New Zealand has a number of models to examine if the government seriously considers decriminalising marijuana.

There's been an explosion in the number of countries and states liberalising its use over the past two decades - some have legalised it entirely, while others have decriminalised it only for medicinal use.

Amsterdam has its infamous coffee shops, which take advantage of a policy of tolerance, Portugal has changed possession to an administrative as opposed to a criminal offence, and in the US four states - Colorado, Oregon, Washington and Alaska - have legalised cannabis, but certain restrictions remain in place.

Photo: AFP

But what model works best, what impact has decriminalisation had elsewhere, and what would work here?

The question became prominent this week after Associate Health Minister Peter Dunne said he was not sure New Zealand's law was efficient, and he was considering a more tolerant approach.

Police Association president Greg O'Connor then came out and described the US state of Colorado as a 'model' given it had tackled both use and supply. He distinguished this from the Netherlands which he said had done nothing to regulate drug dealers.

Mr O'Connor wouldn't say whether or not he supported the adoption of a Colorado-style approach in New Zealand.

But, he favoured the Colorado model, so what's really the difference between Colorado and the Netherlands' approach? Quite a lot, it turns out.

Photo: AFP

New Zealand Drug Foundation executive director Ross Bell says Colorado's model is based on a free-market and commercialisation logic, where supply was more controlled, and it was a more direct way of getting rid of the black market.

The Netherlands' approach was more hybrid, with police turning a blind eye to criminal activity behind the scenes.

"The way it is described, it is ok if cannabis goes out the front door but there is still a big question mark on how it gets in the back door.

"The supply is fundamentally still in the hands of the criminals" he says.

Colorado - The first US state to legalise cannabis

Colorado decriminalised medical marijuana in 2001 and voted to legalise the drug all together in 2013. The first retail shops opened in January 2014. While the drug is legal, some restrictions remain in place.

Colorado's law states:

You have to be older than 21 to buy, use or possess marijuana

You can only buy it from licensed retailers, who are the only people who can legally sell it

You can have up to one ounce of marijuana, and can give one ounce to someone, but can't sell it

You can grow up to six plants

You cannot use it in a public place or on federal land, such as a national park

Marijuana sold from retailers has to be sealed and labelled

Given the law change in Colorado is relatively recent, the true effect is yet to be seen. Not only that, but official figures are contradictory, leaving a murky picture of the impact it has had.

Photo: US Government

A 2015 report by the federal government's Rocky Mountain High Intensity Drug Trafficking Area Program, which monitors the Colorado area, found a 32 percent increase in marijuana-related traffic deaths from 2013 to 2014.

"In 2014, when retail marijuana businesses began operating, toxicology reports with positive marijuana results of active THC results for primarily driving under the influence have increased 45 percent in just one year," the report stated.

But traffic fatalities were down overall, according to the Colorado Department of Transportation, and overall crime also decreased.

Figures on the number of people who use cannabis vary, but show that people in Colorado generally use it more than those in other states.

Advocates argue legalising marijuana leads to more money and more jobs, fewer arrests and frees up police resources.

There have been fewer drug arrests and charges since the law in Colorado came into effect, and a total of $US138 million (approximately NZ$200m) raised in specific marijuana tax revenue in the first two years.

Photo: US Government

The US Justice Department's 2015 National Drug Threat Assessment Summary said while it was too early to determine the impact from legalisation across the four states, the total marijuana seized from the southern border - from Mexico, where most in the US comes from - declined more than 23 percent from 2013 to 2014.

"Cartel intentions and the possible impact of domestic legalisation initiatives are continuing intelligence gaps relative to the levels of Mexican marijuana entering the United States," the report stated.

It argued state legalisation would allow domestic criminal organisations "to cultivate and traffic marijuana with more freedom than in the past".

But counter-arguments to that say that Colorado's decriminalisation will ultimately take the power away from criminal organisations, as buyers will purchase it from licensed retailers and could be prosecuted if they buy it elsewhere.

Netherlands - Marijuana leniency since 1976

While cannabis isn't legal in the Netherlands, the government doesn't prosecute people for using or possessing small amounts. Selling what the government calls "soft drugs" in its so-called coffee shops is also illegal, but it doesn't prosecute for the offence.

Amsterdam, in particular, is known world-wide for its coffee shops where locals and tourists alike gather to share a joint or indulge in marijuana cookies. While the Netherlands has a tolerant approach, figures show locals smoke less than in other European countries.

Photo: AFP

However, tourists flocking there to make the most of the country's 'freedom' have added to what the government sees as a growing nuisance and crime problem. As a result, it is now focussing on coffee shops becoming smaller and concentrating more on the local market. It's also introduced a new toleration rule, allowing only Netherlands' residents into coffee shops. However most cities have used local powers to keep the shops open to foreigners.

Unlike Colorado, it is against the law to grow marijuana and possess it in the Netherlands. However, police will generally only seize the plants if there are five or fewer, but may prosecute if there are more.

Netherlands' law states:

Selling, buying and using soft drugs is illegal, but people won't be prosecuted for small amounts

Users can have no more than five grams (almost a sixth of what is allowed in Colorado) or five cannabis plants - and these may be seized

You have to be over 18 to purchase marijuana from a coffee shop

Coffee shops are not allowed to sell alcohol alongside cannabis

While the Netherlands' law is lenient compared to other countries, local authorities argue it doesn't go far enough. In 2014 a group of mayors put pressure on the justice department to allow them to licence legal suppliers.

They wanted the government to legalise cultivation, arguing the current laws forced coffee shops to rely on illegal gangs, which in turn encouraged illegal activity and took up police resources.

What would work in New Zealand?

Ross Bell, of the NZ Drug Foundation, favours Portugal's approach to drugs when considering what would work in New Zealand.

Portugal decriminalised the use of all drugs in 2001 and decided to make drug-use a health issue, not a criminal issue. People found with drugs may now receive a small fine, but they won't be locked up - they might be referred for treatment instead.

"You're not just changing the legal status of the drug, you're replacing the criminal side with a much more interventionist health approach," Mr Bell said.

Cannabis use, alongside other low-level drug use, such as BZP and synthetic cannabis, should be decriminalised and regulated, Mr Bell said.

"That strips the power from the gangs."

As it is, these drugs are circling in the black market, among a "whole lot of weird, unknown substances".

Mr Bell looks to the District of Columbia which changed its approach towards marijuana as recently as last year. It legalised its use, but not the trade in it, so under a new law, people can grow it, use it and give it away, but they can't sell it.

This is most closely in line with how Kiwis use it, Mr Bell said, suggesting it could be a starting point for discussion here.

"If you think of the way Kiwis use cannabis, often they're not getting it from the tinny house.

"It might be the first thing we allow is for people to grow and give."