The opioid crisis may be causing a drop in Canadians' life expectancy, according to a report released Tuesday by Canada's chief public health officer.

That comes as no surprise to Yvonne Clark, whose son Conner, 21, died on Thanksgiving in 2013 after suffering from an OxyContin addiction for almost two years. An overdose from a single fentanyl tablet killed him, the Calgary woman told CBC News.

"This drug is cruel. It's evil," she said. "Kids are going out there and they think it's not going to happen to themselves, [that] they're invincible."

Clark, 54, now goes out and shares Conner's story with students, hoping to save lives. But she knows the enormity of the killer she's trying to fight.

"I really do think this drug is going to claim the lives of many more. And it's devastating," she said.

In her annual report on the state of public health in Canada, Dr. Theresa Tam said that for many years, life expectancy has been "steadily increasing," as it is in other high-income countries. But the opioid crisis is expected to stop that progress in its tracks.

"This is the most significant public health crisis that we've seen for many decades," Tam told CBC News.

Dr. Theresa Tam, chief public health officer for Canada, says the opioid crisis is expected to halt the country's steady increase in life expectancy. (Public Health Agency of Canada/Canadian Press)

Overdose deaths have been climbing, killing nearly 4,000 Canadians in 2017 alone. Canada hasn't seen deaths that could impact life expectancy like this since the AIDS epidemic of the 1980s — or the 1918 Spanish flu pandemic, Tam said.

In British Columbia, the province hit earliest and hardest by the fentanyl crisis, drug overdose deaths contributed to a decrease of 0.12 years — more than a month — in life expectancy between 2014 and 2016.

Although the data is not yet available to determine whether there's a similar effect on a national level, Tam said the Public Health Agency of Canada is working to find out — and believes the deaths of "so many people in such a short period of time will cause this dip" in other provinces and territories.

Average life expectancy already decreased in British Columbia by more than a month between 2014 and 2016 due to overdose deaths. (Darryl Dyck/Canadian Press)

The increase in deaths in the last few years seems to be driven by illegal fentanyl, as well as overdoses resulting from using other drugs — including alcohol, benzodiazepenes, cocaine or methamphetamines — in combination with opioids, the report said.

The U.S. saw a drop in life expectancy due to drug overdoses for two years in a row, according to the Centers for Disease Control and Prevention.

National data suggest the majority of opioid overdose deaths in Canada have been men and individuals between 20 and 59 years old, but Tam cautioned that this may not reflect the reality in some regions.

"Emerging evidence from several provinces indicates that individuals living in poverty, First Nations people and those who experience unstable housing are disproportionately affected by opioid overdose deaths," she said.

The report, meant to be a glimpse at the state of public health in Canada for the year, focuses on substance abuse among youth, including alcohol, cannabis and opioids.