Chloe Swarbrick has come out swinging in defence of marijuana legalisation, saying opponents are "ill-informed" and confusing legalisation with liberalisation.

The first-term Green Party MP sparred with anti-legalisation campaigner Duncan Garner on Monday morning, the host of The AM Show telling her making the Class C drug legal will see more kids getting high than ever before.

The Government is still working on the exact wording of a referendum that'll be held at the next general election, but Ms Swarbrick says the public will know exactly what they're voting for - and it won't be liberalisation, because that's what we already have.

"What we currently have right now is essentially a free-for-all," she told Garner.

"Whether you are 15 or 50 years old and you want to get your hands on cannabis in this country this week, are you going to be able to? Absolutely, you are... Everybody in this country knows somebody who knows somebody who is going to be able to deal or sell you illegal cannabis.

"That illegal drug dealer is not going to check your ID; they are not going to know the chemical balance of THC, CBD... within that cannabis; they are not going to be paying their tax; and worse than that, that is going to provide profit to a criminal underground. This is currently the state of play in this country."

She played down fears cannabis shops would spring up on street corners overnight, saying we've had the chance to learn from experiments in legalisation overseas.