NFL players are being warned about consuming meat produced in China and Mexico that potentially contains clenbuterol, which is banned under the league's performance-enhancing substance policy.
The drug-testing program's independent administrator sent a memo to players, saying "consuming large quantities of meat while visiting those particular countries may result in a positive test."
Clenbuterol is a muscle-building and weight-loss stimulant.
"Players are warned to be aware of this issue when traveling to Mexico and China," the memo read. "Please take caution if you decide to consume meat, and understand that you do so at your own risk."
The drug-testing program again advised: "Players are responsible for what is in their bodies."
The Oakland Raiders will face the Houston Texans on Monday Night Football on Nov. 21 in Mexico City as part of the league's international series. The Raiders also hosted a fan fest as part of the NFL draft this past Saturday in Mexico City.
Texans left tackle Duane Brown tested positive for clenbuterol last season after a bye-week trip to Mexico, during which he ate Mexican beef, sources told ESPN.
After a months-long process, Brown was finally cleared in April, sources said, allowing him to avoid what would have been a 10-game suspension. His case serves as a cautionary tale for other players.
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Such culinary concerns aren't restricted to the NFL.
In 2011, five players on Mexico's national soccer team tested positive for clenbuterol, and the country's federation ruled the positive tests were caused by contaminated meat.
At the 2011 U-17 World Cup held in Mexico, FIFA found a majority of all players tested had traces of clenbuterol in their systems.
Mexican cattle ranchers are banned from using clenbuterol as a growth enhancer, but reports suggest that it is still used widely.
Information from ESPN.com's Tania Ganguli and Dan Graziano contributed to this report.