Long-term cannabis use could be elevating stress and anxiety levels in young adults, according to a new study by Toronto's Centre for Addiction and Mental Health.

The study's lead author, Dr. Romina Mizrahi, said the perception is so widespread that cannabis helps users cope with anxiety and stress that her team expected to see that in its results.

Instead, "this is exactly the opposite of what we were hypothesizing," said Mizrahi, the senior scientist at CAMH's Campbell Family Mental Health Research Institute.

The study was published in the psychiatric journal JAMA Wednesday, and was funded by the National Institute of Mental Health in the U.S.

Rather than finding that a brain protein linked to stress and anxiety decreased in people who had used cannabis regularly over a year, researchers found inflammation of that protein went up in study participants.

The protein is significant because it's one of the indicators of depression, stress and anxiety. When tested, the study participants had increased levels of the protein, Mizrahi said.

The CAMH team tested 24 people in their 20s who used cannabis at least four times a week and had been doing so for a year.

Participants told the researchers "they like to feel high but they also feel that it helps them with their experiences," though none of them were clinically depressed or diagnosed with anxiety disorders, Mizrahi said.

The study measured the 18-kDa translocator protein, referred to as TSPO, through imaging and blood tests to assess what happened when someone used cannabis.

Cannabis use creates 'vicious cycle,' psychiatrist believes

Dr. Clive Chamberlain, staff psychiatrist at CAMH and Toronto's Hospital for Sick Children, has a caseload of 50 patients aged 14 to 24. Many of them are daily cannabis users who are "self medicating," he said.

"They've discovered at least in the moment when they're smoking marijuana, it relieves them of some anxiety or low mood," he said.

He believed it's creating a "vicious cycle," because they don't notice that it "lowers their threshold for anxiety so they gradually become more and more anxious."

At this time of year, annually, he said he treats students who have to leave university studies because of heightened anxiety and he often finds they're also daily cannabis users.

His evidence is exclusively observational, working as a psychiatrist for the last 50 years.

A slide showing the difference in the presence of the brain protein TPSO between a regular cannabis user and someone who doesn't use the drug. (CAMH)

"We have very poor research. Because [cannabis has] been illegal for so long we lack the kind of well controlled studies to guide us on this," he said.

But his experience with young adults hinted at the still early findings of Mizrahi's study.

"I think the big question is what happens long term," Mizrahi said.

She agreed that, depending on the strain and a user's genetic makeup, "they could feel a reduction in their stress levels," but whether that lasts is still unknown.

Mizrahi is not prepared to come right out and establish a link between long-term cannabis use and elevated stress or anxiety.

Her study looked at regular users. Now she wants to study people who abstain from cannabis use and measure their TPSO levels.

"I need to establish a cause," she said.