Many First Nation teenagers who leave home to come to Thunder Bay, Ont., for high school are suffering from post-traumatic stress disorder (PTSD), according to a high school nurse in the city.

Mae Katt testified on Tuesday at an inquest into the deaths of seven First Nations students who died in Thunder Bay between 2000 and 2011.

"In the last seven or eight years, we're seeing a lot more acute conditions of mental health and substance use," said Katt, who has been serving remote First Nations as a nurse for more than 30 years.

The students exhibit symptoms of PTSD including excessive worry, sleeplessness, headaches and "early psychosis" such as "auditory hallucinations — hearing voices," Katt said. 

Mae Katt

Mae Katt is a nurse at Dennis Franklin Cromarty First Nations High School in Thunder Bay who says students soothe their feelings with drugs and alcohol when feeling low. (Mae Katt/Twitter)

The nurse attributes the mental illness to "25 years of a suicide crisis that never got addressed" in northern Ontario's First Nations. 

There have been more than 500 suicides among the approximately 45,000 First Nations people who live in the region in that time, Katt said.

The current generation of students is the first to be raised in the "sub-culture of suicide," where their parents use drugs to cope with unresolved trauma, grief and loss, she explained.

"Adults are not doing drugs by choice. If you look at what hasn't been done in the north, no one has invested to stop the suicide crisis," Katt noted.

"Students tell me: if you really want to help us, help our home communities," the nurse told the inquest.

Nurse says students feel 'devalued'

But life in the city isn't easy for the students, either, according to Katt.

She said students talk to the school nurses about feeling "devalued" in Thunder Bay, adding that the "devaluing is related to their race" in a city where "no one really knows who they are."

"We try to make them strong to try to make them understand they shouldn't be treated the way they're treated," Katt explained.

The nurses' efforts don't always work and when students "feel pretty low, their reaction is poor-decision making," she said. "They soothe their feelings through drugs and alcohol."

Dennis Franklin Cromarty First Nations High School, where Katt works, started a suboxone treatment program five years ago for students who are addicted to opioids.

Katt said 50 students have taken part in the program and 11 have graduated. 

Watch live streaming video from the First Nation student deaths inquest here.

Follow CBC Thunder Bay reporter Jody Porter as she tweets from the inquest.