One pro-cannabis legislation advocate says the Prime Minister should say how she will vote in the referendum. 

Jacinda Ardern's remaining tight lipped on how she'll vote in the cannabis referendum, declining once again to share her view during last night's leaders debate.

She did, however, admit she's tried the drug 'a long time ago'.

Former MP Nandor Tanczos, who is campaigning with Make it Legal, told Heather du Plessis-Allan that Ardern should say as she is the Prime Minister and other leaders have made their thoughts clear. 

"We've seen other political parties who are not at all adverse about sharing their views."

He also says it's about permission - as it's much more politically courageous to take a pro-legalisation point of view. 

"If the Prime Minister can state her position, I think it would give other people who are scared to state their view, it would give them permission."

Tanczos says that you can assume her position, as she has gone on the record and said people should not be criminalised based on cannabis use. 

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• Heather du Plessis-Allan: Jacinda Ardern doesn't have to confess cannabis vote