DAVID W. KOOP, Associated Press Writer

MEXICO CITY -- Mexican cartels are increasingly going "old school" to keep supplying America with methamphetamine despite an ingredient squeeze.

Some gangs have responded to a Mexican crackdown on their meth chemical of choice — pseudoephedrine — by reviving a production method so old, it was used by U.S. motorcycle gangs and bathtub chemists in the 1970s and '80s, recent seizures show.

The re-emergence of the "P2P method" demonstrates how frustrating it is to crack down on a synthetic drug that — unlike cocaine, heroin and marijuana — comes from recipes of chemical ingredients, known as "precursors," instead of a plant.

When police succeed in cutting off the supply of one precursor, traffickers move on to or make another.

"Chemical restrictions are like squeezing mud, the stuff just comes out between your fingers," said Steve Preisler, who wrote the "Secrets of Methamphetamine Manufacture" under the nom de plume Uncle Fester and is considered the father of modern meth-making. "They make life difficult for the smurfers (home producers) but for people with connections, well, they find it to be no problem at all."

Still, authorities contend going after precursors has produced results. The crackdown contributed to a sharp decrease in meth production in Mexico and a drop in availability on U.S. streets in 2007 and in the first half of 2008, according to the U.S. National Drug Intelligence Center's 2009 methamphetamine report.

And authorities say the P2P method is less desirable for the gangs because it reputedly produces a less-potent drug.

But using easy-to-get phenylacetic acid, as well as new sources of contraband pseudoephedrine, Mexico's meth gangs regrouped, and their output was stabilizing or increasing by late 2008, the drug center's assessment said.

The latest turn in the meth fight began in 2005, when Mexican officials started imposing progressively tighter restrictions on imports of the ephedrine and pseudoephedrine used in cartels' meth labs. A near-total ban on medicines containing pseudoephedrine went into effect last year.

Traffickers found ways to smuggle the banned chemical into Mexico, and they moved some manufacturing abroad. They also started looking into new ingredients.

They came across phenyl-2-propanone, or P2P. While P2P itself is highly restricted and closely monitored by authorities, there are many ways to make it. Gangs found they could get their hands on phenylacetic acid, which can be made into P2P, which in turn can be made into meth. They began acquiring phenylacetic acid and its derivatives in huge quantities.

DEA tests of confiscated methamphetamine from Mexico show that in 2007 only 1 percent of meth was made using phenylacetic acid and related chemicals. So far this year, it is 16 percent.

In October, Mexican officials announced the record seizure of 37 tons of phenylacetic acid derivatives — sodium phenylacetate and 2-phenylacetamide — that could have made up to 25 tons of crystal meth.

The announcement of the coordinated seizures in the border city of Nuevo Laredo and in the Pacific port of Manzanillo also revealed earlier big hauls of phenylacetic acid: 15 tons in May, almost 2 tons in March and 1.8 tons in June and July.

"We are starting to see a rise in chemicals that are easier to get," said U.S. Drug Enforcement Administration spokeswoman Dawn Dearden.

Preisler, who works at an electroplating factory and has been arrested twice in the U.S. for his work with methamphetamine, says he isn't surprised traffickers have turned to P2P.

"P2P is old school," he said. "Hell, I used to cook by that route circa 1980."

The fight has come full circle. In the 1980s, the U.S. government severely restricted access to P2P seeking to curtail methamphetamine production. Meth makers shifted to ephedrine, which could be found in common cold remedies. When authorities cracked down on ephedrine, they switched to pseudoephedrine, the active ingredient in Sudafed and other decongestants.

When U.S. authorities regulated bulk sales of the ephedrines, meth production shifted to Mexico, where, at the time, gangs could get their hands on mammoth quantities of pseudoephedrine imported from China and India.

Mexico was soon supplying up to 80 percent of the drug sold in the U.S., and American authorities were calling meth the No. 2 drug threat to society after cocaine.

Once Mexico restricted imports and sales of pseudoephedrine, the cartels took a hit.

The volume of methamphetamine seized in the United States fell 34 percent, from 7.1 tons in 2006 to 4.7 tons in 2007, according to the U.S. National Drug Intelligence Center. It also said it observed decreased drug purity. Dearden says DEA agents found the price of meth increased.

Experts say a crackdown on phenylacetic acid would likely just push traffickers to other chemicals.

"People forget that these are synthetically made drugs, and we haven't even seen the end of all the possible recipes," said Ralph A. Weisheit, an Illinois State University professor who wrote "Methamphetamine: Its History, Pharmacology and Treatment."