A debate over cannabis reform got heated this morning after Mike Hosking called Green MP Chloe Swarbrick "naive" and told her to "wait until you have kids".

Swarbrick was invited onto Hosking's Newstalk ZB show after she responded on social media to his column about a poll showing 52 per cent of New Zealanders intended to vote against cannabis legalisation in the 2020 referendum.

In his column, Hosking said the poll proved "middle New Zealand doesn't want a bar of this Government's barking madness over drug liberalisation".

The debate started with Hosking describing Swarbrick as part of the "pro pot brigade".

Swarbrick immediately responded: "I am in the sensible regulation brigade."

The pair then challenged each other over various pieces of evidence both for and against cannabis legalisation.

Swarbrick said statistics showed that the majority of New Zealanders had tried cannabis, and would have procured it through illegal means. She compared it to the black market during alcohol prohibition, and said money spent policing cannabis would be better spent on harm intervention.

Hosking then compared that logic to other social ills.

"We failed on domestic violence. Why don't we legalise that as well? It is a stupid argument."

Mike Hosking told Green MP Chloe Swarbrick she was "naive" over cannabis reform. Photo / File

Swarbrick said drug use was different, and needed to be treated as a health issue.

Hosking said if marijuana was legalised it would lead to increased use and an increase in harm, such as with alcohol.

"We can learn from issues there. There is corporate, free-market control that seeks to exploit vulnerable communities to make a quick buck.

"We need a system that provides for intervention."

Hosking said at the end of the day it came down to politics.

"You guys want to legalise it, and at the moment you are losing the battle.

"People like me have been around a while, had some children, raised a family, have seen the damage and danger of this and have more experience than people like you, who don't."

Swarbrick said she had seen the damage and the danger to people, and under prohibition we were just "pushing them into the shadows" where they were not able to access help.

The aim of legalising cannabis was not to increase access but to be able to regulate it, Swarbrick said.

"Is it easier for kids to get their hands on alcohol or cannabis?"

Hosking responded that Swarbrick was "naive".

"With the greatest of respect, at the age of 24 or 25 you're naive. You don't have kids, haven't raised a family, don't know what teenagers get up to.

"Come back to me when you're 54 and have lived a bit of life and understand, and have been through a bit and know what you're talking about."

Swarbrick said it was OK to dismiss her because of her age, but the debate needed to be based on evidence.

"If you want to dismiss me, Mike, that is all very well and good, but I don't think that is a very good or useful way of engaging.

"I've been citing evidence and been willing to engage in that evidence with you."

Hosking responded: "You've cited no evidence, I've counteracted you with facts and figures that are irrefutable."

Swarbrick said she was "frequently dismissed" on the basis of her age, and challenged Hosking to invite Dr Benedikt Fischer, a professor of addiction research at the University of Auckland, onto the show to engage with the science.

At the end of the debate Hosking said of the upcoming referendum: "I suspect we will win."

"I am interested in more than just winning," Swarbrick responded.

"I am interested in meaningful conversation with New Zealanders about how to reduce harm, a far more complex and nuanced debate than simple, binary chanting of 'we will win'."