A drug researcher says legalising cannabis would take control out of the hands of criminals.

A cabinet paper has been leaked to the National Party, which contains four options for a referendum at the 2020 election on the decriminalisation of cannabis for recreational use.

Independent drug researcher, Geoff Noller, told Mike Hosking our current approach to cannabis isn't working.

"What we currently have doesn't work. Cannabis has been illegal in New Zealand since 1926...we have got one of the highest rates of use in the world, we have high youth rates...basically, all the ills that are attributed to cannabis haven't dissipated as a consequence of the policies that we have got."

He said we need to rethink the way we deal with the problem.

"People basically have access to cannabis as much as they want anyway. There is no quality control over that cannabis and the people who are organising and controlling the supply are criminals."

"There is a whole range of reasons why thinking differently about cannabis would be a good thing."

Noller said regulating any policy is going to be the biggest problem.