Canada's premiers say they will not be ready for the legalization of cannabis next summer if Ottawa does not clarify how to solve several public-health issues associated with ending 94 years of prohibition, such as how to prevent people from driving while high.

Alberta Premier Rachel Notley told the closing news conference at the leaders' annual summer meeting in Edmonton that provinces need guidance on five problems: road safety and enforcement, preparation and training on distribution, taxation, public education, and how supply and demand of the legal drug might affect the black market. It is still possible that recreational cannabis will be available to all Canadians by July 1, 2018, she said, but much more work needs to be done over the next year if the provinces are to be ready.

"Premiers around this table agreed that, should the federal government not engage adequately on these issues, we will need more time to implement the federal government's decision," Ms. Notley said. "We expect, with the greatest respect, that the Prime Minister will review the concerns that have been delineated in our communiqué, because they are not insignificant."

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Earlier in the day, Manitoba Premier Brian Pallister failed to get his counterparts to issue a joint call for the federal government to delay by a year the implementation of Prime Minister Justin Trudeau's pledge to legalize the drug so that the potential harms of legalization can be better minimized.

"He needs to then hear what the premiers of his country – our country – have said we need help with," Mr. Pallister said. "There are a number of significant and serious public policy issues here. They need to be addressed. They should be addressed co-operatively."

Instead of calling for a delay, the premiers agreed to form a working group to identify common concerns, seek answers from Ottawa and to provide recommendations by November on how best to legalize the drug.

To date, the federal government has indicated that it will leave the contentious issues of regulating the wholesale distribution and retailing of cannabis up to the provinces and territories, a move that industry insiders and academics have predicted could hamper the uniform rollout of legalization across all jurisdictions.

The federal task force report guiding the government's legalization of cannabis recommended against selling the drug in liquor stores, stating concerns that mixing alcohol and marijuana leads to higher levels of intoxication. Before the task force issued its report last December, politicians in British Columbia, Manitoba and Ontario floated the idea of selling cannabis at such government-run outlets. Pharmacies, or private shops such as dispensaries that are currently illegal under federal drug laws, are also possible venues, according to experts.

Asked about the premiers' concerns on Wednesday in Quebec City, Mr. Trudeau said the goal is still to have the law passed by next summer. He said that young people have easy access to marijuana now but should not, and criminals and streets gangs are making millions through illegal sales.

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"We need to put an end to this policy that does not work," Mr. Trudeau said. "We are continuing to work with the provinces to make sure the framework will be in place a soon as possible."

Michael DeVillaer, a drug-policy expert at McMaster University, said the premiers are wise to call for help on this complex file because, inevitably, they and municipal politicians will have to solve problems related to making cannabis legal. He said that the three most widely used legal drugs – tobacco, alcohol and opioids – have all produced massive public-health costs related to harms such as lung cancer, injuries caused by excessive drinking and an epidemic of fatal overdoses.

"What we're seeing in the big picture is three legal, profit-driven drug industries and we have three public health crises," Prof. DeVillaer said. "So it would be naive to assume this one is going to go swimmingly without problems."

The Canadian Association of Chiefs of Police on Wednesday concluded a national conference in Montreal at which president Mario Harel warned that the black market will not simply disappear when recreational cannabis becomes legal. He added that extra funds will be needed for equipment and to train officers to detect drug-impaired drivers.

Mr. Harel, who is police chief in Gatineau, suggested about 2,000 such experts will be needed and estimated Canada has about 600 now.

With a report from The Canadian Press