Decriminalizing drug possession and providing users with treatment rather than jail time helped cut teen drug use and the number of people seeking treatment doubled in Portugal, according to a new study from the libertarian Cato Institute.

Time magazine reported April 26 that Portugal decriminalized all drugs, including cocaine and heroin, in 2001. Instead of jail, people found in possession of drugs are sent to an assessment panel that can recommend -- but not require -- that they get addiction treatment.

Despite fear that the law would make Portugal a magnet for drug tourism, the Cato study found that youth drug use declined in the five years after decriminalization took effect, treatment referrals doubled, and the rate of HIV caused by sharing needles declined. Portugal now has the lowest rate of lifetime drug use among people over age 15 -- 10 percent -- in the European Union, compared to 39.8 percent among U.S. residents ages 12 and over.

Between 2001 and 2006, lifetime use of illicit drugs declined from 14.1 percent to 10.6 percent among 7th- to 9th-graders in Portugal.

"Judging by every metric, decriminalization in Portugal has been a resounding success," said Cato researcher Glenn Greenwald. "It has enabled the Portuguese government to manage and control the drug problem far better than virtually every other Western country does."

"I think we can learn that we should stop being reflexively opposed when someone else does [decriminalize] and should take seriously the possibility that anti-user enforcement isn't having much influence on our drug consumption," added Mark Kleiman, a drug-policy expert at UCLA,

However, Kleiman stressed that Portugal's size and cultural differences make it a poor model for the U.S., and fellow expert Peter Reuter of the University of Maryland said the trends reported in Portugal could be cyclical and not necessarily related to decriminalization.