"We've never really seen it on the street like we've seen cocaine and heroin," Riley said. He worries that if the estimated 180,000 members of street gangs in Chicago get involved in meth trafficking, violence could follow.
Like the U.S., Mexico has tightened laws and regulations on pseudoephedrine, though some labs still are able to obtain large amounts from China and India. To fill the void, cartel chemists have turned to an old recipe known as P2P that first appeared in the 1960s and 1970s in some parts of the western U.S.
That recipe uses the organic compound phenylacetone. Because of its use in meth, the U.S. government made it a controlled substance in 1980, essentially stopping that form of meth in the U.S. But in Mexico, the cartels can get phenylacetone from other countries, DEA experts said.
In the third quarter of 2011, 85 percent of lab samples taken from U.S. meth seizures came from the P2P process — up from 50 percent a little more than a year earlier, DEA spokesman Rusty Payne said.
Federal agents say the influx of meth from Mexico illustrates the difficulty of waging a two-front war on the drug in neighboring countries. When one source of the drug is dealt a setback, other suppliers step in to satisfy relentless demand.
Considering the relatively untapped market of bigger American cities, the rise of Mexican meth is not surprising, said Illinois State University criminologist Ralph Weisheit, a meth expert.
"It's something that was inevitable," Weisheit said. "This wasn't hard to predict."
American authorities are not the only ones taking notice. The sharp spike in meth activity also is evident from the other side of the border. Seizures of labs and chemicals have increased nearly 1,000 percent in the past two years.
Last year, Mexican authorities made two major busts in the quiet central state of Queretaro, seizing nearly 500 tons of precursor chemicals and 3.4 tons of pure meth with a street value of more than $100 million. In Sinaloa, investigators found a sophisticated underground lab equipped with an elevator and ventilation systems as well as cooking and sleeping facilities. The facility was reachable only by a nearly 100-foot tunnel with its opening concealed under a tractor shed.
And in February, soldiers in western Mexico made a historic seizure: 15 tons of pure methamphetamine, a haul that could have supplied 13 million doses worth more than $4 billion.
The meth problem is spilling into other parts of Latin America too. In December and January, Mexican authorities seized nearly 900 tons of precursor chemicals at Mexican ports, almost all of it bound for Guatemala, which seized about 1,600 tons of meth precursors in 2011 — four times the 400 tons seized there a year earlier.
For now, cocaine remains far and away the cartels' most profitable drug. The RAND Corp. estimates the annual street value of cocaine is about $30 billion, heroin about $20 billion and meth about $5 billion.
But cocaine is getting more expensive and less pure. According to the DEA, the price per pure gram of cocaine rose 59 percent from 2007 through September 2011. At the same time, the purity level dropped 25 percent.
Cocaine also typically comes from Colombia, meaning Mexican cartels serve as middle men who compete against each other to smuggle it into the U.S. That marginalizes their profits.
Because methamphetamine is a synthetic drug the cartels can make for themselves, the profit potential is enormous.
"It's not plant-based," Weisheit said. "It can be completely produced in Mexico. It's very compact, and that makes it easy to smuggle."
Associated Press writers Mark Stevenson in Mexico City and Christopher Sherman in McAllen, Texas, contributed to this report.
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