When it comes to treating addiction and potentially legalising drugs, New Zealand should look at role models like Portugal where the system is based on "compassion and love", an expert has said.

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Journalist Johann Hari spent several years researching addiction for his book, Chasing the Scream and is in New Zealand for a three-day conference in Rotorua where the nation's drug problems will be discussed.

Mr Hari told TVNZ1's Breakfast that he learned the common understanding of addiction is fundamentally misunderstood.

"When I started researching this question about seven years ago now, you know I was in a real state of confusion, I wanted to help the people I loved, but I couldn’t see how to do it, so I ended up going on this quite big journey all over the world," he said.

"The core of what I learned is that I, and many of us, have profoundly misunderstood what addiction is and that's led us to misguided answers here in New Zealand and across the world."

Mr Hari says research by Canadian psychology Professor Bruce Alexander showed that addiction was not simply a matter of a person craving a substance, heroin for example, that has a chemical hook.

The professor did a series of experiments in the 1970s where he gave two groups of rats the option of drinking water or water laced with heroin.

One of the groups was left alone in cages while the others were in a cage dubbed "rat park", where the rats had company, plenty of food and things to play with.

Professor Alexander found that the rats in the cage dubbed "rat heaven" never overdosed on the heroin-laced water.

"When rats have the things they need in life, they don’t find compulsive drug use compelling, and there's a lot of human parallels," Mr Hari said.

"This shows us the opposite of addiction is connection."

Dramatic turnaround in Portugal

Mr Hari said Portugal was the leading nation when it came to adopting this approach after a dramatic turnaround from 2000.

At the turn of the century, Portugal had one of the worst drug crisis in the world, with one per cent of its population addicted to heroin.

"Every year, they tried the American way more, which is followed in New Zealand but not as harshly, imprison people, shame people, give them criminal records and every year, just like here, the problem got worse," Mr Hari said.

On the advice of experts, Portugal legalised drugs and invested money into not only residential rehab but also therapy and job creation programs for addicts.

"The goal was to say to every person with an addiction problem in Portugal, we love you, we value you, we’re on your side, we want you back," Hari said.

The changes saw an 80 per cent reduction in injecting drug use and even those that had criticised the legalisation of drugs were convinced, Mr Hari.

"I went to the places that have the most loving and compassionate approaches, Portugal, Switzerland, what are the results? Their drug crises have massively reduced."

"For 100 years now, we've been singing war songs about people with addiction problems, we should have been singing love songs to them all along."

'We’ve got to start copying the models that have succeeded'

Referencing a potential referendum on the legalisation of cannabis, Mr Hari implored New Zealand to stop following models that have failed.

He said we should look at the nations who have legalised drugs, where he says, "they are not having 40 people die a year from synthetic cannabis the way you are here in New Zealand".

"New Zealand is spending a huge amount of money making people with addiction problems worse, what they did in Portugal, is they took that money and they transferred it to making people better."

"At the moment, what you guys are doing here in New Zealand, what we’re doing in my country Britain, is we’re copying the places that failed."