Production of the raw material for cocaine in the Andes region of Latin America has fallen by 20% since 1998, according to the United nations.
The UN says demand for cocaine is growing in some parts
The UN Office for Drugs and Crime said coca production in Colombia, Peru and Bolivia had reached its lowest point in 14 years thanks to anti-drug campaigns.
The three countries are the world's main producers of coca.
The UNODC's director warned the trend could only continue if farmers were offered other ways of making a living.
"The importance of a steady decline of coca cultivation in the Andean region cannot be overestimated," said Antonio Maria Costa.
He noted that Coca cultivation dropped 11% in 2003 in the three countries overall to 153,800 hectares (380,000 acres):
Colombia saw its crop cultivation area fall 16% to 86,000 hectares (212,000 acres), its lowest levels since 1997
Peru's production dropped 5% to 44,200 hectares
Bolivia's output was recorded as 23,600 (58,000 acres)
However, Mr Costa also warned of worrying new trends in illegal drugs.
- an increased consumer preference for synthetic instead of planted drugs
a rise in cocaine consumption in Europe
new planting techniques by coca farmers to avoid aerial spraying
The UN compiled its data on the illegal Andean crops using satellite
imagery and aerial photos, verified on the ground.