DAVOS, Switzerland (AFP) - Colombian President Juan Manuel Santos has called for a scientifically backed international effort to weigh the consequences of legalising marijuana, urging a coherent joint policy to tackle the scourge of drugs.

"We must approach this problem internationally, otherwise we'll take it from one place to another," Mr Santos said, speaking on Thursday at the annual World Economic Forum in Davos.

The issue of whether to legalise drug use for personal use has shot to the fore since Uruguay in December became the first country in the world to oversee the production and distribution of marijuana.

The law authorises the production, distribution and sale of marijuana, allows individuals to grow their own on a small scale, and creates consumer clubs - all under state supervision and control.

The government has three months remaining to devise the specific rules and regulations, which comes as two US states have moved to decriminalise marijuana.

While the use of medical marijuana has been around for some time in many American states, Colorado and Washington are creating a recreational market in which local authorities will oversee the growing, distribution and marketing of the drug - all of it legal - for people to get high just for the fun of it.

But Mr Santos insisted there was now a "major contradiction" in drug policies.

"How can I tell the peasant that is growing marijuana in the mountains of Colombia that he will go to jail, if smoking marijuana is legal in Colorado or Washington?," Mr Santos asked during the forum.

He highlighted that the Organisation of American States (OAS) has been mandated to explore the issue of legalisation within the context of the fight against the organised and brutal drug-trafficking cartels making billions of dollars a year in smuggling drugs around the world.

Only once all the aspects, including public health, had been studied would it be possible to start talking about a new policy approach and make a decision, he insisted.

According to the United Nations, about 90 per cent of the cocaine consumed in the United States passes through Mexico and central America - a region that also counts among the world's most violent.

The OAS is studying the new approach, after concluding in 2012 that the traditional methods of fighting drug use - supported by the US government - have failed to stop drug trafficking.

Mr Santos, who is set to run for re-election this year, also said the merits of each drug had to be studied, arguing "marijuana is different from cocaine, and cocaine is different from heroin".

An effective tool against the cartels is also to confiscate their assets, he said, regretting that a banking industry which insists on secrecy was a serious impediment.

Controversial Texas governor Rick Perry said he was not in favour of locking up every young person who had tried drugs.

"I think science has a very important role to play, before deciding at the level of legalisation or decriminalisation," he stressed.

Adding fuel to the mix, US President Barack Obama, who has admitted to smoking pot as a youth, earlier this month welcomed the moves by Colorado and Washington.

"It's important for society not to have a situation in which a large portion of people have at one time or another broken the law and only a select few get punished," he told the New Yorker magazine in an interview.

Couching his remarks somewhat, Mr Obama called the move in the two states a challenging "experiment".

"Those who argue that legalising marijuana is a panacea and it solves all these social problems, I think are probably overstating the case," he added, stopping short of calling for legalising the drug at the federal level.

The United States currently funds Plan Colombia, a US$9-billion anti-narcotics effort launched in 2000 that includes a counter-insurgency element.

Peace talks between the Colombian government and Marxist FARC rebels have been underway in Havana since November 2012.

Negotiators are currently discussing how to deal with drug trafficking, an industry that has fuelled the conflict.