Labor backbencher Michael Pettersson will introduce a bill that would effectively legalise cannabis for personal use, when the ACT's parliament resumes sitting this week.

It's a private members bill, meaning it has not been signed off on by cabinet nor is it official ACT Labor policy.

The ACT decriminalised cannabis possession for amounts under 25g in 1992 through a scheme called the Simple Cannabis Offence Notice.

The scheme aimed to curb unnecessary involvement with the criminal justice system and reduce the cost of policing cannabis use.

The limit was later raised to 50g after it became apparent people were still being arrested, as cannabis was sold by the ounce which equates to about 28g.

However the number of plants an individual could have was reduced from five to two to compensate for the higher threshold.

Mr Pettersson said he believed the territory's current drug laws were not working.

“About 60 per cent of drug arrests in the ACT are for cannabis consumers. That’s not suppliers, that’s consumers. I think police can spend their time doing better things than going after people using small amounts of cannabis," Mr Pettersson said.

His bill would remove cannabis possession of less than than 50g by an adult as an offence and therefore legalise it, according to its explanatory statement.

It would also allow people to legally have four cannabis plants.

Mr Pettersson said allowing people to grow their own supply would prevent them from interacting with drug dealers, who could potentially sell them harder drugs.

“I want to reduce the exposure individuals have to drug dealers and organised criminal cartels. I think by allowing people to grow their own supply does that," he said.

Minors would still be fined $160 or have to enter the diversionary program if caught with the drug, and the cultivation, trafficking and sale of cannabis would continue to be against the law.

But Mr Pettersson said adults should not be forced to face the criminal justice system for the possession of small amounts of cannabis for personal use.

“Thirty-five per cent of Australians have tried cannabis and 10 per cent of Australians have tried it in the past 12 months. This is not a rare substance, this is incredibly commonplace across Australia and I think it’s time we change our drug laws," Mr Pettersson said.

The bill will be tabled in the Legislative Assembly on Wednesday.

It comes as a Senate inquiry recommends scrapping a private member's bill from Liberal Democrats Senator David Leyonhjelm. The bill would have removed Commonwealth restrictions on the recreational use of cannabis.

Legalising cannabis would save about $100 million in Commonwealth policing costs and increase GST revenue by about $300 million, Senator Leyonhjelm said.

However the Department of Health told the inquiry while many Australians saw cannabis as harmless, almost a quarter of Australia's drug and alcohol treatment services were being provided to people identifying cannabis as their principal drug of concern - about the same as amphetamine use.

The Australian Medical Association said the costings that underpinned the Leyonhjelm bill were of "low reliability" and did not take into account the extra investment in treatment services that would be needed if the drug was used more widely.

National Drug Research Institute director Professor Simon Lenton said while he did not support the Leyonhjelm bill in its current form, he was keen for a broader discussion about a non-prohibition model for cannabis in Australia and in the states and territories.