Drug use is moving away from cocaine and opiates and towards synthetic drugs such as amphetamines, the UN says.
In its World Drug Report it says it expects that soon there will be more people using synthetic drugs than opium, heroin and cocaine together.
The UN Office on Drugs and Crime (UNODC) also found that cocaine consumption has fallen significantly in the US in recent years.
But the number of cocaine users in Europe has doubled, it says.
The shift in demand has led to South American drug cartels establishing new routes through West Africa.
Trafficking is causing instability in many developing countries, particularly in Africa and Latin America, the report says.
"People snorting coke in Europe are killing the pristine forests of the Andean countries and corrupting governments in West Africa", UNODC director Antonio Maria Costa said.
