Announcement comes as the US state of Oklahoma is poised to become the first to go to trial against drugmakers.

Canada‘s most populous province of Ontario on Monday announced plans to sue opioid makers to recover healthcare costs related to the deadly addiction epidemic.

Ontario’s attorney general, Caroline Mulroney, said the province will join a lawsuit launched last year by British Columbia against more than 40 opioid manufacturers and wholesalers.

According to local media, the province will introduce legislation that, if passed, would allow Ontario to join the proposed class action lawsuit.

“The opioid crisis has cost the people of Ontario enormously, both in terms of lives lost and its effect on healthcare’s front lines,” Mulroney said.

She unveiled legislation to set up the legal action “to battle the ongoing opioid crisis and hold manufacturers and wholesalers accountable for their roles in it.”

More than 10,000 Canadians have died of opioid-related overdoses since 2016, according to government figures. Combatting the crisis is estimated to have cost Ottawa nearly $300m (400 million Canadian dollars).

Alberta, British Columbia and Ontario have been the hardest-hit provinces but the epidemic has affected every part of the country.

The British Columbia suit named opioid manufacturers, wholesalers and distributors as defendants, including Purdue Pharma, whose popular OxyContin drug has been blamed for triggering the crisis.

“These opioid manufacturers and wholesalers failed to warn doctors and the public of the dangers of opioids and marketed them as safer and less addictive than other medications when they were not,” Ontario said in a statement.

Mulroney said Ontario intends to invest any award from the suit in mental health and addiction services.

Neither British Columbia nor Ontario has yet said how much they would be seeking in damages.

Trial to start in Oklahoma

The announcement comes as the US state of Oklahoma is poised to become the first to go to trial against opioid makers.

Several states in the United States have reached settlements with drugmakers, but Tuesday’s trial against consumer products giant Johnson & Johnson and several of its subsidiaries could bring to light documents and testimony that show what the companies knew, when they knew it and how they responded.

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The outcome could also shape negotiations on how to resolve the roughly 1,500 opioid lawsuits filed by state, local and tribal governments. Those have been consolidated before a federal judge in Ohio.

Oklahoma alleges the defendants helped create a public health crisis in the state by extensively marketing highly addictive opioids in a way that overstated their effectiveness and misrepresented addition risk. The drugmakers deny those claims.

On Sunday, Israeli pharmaceutical giant Teva agreed to pay the US state of Oklahoma $85m to settle a lawsuit accusing it of heightening the state’s opioid epidemic, Oklahoma’s attorney general said.

Earlier this year, Oklahoma settled with OxyContin-maker Purdue Pharma for $270m.

Attorney General Mike Hunter said in a statement the Teva settlement shows Oklahoma’s “resolve to hold the defendants in this case accountable for the ongoing opioid overdose and addiction epidemic that continues to claim thousands of lives each year.”

Overdoses from prescription painkillers and heroin – a last-resort illicit drug for opioid addicts – exploded over the last 20 years, according to the National Institute on Drug Abuse.

Nearly 400,000 people died from an overdose involving prescription or illicit opioids from 1999 to 2017, according to the Centers for Disease Control and Prevention (CDC).