RARE good news in the bloody fight against narcotics gave drug warriors in the Americas reason to boast on June 22nd. First, Jamaican police arrested Christopher “Dudus” Coke, a gang leader wanted in the United States. The same day, the UN reported that the area used to cultivate coca leaf in the Andes fell by 5% last year.

Mr Coke's unexpected capture was a coup for the Jamaican government. On May 17th Bruce Golding, the prime minister, authorised his extradition to America and launched a search for him. The effort caused 73 deaths in firefights between the security forces and his supporters, but found no trace of him.

Yet after a month on the run, Mr Coke decided to turn himself in. Police had conducted raids on his associates, which may have made him think they were closing in. He contacted a pastor to arrange a surrender at the American embassy. But Jamaican police were tipped off and stopped Mr Coke, dressed in a wig and hat, en route.

At first sight, the coca figures are equally encouraging. According to the UN's data, derived from satellite images, the total amount of Andean land under coca has dropped by nearly a quarter since 1990. Colombia has done especially well: partly because it switched from ineffective crop-spraying to large-scale manual eradication, its coca-growing land has been reduced by 60% in the last decade.

Yet it is precisely such achievements that produce the most scepticism about counter-narcotics. The surrender or capture of 27 Jamaican gang leaders in the past month has created a power vacuum that may be filled by bloodshed. As long as political parties depend on the mobs at elections and the police cannot provide security, citizens will still suffer.

Similarly, the drop in land used to grow coca has been offset by better productivity. Since 2000, yields per hectare have risen by nearly two-thirds. And crude machines are replacing bare feet as macerators, while washing machines are being used as makeshift centrifuges. As a result, the UN's current estimate of global cocaine production is 10% higher than it was in 2005.

Moreover, growers continue to find the weak links in the enforcement chain. In 1995 Peru and Bolivia were the world's top cocaine producers. Much blood and money was spent driving the trade out of those countries and, inadvertently, into Colombia (see chart). In 1999 America sponsored a big anti-drug programme in Colombia. As a result, growers have moved back: in the past decade, the area used for coca rose by 55% in Peru and 42% in Bolivia.

Bolivia's president, Evo Morales, still leads a coca-growers' union. He wants the leaf taken off the UN's banned-substances list to allow its industrialisation in drinks and creams. The new constitution passed last year calls coca part of Bolivia's “cultural heritage”. No matter that cocaine is not.

Peru's president, Alan García, refuses to eradicate coca in a key valley, in part to avoid agitating Maoist guerrillas. The UN report found that Peru may have passed Colombia as the world's top coca grower last year. As a senior Mexican official says: “Until legalisation, the only thing you can do is make it someone else's problem.”