour de France winner Alberto Contador will use the same argument as part of his defence at CAS next month.
WADA and the International Cycling Union appealed to the sports court after a Spanish cycling federation tribunal accepted Contador's explanation that he inadvertently ate a contaminated steak during his 2010 Tour victory.
Contador's scheduled four-day hearing opens Nov. 21.