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Forty-four years after President Nixon declared "war on drugs", four US states have now agreed to legalise the sale of marijuana and most Americans support legalisation.

Across the world, drug laws are being relaxed, from Uruguay to Portugal, Jamaica and the Czech Republic.

Does this mean the war on drugs has been lost?

The BBC World Service's The Inquiry hears from four expert witnesses, including a former Colombian president and a drugs prosecutor turned defence lawyer.

Bonny Klapper: The legal approach must change dramatically

After many years prosecuting drugs offences as an Assistant US Attorney, growing frustration with the approach inspired Bonny Klapper to become a defence attorney.

Image copyright BERT SARACO......................... Image caption Lawyer Bonnie Klapper argues that drugs offer the only route out of poverty for some

"About 10 years into my career, it really hit me that the people I was prosecuting were not just drug traffickers. They were mothers, they were fathers, and I really began to take an interest in why these individuals got involved in drug trafficking."

One Colombian drug runner had a big impact:

"At 14 he had a choice: go work in the emerald mines, or do something else. So he started in the emerald mines, and it was a horrible experience. And then he was offered the chance to work as a driver for one of the leaders of the Norte Valle Cartel. He started as a driver, and ultimately rose up through the ranks.

"In countries like Colombia, sometimes if you want to support your family - and you don't come from a wealthy family or you're not highly educated - drugs is the only path that you have to get yourself out of poverty."

She noticed other problems back in the US at the other end of the chain:

"[We] would prosecute money remitter houses in Queens that were sending drug money to Colombia. We prosecuted one, we shut it down, and the next day another one opened up in the same location. Or we prosecuted very high level traffickers, either in the US or in Colombia, and once they were extradited, someone else came in to take their place.

"We've shifted the problem from Colombia to Mexico. Now all of Central America is inundated because the traffickers got sophisticated, and they're moving through Guatemala and Honduras, and those countries are turning into narco states."

She argues the approach to drugs users is equally flawed:

"The prison system is a disaster. There's virtually no rehabilitation. Locking up low level individuals who have drug problems or who have limited other options is not effective, because they go to jail, they come out, they get involved with drugs again, and they go right back to it.

"I have nothing but praise for the law enforcement agents I've worked with [but] so many of them have said to me 'we're fighting a war that can't be won the way we're fighting it'.

"The war itself is at a draw. And I believe that draw will be maintained indefinitely unless there's a dramatic change in our approach to drugs and drug trafficking."

Cesar Gaviria: Legalisation taboo is now broken

Former Colombian President Cesar Gaviria worked on the Global Commission on Drug Policy report in 2011 which called on states to decriminalise drugs.

Image copyright Getty Images Image caption Former Colombian President Cesar Gaviria has been a powerful advocate for decriminalisation

"Our recommendation is regulation for everything. That's what Portugal did.

"If you look at the last 50 years, what has been done? In the US, 600,000 people in jail, $40bn (£27bn) of spending a year. The highest rates of consumption of the whole world. You have to say that it doesn't work. It's a failed policy, and public opinion knows that.

"Ten years ago it was unthinkable that the US would move massively to the legalisation of cannabis.

"That taboo has been broken. In the US, a majority of people are talking about approving legalisation of marijuana."

He cites the example of Uruguay, the first country to legalise the marijuana trade.

"All Latin America's looking at Uruguay. It's a country that also looks how to deal with the production, with the supply of the marijuana that is in the state hands.

"I don't expect any major set back of the policy that the Uruguayans have put in place.

"From the beginning in 1961, the objective of the UN Conventions has been to live in a world free of drugs, but it's a utopia. It's something unreachable. It's not to recognise human nature."

David Murray: Real progress has been made

Former chief scientist in the White House Office of National Drug Policy Control David Murray insists the billions of dollars spent tackling drug traffickers and destroying coca crops were well spent:

Image copyright Other Image caption David Murray insists the billions spent tackling drugs trafficking have not been wasted

"A 75% reduction in the productive capacity of Colombian cocaine was achieved by strategic initiatives of supply reduction in partnership with the leadership and political will of the Colombians themselves.

"That's been a sustained achievement that then resulted in a more than 45% drop in the prevalence rate of cocaine use in the United States on the streets

"This is a global business. As a global business they have their preferred mode of operation where they would like to be with regard to supply routes - ungoverned safe havens where they would like to be to carry out their business with maximum efficiency.

"When you push them off of that spot they will adapt but they are diminished.

"We may have an idealised world where prevention and treatment and recovery happen in a certain way and we don't have to do the hard and dirty work, but that's not the reality on the ground.

"The reality is it's a tough slog, it is a cancer and it is worth fighting. Sure it's discouraging to see drug use continue but it actually is diminished if you take a long perspective over time and we actually are making progress with regard to it."

Peter Reuter: Better management is the only solution

Professor Peter Reuter from the school of public policy at the University of Maryland has been a leading academic in the field of drugs policy for decades.

"The war on drugs was partly defined by its rhetoric.

Image copyright other Image caption Professor Peter Reuter says it is simplistic to think the drugs problem can be "solved"

"The need for national leaders to stand up and talk about the scourge of drugs, and signal to the population that [being tough on drugs] was a priority was an important part of the war itself.

"There's going to be less and less of that. I think there's going to be a change both in tone and substance, so the 'war on drugs' will become a less and less plausible metaphor for describing policy. I think it's going to be a public health rhetoric for the foreseeable future.

"I do believe that we have in a sense had an experiment with trying to be very aggressive about controlling drugs through use of prohibition. And we have a sense that that did not work well. And so we're now trying to find better ways of managing the problem, and I think that's welcome.

"If you look at the number of people who are in prison for drug offences, at least in the US, that's an important indicator of the change in real policy, and those numbers are starting to go down. Not dramatically, but they are definitely going down, and many states are making changes that are likely to accelerate that decline."

As drug laws soften he argues the question of regulation becomes key, as happened when gambling was legalised:

"Lottery play was always seen as a bad thing, you legalised it because you wanted to take money away from organised crime, but the result was that the state lotteries became the most aggressive promoters.

Find out more The Inquiry is broadcast on the BBC World Service, Tuesdays from 13:05 GMT Listen to the programme Download the programme

"You have slogans like 'Why be a mug and work when you can play the lottery and win easily?', just the kind of slogan you'd associate with the worst commercial promotion, but done by the state.

"Alcohol is still heavily promoted, and it's promoted in states that have state liquor monopolies, and we've only recently really been able to restrict smoking promotions.

"So I think there's considerable risk that even if there was a monopoly there would be promotion of marijuana, and clearly what we see in the state of Colorado where it is commercially available, it's regulated, like alcohol, what we see is very aggressive promotion, advertising.

"You cannot with a straight face say that marijuana legalisation won't lead to more marijuana dependence.

"Choose your problem. There is no solution. Use of psychoactive drugs is a social problem like a whole lot of other social problems. We manage it. And we may manage it better or worse, but the notion that we solve a problem is simplistic. We're simply managing a problem."

The Inquiry is broadcast on the BBC World Service on Tuesdays from 13:05 GMT. Listen online or download the podcast.