Argentina and Mexico have taken significant steps towards decriminalising drugs amid a growing Latin American backlash against the US-sponsored “war on drugs”.

Argentina’s supreme court has ruled it unconstitutional to punish people for using marijuana for personal consumption, an eagerly awaited judgment that gave the government the green light to push for further liberalisation.

It followed Mexico’s decision to stop prosecuting people for possession of relatively small quantities of marijuana, cocaine, heroin and other drugs. Instead, they will be referred to clinics and treated as patients, not criminals.

Brazil and Ecuador are also considering partial decriminalisation as part of a regional swing away from a decades-old policy of crackdowns still favoured by Washington.

“The tide is clearly turning. The ‘war on drugs’ strategy has failed,” Fernando Henrique Cardoso, a former Brazilian president, told the Guardian. Earlier this year, he and two former presidents of Colombia and Mexico published a landmark report calling for a new departure.

“The report of the Latin American Commission on Drugs and Democracy has certainly helped to open up the debate about more humane and efficient policies. But, most of all, the facts are speaking by themselves,” said Cardoso.

Reform campaigners have long argued that criminalisation enriched drug cartels, fuelled savage turf wars, corrupted state institutions and filled prisons with addicts who presented no real threat to society.

The US used its considerable influence to keep Latin America and the UN wedded to hardline policies which kept the focus on interdictions and jail sentences for consumers as well as dealers. The “war” was first declared by the Nixon administration.