VIENNA, June 26 (Reuters) - A fresh blight is poised to hit Afghanistan's poppy fields this year, driving up opium prices and threatening to fuel a shift to potentially lethal heroin substitutes like "krokodil", the U.N. drugs watchdog said on Tuesday.
Plant diseases destroyed nearly half the 2010 opium harvest in Afghanistan, the world's biggest producer, but output there rebounded 61 percent last year, the U.N. Office on Drugs and Crime (UNODC) said in its 2012 World Drug Report.
That helped put global opium production at 7,000 tonnes in 2011, still more than a fifth below the 2007 peak.
"We may anticipate that this year there will be another plant disease - maybe not to the same scale as 2010 - but (it) still may affect, especially in the southern part of Afghanistan, poppy cultivation," UNODC Executive Director Yuri Fedotov said.
"This means that the production of opium may not increase or may even decrease, but at the same time definitely it would lead to an increase in prices for the next year. That is something we need to address very seriously."
The UNODC report cited indications that shortages had encouraged users in some countries to replace heroin with other substances such as desomorphine - whose street name is krokodil - acetylated opium, and synthetic narcotics.
Krokodil is a crude, codeine-based drug that users inject, risking serious health problems as it attacks body tissue.
"It is a powerful drug which can kill people in just two months, in a few weeks," Fedotov said.
It was hard to gauge what impact the 2010 crop failure in Afghanistan had on major markets, the report said, but drug seizures fell in most countries getting Afghan opiates. Some European countries, including Britain and Russia, saw heroin droughts.
Opiate prices in Europe and the Americas had not changed much since 2009, officials said, but farm-gate prices in Afghanistan and number-two producer Myanmar kept rising in 2010 and 2011. A kilo of opium costs around $200-$250 in Afghanistan.
Rising prices at times of increasing output could reflect under-reported demand from Asia and Africa, a growing market for raw opium not made into heroin, a parallel market for morphine or speculation on local markets, the report said.
Drug syndicates also tended to stockpile opium to be able to smooth out supply fluctuations, UNODC officials said.
The 2012 report showed overall use of illicit drugs seems to have stabilised but was on the rise in several developing countries, especially those along trafficking routes.
Fedotov cited as an example growing consumption of cocaine in West Africa, now a transit route for shipping Latin American supplies to Europe, increasingly from Bolivia and Peru as output in Colombia - mainly bound for North America - declines.
Cannabis remained the world's most popular illicit drug, with between 119 million and 224 million established users worldwide, the report said.
That was followed by amphetamine-type stimulants (ATS), the use of which was largely stable, although methamphetamine and ecstasy appeared to be on the rise.
Seizures of methamphetamine more than doubled in 2010 from 2008 due to big hauls in central America and Asia. Ecstasy pill seizures more than doubled in Europe from 2009 to 2010, and the drug's use seemed to be rising in the United States and Oceania.
The report stressed the health and security threats illicit drugs posed, renewing UNODC's call for an integrated approach to reducing both supply and demand.
"Heroin, cocaine and other drugs continue to kill around 200,000 people a year, shattering families and bringing misery to thousands of other people, insecurity and the spread of HIV," Fedotov said.
Around 230 million people, roughly five percent of the world's adult population, are estimated to have used an illicit drug at least once in 2010. Around 27 million, or 0.6 percent of adults, are problem drug users, mainly of heroin and cocaine.
By contrast, surveys have shown 42 percent of adults drink alcohol and a quarter use tobacco.
Fedotov said his agency was looking into reports that Uruguay's government planned to legalise the marijuana market as part of a drive to stop rising crime.
"If these reports are confirmed, of course it will be a disappointing development," he told reporters, citing international conventions against such a step.
"Cannabis is not so innocent as some people prefer to describe (it)," he said, noting its users faced irreversible physiological changes and often moved on to harder drugs. (Reporting by Michael Shields; Editing by Nick Macfie)