The number of people taking illegal drugs worldwide rose last year by about 15 million to 200 million, the UN annual drugs report says.
Afghanistan remains the world's major opium producer
The value of the global drugs trade, which the report says is about $320bn, is higher than the gross domestic product of 90% of the world's nations.
It also says Afghanistan produced 87% of the world's illegal supplies of opium last year.
Cocaine production fell in Colombia, but rose in Peru and Bolivia.
"This is a worrying loss of momentum for both countries, which had already made significant progress to curb coca production," the report said.
DRUG USERS AROUND THE WORLD
160m use cannabis
14m use cocaine
16m use opiates
Of those, more than 10.5m use heroin
The report said there was a long-term trend towards rising opium production in Afghanistan - although this had been offset by strong declines in Burma and Laos.
It added that there were positive signs for Afghanistan, where in 2005 the area under poppy cultivation had fallen from record levels last year.
The report said the Afghan government was strengthening its control over the economy, following elections in 2004.
Cannabis is the most widely used drug, and is taken by 160 million people, the report said.
Cocaine abuse, it said, was declining in North America, but rising in Europe.
The report said there were an estimated 14 million cocaine users worldwide, two-thirds of them in the Americas.
Around 16 million people use opiates - including 10.5 million taking heroin.