The cannabis debate: It's not as simple as 'legal' or 'illegal'. So what's the difference between depenalisation, decriminalisation and legalisation?

Imagine a future in which the possession of cannabis in New Zealand is no longer a criminal offence.

If you're caught with a small quantity, instead of being arrested you get a 'cannabis warning' and, perhaps, a fine.

The drug is confiscated and destroyed and you have to appear in front of a panel whose members include a health professional, a lawyer, and a psychologist.

You're still not allowed to grow any plants or sell the drug but you don't get a criminal record, although there is a system for recording warning notices (which is accessible in some cases when applying for a job).

This is what decriminalisation looks like. It's often confused with legalisation.

Drug Foundation executive director Ross Bell said the legal concepts underpinning decriminalisation and legalisation are poorly understood.

Supplied Decriminalising cannabis has gained momentum around the world.

"In my mind we use legalisation as a code word for commercialisation. As soon as you remove all criminal penalties, essentially you have legalisation.

"I think there's a whole lot of confusion."

The New Zealand Drug Foundation supports a Portugal-style system on decriminalised recreational drug use, so let's take that as an example.

Should New Zealand legalise cannabis? Share your stories, photos and videos. Contribute

It's widely believed recreational drugs are legal in Portugal. They're not.

In 2001, Portugal was the first country to decriminalise all recreational use of drugs including heroin, cocaine, ecstasy, and LSD - but you still can't grow or sell your own.

The focus has switched from criminal justice and punitive remedies to one in which health, social costs, and treatment were at the forefront.

But the Portuguese system is still criticised by some of its interventions, Bell said.

"At a [Portugal-style] panel if you are somebody with a drug dependency you get referred to treatment but there are still penalties. It becomes a civil penalty that can include a fine, a speeding ticket-type infringement offence.

"A lot of people criticised it as too paternalistic but it does open up that referral. The other thing Portugal did was remove the ability to be sent to prison for personal use."

CAMERON BURNELL/FAIRFAX NZ Drug Foundation executive director Ross Bell also supports the Portuguese system of decriminalisation.

So if that's decriminalisation - what about legalisation?

One of the main differences between the two ideas is the ability to commercially produce and sell cannabis under legalisation.

Marijuana is legal in Uruguay, Spain, and in Colorado and Washington states in America, with different restrictions on growing, consuming and selling.

In Uruguay, cultivation is managed by the government - at least in theory. Adults can access cannabis by joining a cannabis co-op, growing up to six plants at home, and buying it from licensed pharmacies. The psychoactive ingredient tetrahydrocannabinol (THC) of the commercially available product is capped at 15 per cent and, if growing at home or in a club, an individual is limited to 480g per person per year.

Spain never criminalised possession of drugs for personal use and what emerged was the toleration of personal possession and supply for non-commercial use. The selling part is a grey area, but people get around that by forming private members' clubs.

In Washington DC, it's illegal to sell recreationally, but it's fine to possess, grow in small amounts, and gift the drug.

STEVE DIPAOLA/REUTERS Displays at Shango Cannabis shop in Portland, Oregon, in 2015.

So, broadly then, legalisation translates as using, producing, growing, transporting, or supplying a substance as a commodity like any other, with restrictions attached.

It doesn't mean lawless, or a free-for-all.

In this sense, cannabis is controlled and consumed in a similar manner to alcohol, or regulated harmful substances, such as tobacco. Or regulated industries, such as gambling.

REUTERS In Uruguay, adults can grow up to six cannabis plants at home.

This is a way off for New Zealand, if it ever happens, Bell said.

"I think there are probably merits to that but I wouldn't want to take that approach. We'd need a stepped approach, get the public comfortable because you could change your drug laws and do it really badly.

"Essentially what Peter Dunne has proposed, that's our approach as well. Decriminalise with health referrals, using the Psychoactive Substances Act to regulate the sale."

Decriminalisation involves removing the criminal penalties for possession, for example, personal use, with a sliding scale in terms of personal limits, potential civil penalties, and health referrals.

Cannabis is already effectively decriminalised in New Zealand to a certain extent under the diversion system - in small amounts and in cases where it's a first offence.

However, young people are routinely convicted for cannabis possession, mostly young men and, within that demographic, mostly young Maori men, Bell said.

About 2000 young people aged 17-25 are convicted for drug possession each year. The average sentence is 65 days at a cost of $16,250 per person, which amounts to $29 million a year.

Young people are being imprisoned for repeat possession offences, leaving them with criminal convictions that limit travel and future opportunities, Bell said.

Under a decriminalised system, recreational drugs users would not face the same ramifications in other areas of their lives.

Critics of decriminalisation point to a potential range of problems: increased availability leading to more use; difficulties in comparing different countries' policies; the fact decriminalisation does not fix the social, health and justice questions around drug use.

Last year, UK drug policy charity Release conducted a global roundup of drug policies.

What emerged is this: the harms of criminalisation "far outweigh" the harms of decriminalisation.

In other words, a punitive approach does very little to reduce rates of drug use, which are on an upward trend and have been for years.

"[One] conclusion that can be drawn is the doomsday predictions are simply wrong, and removing criminal sanctions for possession and use of drugs does not lead to skyrocketing prevalence rates."