Since the vote by Congress last week, lawmakers have said they are unsure who amended the bill, originally aimed at legalizing possession of small quantities of drugs among addicts, to make it apply to all "consumers."
The Bush administration is refraining from public criticism of Mexico. But in private meetings Monday with Mexican officials in Washington, U.S. officials tried to discourage passage of the law, U.S. Embassy officials here said.
"Any country that embarks on policies that encourage drug use will get more drug use and more drug addiction," said Tom Riley, a spokesman for the White House Office of National Drug Control Policy.
"Many countries, including the U.S. and Mexico, see the drug problem as a trafficking problem," he said. "But the real problem isn't trafficking, it's drug use. The costs of drug addiction are staggering."
Mexico has for years blamed Americans for fueling the multibillion-dollar illegal drug trade with their $10, $50 and $100 drug purchases. One cartoon here showed Uncle Sam kneeling over a map of the United States and Mexico, snorting a giant line of cocaine piled along the border.
News of the pending Mexican law spread quickly over the Internet, reaching the website of High Times, a glossy monthly magazine that features photo spreads of marijuana from around the world.
"I know I'll be booking my trip as soon as I hear the OK!" wrote "Beefy" to general agreement among his cyber peers.
Drug use by Mexicans grew as smugglers began receiving payments in drugs rather than cash from Colombian suppliers, experts say. The drug surplus triggered more local sales and use.
"There's been a big increase in addiction in recent years," said Mago Marchina of Clinica Nuevo Ser, a Tijuana drug treatment center.
Reliable figures on how many Mexicans are addicted to drugs are hard to come by, but Mexico's National Council Against Addictions has said that more than half of addicts use cocaine, and a third report hard-core marijuana use.
A growing war among rival drug gangs in Mexico -- primarily the so-called Gulf and Sinaloa cartels -- has ushered in a new era of brutality, with torture routine and bodies burned and dismembered.
More than 1,000 people have been killed in the last 18 months in fighting over smuggling routes to the United States, mostly in border cities, Acapulco and the capital. Automatic weapons and explosives are common tools; police and journalists are increasingly frequent targets.
