Legal prescription drugs are being trafficked illegally over the internet, the UN's anti-drugs body has warned.
Hundreds of millions of dollars worth of legal drugs move illegally
Each year, 10 million illegal shipments of prescription drugs enter the US - where prescription drug abuse now rivals the abuse of all illegal drugs.
Canada and Mexico suffer the same problem, the International Narcotics Control Board (INCB) said.
And drug crop replacement schemes have not been very effective, it says, adding alternative measures are needed.
In other findings:
- More than 34 million people in Africa and 30 million people in the European Union use marijuana
- Cocaine production and illegal drug trafficking is on the rise in South America, and illegal coca bush growing has increased in Bolivia and Peru
- Injecting drugs is leading to higher HIV/Aids rates in South Asia, especially in India and Nepal
- Afghanistan produces about 87% of the world's opium.
Legal prescription drugs are being trafficked illegally over the internet, the Vienna-based INCB warned in its annual report.
It said hundreds of millions of US dollars worth of drugs such as painkillers and inhalants - some stronger than morphine - were being shipped without prescriptions.
It is much more complex than initially anticipated to halt the illicit cultivation of [drug] crops
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Users came from "all age groups, including schoolchildren", the report said.
"The sale of controlled drugs from illegally operating internet pharmacies" was part of the problem, the report said.
Governments must do more to fight the smuggling of illegal drugs by post, it urged.
INCB President Hamid Ghodse said he feared the trend could develop in other parts of the world as well.
The INCB report added that nearly 8% of all Americans aged 12 and above were using illegal drugs such as cocaine, heroin and marijuana.
The report also said programmes in developing nations to replace illegal drug crops - particularly opium poppies and coca leaves - with legal crops had not been working well.
Afghanistan remains the world's top illicit opium producer
The schemes should be rethought and extended beyond rural communities to cities "mired in the drug problem", Mr Ghodse said.
However, the report acknowledged that most countries implementing replacement schemes had seen a drop in the growth of illicit crops.
In Laos, the total area under opium poppy cultivation dropped by 75% from 1998 to 2004. In Colombia, the total area on which illicit coca bush cultivation took place decreased by more than 50% from 2000 to 2004.
The report also urged governments around the world to screen all routes of incoming and outgoing international mail.
It recommended limiting the number of entry points for parcels, to control consignments more effectively.
The report also highlighted the rapid increase in the use of the highly addictive synthetic drug methamphetamine, also known as crystal meth.