Fifteen years ago, if you were walking along the streets of Perth or Canberra with a small amount of cannabis in your pocket and you were stopped by police, you would have been treated pretty much the same way.

Key points: WA decriminalised cannabis in 2004 under Labor premier Geoff Gallop

WA decriminalised cannabis in 2004 under Labor premier Geoff Gallop The Barnett Liberal government's "tough on crime" approach overturned the laws

The Barnett Liberal government's "tough on crime" approach overturned the laws Cannabis use did not go up in WA when it was decriminalised, according to surveys

You would have been given an infringement notice, not charged with a crime.

In 2004, WA joined the ACT in decriminalising cannabis, meaning it was not legal to carry it for your own personal use, but if caught you wouldn't get a criminal record for doing so.

But fast forward to this week and — thanks to very different political winds — your stroll could take a decidedly different turn depending on which city you were in.

The ACT has just become the first jurisdiction in the nation to legalise cannabis for personal use, with its Parliament passing a private members bill by Labor MP Michael Pettersson.

From January 31 next year, any adult can possess up to 50 grams of dry cannabis, although it can't be consumed in public, and will be able to grow two plants.

While some doubt has been cast about the law's longevity, with federal Attorney-General Christian Porter not ruling out overturning it, the ACT and WA are moving further and further apart in their cannabis laws.

A 'tough on crime' approach

In WA, Colin Barnett's Liberal government — which included Mr Porter as state attorney-general before he moved to federal politics — repealed the cannabis reforms as part of a "tough on crime" approach in 2011.

Former WA premier Colin Barnett re-criminalised cannabis possession. ( ABC News: Andrew O'Connor )

It was the culmination of a long Liberal campaign against the laws, introduced under former Labor premier Geoff Gallop.

"More people than would otherwise have been the case will not only experiment with, but also use or perhaps cultivate cannabis, become addicted, move on to harder drugs and die," Mr Barnett told the WA Parliament in 2003.

"Young people will lose their lives because of this legislation.

"I know that sounds dramatic, but it is a fact."

Choose treatment instead of fines

But Dr Gallop, who recently joined the panel of an international think-tank on drug reform, said the 2004 law had met their intended goal of treating the personal use of cannabis as a health issue rather than a crime.

It meant people found with up to 30g of cannabis were given a fine, with the option of paying it, challenging it in court or undertaking treatment in lieu of payment.

"Really, on all fronts it was a success story," he said.

"It decriminalised, it provided penalties for people but not criminal penalties and there was no increase in the use of cannabis in the community.

"So from our point of view, our objective was achieved."

Former WA Labor premier Geoff Gallop decriminalised cannabis in the state. ( ABC News: Eliza Laschon )

As a long-term campaigner for drug reform and an advocate for the decriminalisation of all drugs, Dr Gallop was frustrated that the laws were repealed.

He said that decriminalisation was an important first step towards legalisation.

"Our view is you have to cross that bridge first," he said.

"Lots of other people follow after you cross it, but you have to win the argument that the criminal law should not apply.

"But really that's the one we wanted to address up front and show people that life goes on, that there are no negative effects that follow from decriminalisation and then we can look at the drug issue more broadly."

No jump in cannabis use in WA post-reform

Professor Steve Allsop of the National Drug Research Institute was one of the experts involved in designing the WA scheme, after it was recommended by a drug summit convened by the state government.

He said official surveys showed there was no change in cannabis use in WA after the laws were introduced, although cannabis use had not increased in other jurisdictions either.

In hindsight, he said the scheme was introduced with the best intentions and approach, but the process could have been managed better.

For example, he said the public was never really educated on the difference between decriminalisation and legalisation.

Decriminalisation, he said, was like driving through a red light.

"It's not right and you shouldn't do it, but if you get caught police will only give you an infringement notice and not charge you," he said.

Steve Allsop says more education would have helped the public better understand the law changes in WA. ( ABC News: Eliza Borello )

Professor Allsop also said while treating cannabis possession as a health issue was the right approach, some people would have been better served by advice and education rather than expensive treatment.

It was also difficult for many people living in regional areas to access treatment.

He said many politicians of different political stripes supported the health approach, although they did not always show this publicly.

"I think there was genuine political concern and then there was political opportunity," he said.

While Dr Gallop maintained he had broad community support for the laws, he said there were pockets of opposition.

"There were sections that didn't like it," he said.

"The say-no-to-everythings didn't like it, the Liberal party didn't like it because Labor was doing it."