Mexico recently took a dramatic step in the war on drugs, decriminalizing possession of small amounts of marijuana, cocaine and heroin. In the midst of battling the drug cartels that grow fat on the profits of drug abuse and addiction, not to mention all of the violent crime that accompanies drug trafficking, the Mexican Government has sent a clear message. Unfortunately, it’s the wrong message. It is the message of surrender.

Mexican officials say the move will allow their law enforcement agencies to focus on fighting the big cartels, rather than small abusers. Predictably, drug legalization advocates cheered the move.

But other nations’ experiences with legalization have shown that these schemes rarely deliver on what they promise, while bringing with them significant new problems. Indeed it seems counter-productive in the extreme to be launching the nation’s most aggressive fight against the narcotraffickers while at the same time giving a wink and nod to drug use at home. It as if Mexico were trying to develop a stronger market for drug use at home.

The Mexican Government says that the new law is meant to allow law enforcement to focus on the major trafficking of drugs and not waste resources on small-time users. As the United States Government does with U.S. Drug Enforcement Administration (DEA), Mexico can focus its national resources on major traffickers without making a public proclamation that using drugs is okay.

When I headed the DEA in the early part of this decade, I toured a pilot legalization project in south London, where a local police commander launched an experimental program to de-emphasize small-time drug arrests. In the Lambeth borough, where the project was attempted, I saw drug dealers openly pushing hard drugs like heroin and crack. Residents of the working class neighborhood reported open drug use—indeed, I witnessed a young couple injecting heroin in an abandoned building—and significant increases in crime.

Legalization has even been tried in the United States, although most Americans may not realize it. In 1975, the Supreme Court of Alaska ruled that it was constitutional for adults to possess small amounts of marijuana for home consumption. The results were predictable enough: Drug use skyrocketed. A 1988 University of Alaska survey showed that the state’s teenagers used marijuana at a rate more than twice the national average for their age group. The report also showed a frequency of marijuana use that suggested it wasn’t experimental but was a well-incorporated practice for teens. Fed up with this dangerous experiment, Alaska’s residents voted in 1990 to recriminalize the possession of marijuana. A ballot proposal to legalize marijuana possession in Alaska in 2004 was also soundly defeated.

It’s also important to point out that legalizing (or “decriminalizing”) drug use won’t change the violent fight the Mexican Government is facing in going after criminal organizations trafficking drugs. It is still illegal to move distribute large quantities of drugs in Mexico, just as it is in the United States. But this is where the money is. The cartels will continue to bribe, kill and steal as necessary to traffick major shipments of drugs.

Some have suggested that we should therefore abandon the entire war on drugs. I disagree. It’s one of the great myths of our era that U.S. anti-drug efforts have not made a difference. Overall drug use in the United States is down from the levels of the 1970s, thanks to tough enforcement coupleed with effective drug education programs and drug treatment programs. In fact, while the use of illicit drugs has fluctuated over the years, the overall trend over the last three decades has been toward decreased usage. (To take the most recent good news, the 2008 National Survey on Drug Use and Health, released just last week, shows that youth drug use has shown a significant drop since 2002.)

It’s important to note that this progress did not come from decriminalization or legalization. It stems from a program that integrates enforcement with innovative approaches like drug courts, drug testing in the workplace, community coalitions to fight drugs and enhanced investment in education and prevention. That’s the formula for reducing drug abuse and addiction. That’s the formula for saving lives.

The precedents are clear: Where legalization has been attempted, regrets soon followed as the costs became clear. I fear our neighbors to the south will soon relearn this tragic lesson.