The risk then is largely to Mexican consumers, and anyone who visits the country and consumes steady amounts of beef. In April, Germany's anti-doping agency warned traveling athletes not to eat meat in Mexico because it might result in positive doping results.
The economic incentive for ranchers to use illegal steroids is great.
"A steer normally yields 55 percent meat. But a steer fed clenbuterol yields 62 to 65 percent," said Martinez, who operates the Martin Butcher at a central Celaya market. He pulled out a calculator and showed how using the steroid for a month or two before slaughter can bring in an additional 100 pounds or more of beef for each steer.
The problem, he added, is that "a few ranchers overdo it with the dosage."
"The use of this substance to fatten cattle is common," financial journalist Enrique Campos Suarez wrote in the newspaper El Economista, adding that it got the moniker "cattle cocaine" because of the "enormous profits that are said to be earned in the industry by those who sell it."
Since 2007, Mexican law penalizes ranchers who use banned steroids in cattle with potential jail terms of seven years. But the law is widely disregarded.
Just five weeks ago in Aguascalientes, authorities confiscated a ton of beef liver after five people were hospitalized there. Two weeks ago, officials took control of 850 head of cattle in Jalisco state after finding feed spiked with clenbuterol at the La Estrella ranch.
Martinez, who heads an association of 170 butchers in Celaya, said meat vendors occasionally had discussed not selling steroid-tainted beef. But there are always holdouts, and bribes reach into the local health departments, which look the other way.
"I agree that you should get rid of clenbuterol. But it has to be everyone, not just a few," Martinez said.
Even as the office of Health Secretary Jose Angel Cordova denied there was a problem with Mexican beef, the secretary acknowledged that butchers and consumers had grown accustomed to the less fatty look of meat raised on clenbuterol.
"Because it has a better appearance, some butchers prefer this meat and don't realize they are committing a crime," Cordova said, according to the semiofficial news agency Notimex.
Those sickened by tainted meat are usually those who buy organ meat, mainly liver, at markets and cook it at home, said Joel Manrique Moreno, the director of sanitary risk protection for Guanajuato state.
"An hour later, they have the symptoms," he said, which can include "headache, palpitations, nervousness and fluctuating blood pressure rates."
Manrique said poisoning these days was "exceedingly rare," an assertion refuted by a veterinarian and former federal legislator, Ernesto Davila Aranda.
"This state is swimming in clenbuterol. They are poisoning people, and the authorities aren't doing anything about it," Davila told the Guanajuato a.m. newspaper last month.
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