Palmerston North MP Iain Lees-Galloway wants Parliament to consider decriminalising cannabis while discussing legislation to regulate legal highs.

"What we know is that prohibition causes more harm than good," he told the Manawatu Standard.

"It should be science and not politics that determines the relative harms of specific drugs.

"My view is that cannabis would be a good candidate for examination."

Mr Lees-Galloway, Labour's associate health spokesman, was responding to the result of a drug decriminalisation debate on TV3's The Vote.

The show ended with 72 per cent of viewer votes supporting the legalisation of both marijuana and legal highs for the personal use of people aged 18 and over.

"I thought it was an encouraging result," Mr Lees-Galloway said.

"I don't seriously believe that 72 per cent of the country are ready for it, but what it does show is that clearly a significant percentage of the New Zealand public think there is a need to revisit the legislation."

Associate Health Minister Peter Dunne announced yesterday that he was attempting to push through his Psychoactive Substances Bill by mid-July.

The bill, which aims to force legal high manufacturers to prove their products are safe, was originally scheduled to be passed into law by August.

Mr Lees-Galloway said the bill gave Parliament the perfect framework to test the safety and legality of all drugs, using evidence from "rigorous scientific analysis".

He supported Mr Dunne's legislation, but said the legal high K2 should have and could have been banned from dairies a year ago.

Freyberg High School principal Peter Brooks said the debate over legalisation was sending mixed messages to children about the harm caused by drugs.

He was frustrated and horrified that cannabis had been brought into the debate about legal highs.

"The debate on The Vote was ridiculous. It made my blood boil," Mr Brooks said.

"Whatever your views are on cannabis use, it is disastrous for teenagers to see things like this - for them to think it is OK."

"What really frustrates me is that the middle-class experience of marijuana is what the debate is all about when those it really affects are disadvantaged in every way."

Chief executive of Manawatu addiction treatment service MASH Trust, Carol Searle, said legal high addiction had been a pressing issue for Palmerston North in recent months, but cannabis addiction was not a daily issue.

Mrs Searle said the legalisation of marijuana use could increase the number of drug-related issues MASH dealt with. Sitting addicts down and saying they had responsibilities as well as rights would also be difficult, she said.

Palmerston North Detective Sergeant Dave Thompson said it was not the police's place to comment on the politics surrounding drug legislation. They would continue to police cannabis as per the legislation, he said.