Laws passed on Wednesday in the ACT Legislative Assembly, which come into effect January 31, would make possessing 50 grams of cannabis or cultivating two plants legal.

Mr Barr said any federal intervention to overturn the laws would be "a massive overreaction".

Attorney-General Christian Porter previously described the laws as "crazy" and a "very bad idea", while Deputy Prime Minister Michael McCormack on Friday morning told reporters the laws were "madness".

"Here's the ACT government probably spending too much time smoking hooch themselves, then wanting to legalise the stuff," he said.

Mr Barr said the Commonwealth government should be focusing on more important issues.

"And that's matters of large scale criminal gangs and national level and international level drug trafficking, rather than becoming obsessed with small scale personal use within the ACT," he told The Canberra Times.

"I presume none of them are arguing that recreational users should find themselves behind bars for two years which is what the Commonwealth Criminal Code allows for."

Mr Barr said it would not be easy for the Coalition government to overturn the laws, requiring the support of the Senate.

"It's a difficult path for them, it's not as straightforward as it used to be," he said.

"They will beat their chest as they want to do but they've got bigger issues to worry about I would have thought."

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Mr Barr said he presumed the Senate would not readily pass the laws and at the very least it would go through an inquiry process.

If the Coalition did seek to overturn the laws, Mr Barr said the government would lobby the cross-bench Senators.

Asked whether there were plans to decriminalise other drugs like MDMA, he said said further harm minimisation laws could be on the agenda at "some time in the future".

But he said it wouldn't be happening in the next four to five years.

"We've got a three year review on this so in between this issue and pill testing that's out to the mid 2020s, so I wouldn't suggest anyone hold their breath on anything else at this point," Mr Barr said.

The Opposition says the comments show the legalisation of cannabis was just the first step in a broader agenda of weakening drug laws.

"As we've seen from jurisdictions overseas, like Amsterdam and Colorado, the negative consequences of increased crime and health issues, particularly mental health, should worry Canberrans," shadow Attorney-General Jeremy Hanson said.

"The Canberra Liberals do not support changing laws that could potentially put our young people at risk."