He added that people had mistakenly thought the referendum was about medicinal cannabis, and had changed their minds from 'yes' to 'no' when they realised it was about personal use.

But Drug Foundation executive director Ross Bell said the downward trend in 'yes' support was because of "well-funded and relentless opposition scaremongering".

He has asked supporters to donate funds to the 'yes' campaign, which was putting together a strategy that included billboards, TV advertising and social media.

McCoskrie responded by saying he was giving the public the "facts", adding that he had little faith in the Prime Minister's expert advisory panel, headed by her Chief Science Advisor Professor Juliet Gerrard.

The panel is putting together publicly-available information about the impacts of cannabis use, what changes have occurred overseas, and how applicable that might be in New Zealand.

McCoskrie added that the Drug Foundation was partly Government-funded.

"I wish we had deep pockets," he said.

The 'no' campaign was gathering a coalition of community organisations that included former cops and drug counsellors, educators and business people who would "benefit from legalisation but have kids and don't want to go down this track".

The UMR poll was based on an online survey of a representative sample of 1000 New Zealanders aged 18 and over, with a margin of error of 3.1 per cent.

Respondents were asked if they would vote for or against legalisation of cannabis, and were asked again after being told about measures in the draft bill including a ban on selling cannabis to anyone under 20, a purchase limit of 14 grams, and limits on how much one can grow at home.

Meanwhile support for euthanasia, which will also be the subject of a referendum vote on September 19, also appears to be falling.

This week's Newshub Reid Research poll showed 62 per cent support for Act leader David Seymour's End of Life Choice bill, while 24 per cent opposed. This is down from 71 per cent support in a 2018 poll from the same company.

Support was also down in this week's 1 News Colmar Brunton poll, which had previously been between 72 and 76 per cent support but had dropped to 65 per cent.

Seymour rejected any suggestion that public support for euthanasia was falling, noting that those polled were asked different questions.

"The polls show more people support the concept than will commit to a specific vote eight months out [from the election]," he added.

Fewer teens trying cannabis

New research has suggested the number of Kiwi teens who have tried cannabis is dropping.

New data from the Youth Insights Survey, published yesterday in the New Zealand Medical Journal, found that between 2012 and 2018, the proportion of Year 10 students who had tried the drug fell by more than a quarter.

"This was predicted, since cannabis trends in this age group are strongly associated with tobacco trends, and it was already known that smoking in Year 10 students had continued to decline since 2012," said the study's Otago University authors.

However, the authors note that other research shows cannabis use is increasing among New Zealand adults generally.

Past year use increased from 9 per cent in 2012/13 to 15 per cent in 2018/19 overall - and from 19 per cent to 29 per cent among 15 to 24 year olds, the age group with the highest cannabis usage.

The authors said there were likely two key reasons for the conflicting trends.

"Firstly, the average age at which young people are initiating risk behaviours, including cannabis use, has increased in recent years," they wrote.

"Secondly, normalisation of cannabis use has been counteracted by decreasing prevalence and frequency of smoking and drinking in this age group.

"The evidence suggests that adolescents' willingness to try cannabis has increased, but their opportunities for doing so have decreased due to less face to face time with friends and fewer drinking and smoking occasions."

- Jamie Morton