Opium poppy cultivation worldwide was down 22 percent in 2005, a United Nations report said Monday, part of a generally favorable, albeit inconclusive, trend in efforts by governments to contain illicit drug production.

The U.N.'s 2006 World Drug Report also found that cocaine use is reaching alarming levels in Western Europe. Consumption of marijuana, the most widely used illicit drug, continued to increase, the study said.

It attributed the decline in opium poppy cultivation to cutbacks in the three main source countries of illicit opium: Afghanistan, Myanmar and Laos. Opium is the main ingredient for heroin.

"In Afghanistan, in 2005, opium poppy cultivation decreased for the first time since 2001," the report said. Still, it said, that country accounted for 89 percent of opium production worldwide.

The State Department's annual report on illicit drugs, issued in March, acknowledged that opium production is hampering democracy-building efforts in Afghanistan.

"Afghanistan's huge drug trade severely impacts efforts to rebuild the economy, develop a strong democratic government based on rule of law, and threatens regional stability," the State Department report said.

Despite the sharp decrease in the total area under cultivation in all opium-producing countries, the U.N. report said production was down only 5 percent due to more favorable weather conditions during the 2005 growing season in Afghanistan.

"The world's supply of opium has shrunk, but in an unbalanced way," the study said. "Within a few years, Asia's notorious Golden Triangle, once the world's narcotics epicenter, could become opium-free. But in Afghanistan, while the area under opium cultivation decreased in 2005, the country's drug situation remains vulnerable to reversal. This could happen as early as 2006."

Assessing the gamut of illicit drugs, from heroin and cocaine to ecstasy, amphetamines and marijuana, the report concluded, "Drug control is working and the world drug problem is being contained."

Levels of drug cultivation and drug addiction are much lower than they were 100 years ago, it said.

"Even more importantly, in the past few years, worldwide efforts to reduce the threat posed by illicit drugs have effectively reversed a quarter-century-long rise in drug abuse that, if left unchecked, could have become a global pandemic," the report added.

On coca, the plant used to make cocaine, the report reaffirmed a Bush administration finding in April that that total area of coca cultivation in Colombia has been increasing despite sustained, U.S.-backed eradication efforts since 2000.

The administration says the $4 billion invested in its anti-cocaine strategy in Colombia is working, but some members of Congress and independent experts disagree.

Colombia accounts for 54 percent of coca cultivation globally, followed by Peru (30 percent) and Bolivia (16 percent), according to the study.

Most cocaine continues to be used in the Americas, particularly North America, which accounts, with 6.5 million users, for almost half the global cocaine market, the report said.

While use in the Americas declined, the report said, it is rising in Europe, where the estimated 3.5 million users account for 26 percent of the worldwide total, the largest concentration of which is in West and Central Europe.

Cocaine use in those regions (1.1 percent) is only about half the figure in North America, the report said, but the trend is pointing upward.

Annual "prevalence rates" of more than 2 percent, it said, have been reported from Spain and the United Kingdom.