The annual snapshot of drug use says about 230 million people, one in every 20, took illicit drugs at least once in 2010. There are about 27 million problem drug users, mainly chronic heroin or cocaine users, representing about 0.6 per cent of the world's population.

The UN says production of opium soared by 61 per cent in Afghanistan from 3600 tonnes in 2010, when plant disease wiped out almost half the crop yields and triggered steep price rises, to 5800 tonnes in 2011. Global opium production reached 7000 tonnes in 2011. Heroin use in North America and Europe appears to be stable or shrinking. The UN says that in Africa and Asia, which now account for 70 per cent of heroin users, there is a clear lack of data but it is possible there is increasing but undetected patterns of use.

It also confirms the sharp decline in cocaine production, with an 18 per cent drop in the total area under coca bush cultivation since 2007 with the steepest decline in Colombia. This has been accompanied by a significant fall in cocaine consumption in North America. In Europe, cocaine use remains stable but continues to rival use in the US and Canada.

However, the decline in heroin and cocaine has been matched by rising levels of synthetic drugs production, including the production of ''legal highs'', which are synthesised in laboratories to imitate the effects of more traditional drugs.

The UN report also confirms the rise of the non-medical use of prescription drugs, especially in Australia and the US, where their consumption is now more widespread than any other illicit substance, apart from cannabis.