More than 100 legal cannabis shops opened across Canada, where the government has thrown out pot convictions.

An online survey has found just 19 per cent support for retaining the current prohibition policy for recreational cannabis use.

Nearly three-quarters of those who took part had used cannabis in the previous six months. Despite that, Associate Professor Chris Wilkins, who led the study, said he thought respondents were a good broad demographic representation of the population, although with some bias.

The New Zealand Drug Trends Survey was carried out between November and February. It was promoted through a targeted Facebook campaign and was completed by more than 6300 people.

They were asked which of 10 options they favoured for managing recreational cannabis use, ranging from the present prohibition, through to a profit-driven market with no restrictions.

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AP Cannabis growing California-style. A new survey suggests Kiwis aren't keen on such widespread commercialisation.

More than 6300 people completed the survey, although 36 per cent did not indicate a preference.

Of about 4100 people who did show a preference, the most popular option was for home production and use only, with 27 per cent support.

Another 21 per cent favoured a profit-driven market with light restrictions, similar to that in force for alcohol, while 19 per cent wanted to keep the existing situation with prohibition and criminal penalties.

New Zealanders were due to vote in a referendum on legalising the personal use of cannabis by the 2020 general election at the latest. The referendum was part of the confidence and supply agreement between Labour and the Greens.

The same goal also sought increased funding for alcohol and drug addiction services, and to ensure drug use was treated as a health issue.

Prime Minister Jacinda Ardern said the Government had yet to finalise a decision on the timing of the referendum.

ROSA WOODS/STUFF Police Association president Chris Cahill has asked police to consider where they stand on frontline officers using cannabis if it becomes legal, especially after critical incidents like a police shooting.

"Obviously we need to make that decision quite soon to get everything in place, but we also need to work on the question, and that's something that's obviously going to be really key, making sure that we're making the best use of going out and asking New Zealanders," she said on The AM Show on Tuesday.

"So the level of detail that's being put out will be an important consideration."

Wilkins, who led a drug research team, said respondents to the self-selecting online survey broadly resembled the demographic profile and regional distribution of the wider New Zealand population.

Obviously people interested in the issue were more likely to take part, but an online survey was more likely to reach younger people than were surveys carried out by landline, or by visiting people at their home.

Of those who answered the survey, 45 per cent were female, 21 per cent were Māori, 65 per cent were employed, 18 per cent were students and 11 per cent were unemployed. The average age was 29, and the range was 16 to 87.

123RF The survey found significant support for doctors or pharmacies being able to provide medicinal cannabis.

Seventy-three per cent of the sample reported using cannabis, 33 per cent ecstasy, 26 per cent LSD, 20 per cent methamphetamine, 11 per cent cocaine and 5 per cent morphine in the previous six months.

Wilkins said he was personally in favour of some kind of reform but didn't want to see a fully commercial option adopted.

He was interested in a community trust approach. Basically that was not-for-profit with a requirement to give some money back to the community for such things as youth sports and drug treatment and prevention. Under that option, the community would have a say about such things as the number of retail outlets.

The fact more than a third of respondents to the survey did not have a policy preference for the regulation of cannabis suggested more information and public debate was needed on the different options, Wilkins said.

It was important the Government's referendum presented the full range of reform options available, including home production, not-for-profit and heavily regulated market options.

Concerns had been raised about the profit-driven legal cannabis regimes in some parts of the US. Those concerns included declining cannabis prices, increasing use of high-potency extracts, accidental poisonings from cannabis edibles, use of unregulated pesticides, aggressive marketing of new cannabis products and cannabis industry influence on regulation.

The survey also asked respondents for their preferences on the regulation of medicinal cannabis.

Of nearly 3900 with a preference, 41 per cent favoured cannabis provided by doctors or pharmacies, 14 per cent supported the current approach of prohibition with a ministerial option, with another 14 per cent favouring home production and use only.