'A bit unusual': Police grapple with possibility of cannabis legalisation

Senior police officers are grappling with how they'll deal with cannabis if it's legalised.

It's the hot-button topic at the Police Association's annual conference in Wellington this week.

If the public supports legalisation, even police themselves could be lighting up, which Police Association president Chris Cahill says is just a sign of the changing times.

"From my point of view, it's a little bit foreign and you'd sort of go, 'Ooh that's a bit unusual' - but society changes."

Police Minister Stuart Nash says there will be clear expectations for officers under legalisation.

"You wouldn't expect an officer to turn up drunk - in fact, if they did turn up drunk, they'd be in a heap of trouble," he said.

"If marijuana did become legal you certainly wouldn't expect an officer to turn up stoned either."

As part of Labour's coalition deal with the Greens, there has to be a referendum on legalising cannabis on or before the 2020 election.

The Police Association isn't taking a position on the vote, but wants to talk how any law change would impact their job.

Mr Cahill says there's a raft of considerations.

"Tools for road side drug testing, establishment of a standard of impairment, rules around edibles and oils, clarification of how many plants an individual could grow at home."

Canada will fully legalise cannabis next week, and medicinal use is already allowed. Their police force is taking a relaxed approach to the change.

"Just because we're adding another substance that people can consume, I don't think we need to light our hair on fire or overreact to this change," says Canadian Police Association president Tom Stamatakis.

He says Canadian police are ready because they've been dealing with cannabis for years.

He also says New Zealand has an advantage - we can learn from Canada's experience before making our own changes.