The war on drugs has failed and should make way for a global shift towards decriminalising cannabis use and promoting harm reduction, says the former president of Brazil, writing today in the Observer. Fernando Henrique Cardoso argues that the hardline approach has brought "disastrous" consequences for Latin America, which has been the frontline in the war on drug cultivation for decades, while failing to change the continent's position as the largest exporter of cocaine and marijuana.

His intervention, which will reignite growing debate in Europe about how to tackle drugs, was welcomed yesterday by campaigners for drug law reform who increasingly see the impact on developing countries where drugs are produced as critical to the argument.

"After decades of overflights, interdictions, spraying and raids on jungle drug factories, Latin America remains the world's largest exporter of cocaine and marijuana," Cardoso writes. "It is producing more and more opium and heroin. It is developing the capacity to mass produce synthetic drugs. Continuing the drugs war with more of the same is ludicrous."

Cardoso, a sociologist, said Argentina, Mexico, Colombia, Bolivia and Ecuador had all now taken steps towards drug law liberalisation and that change was "imminent" in Brazil. The way forward worldwide would involve a "strategy of reaching out, patiently and persistently, to the users and not the continued waging of a misguided and counterproductive war that makes the users, rather than the drug lords, the primary victims," he added.

Danny Kushlick of Transform, which campaigns for drug liberalisation, said Cardoso's intervention illustrated the human cost of efforts to combat the drugs trade on often poor and underdeveloped producer countries: "Until this problem is taken up as a development issue it's not going to move anywhere. The default position is that this is a problem of addiction, but people have completely missed the point of the war on drugs, that the vastly detrimental effects are largely in production and transit. If you look at a nation state like Guinea Bissau, which was a fragile state before and now is a fragile narco-state, that is a prime example of the vulnerability of developing countries to the fact that these drugs are incredibly expensive."

Cardoso's article follows the conclusions published earlier this year of a commission on drugs composed of three former Latin American leaders, who had been lobbying Washington for a change in its conduct of the war on drugs. Barack Obama's election to the White House is viewed as an opportunity for fresh thinking, with Cardoso among guests invited to a discussion on drugs policy with him before he became president.