"It is that kind of evidence that has led us to the firm view that cannabis should be dealt with as a health issue rather than as a criminal justice issue.
"Those countries which have approached cannabis from a health perspective, and have put in place laws which enable cannabis to be properly controlled by government, have been far more effective than we have in preventing cannabis use among young people."
The Internet Party was in favour of decriminalisation of cultivation and possession of cannabis for personal use, and the development of a government-regulated production and distribution system, based on international best practice and expert advice, she said.
Controls would be put in place to protect young people, Ms Harre said, adding that the "objective has to be to reduce use".
Ms Harre and Mana Party leader Hone Harawira this week denied any tension in the Internet-Mana camp over the issue of cannabis law reform following the leaking of an expletive-laden email from Mr Harawira protesting against a planned online advertisement.
Ms Harre said the area where the two leaders shared "common ground" was over the legalisation of the drug for medical use, and having a review of current drug laws from a health perspective.
The NZ Drug Foundation also backs a health-based approach, although executive director Ross Bell said he did not support full decriminalisation.
New Zealand's criminal justice approach to dealing with cannabis was "backwards" and obsolete, he said.
"This research shows that cannabis use is problematic for young New Zealanders, yet we have quite a limited response to address that."
Paul Rout, chief executive of the Alcohol and Drug Association of New Zealand, said the findings showed discussions around law reform needed to "look at the full range of implications for all age groups".
Both Mr Ross and Mr Rout said finding a way to encourage young people to delay the age they started using cannabis, such as to the age of 25, would go some way to prevent long-term damage.
