TORONTO -- Chloe Grace Moretz says her starring turn in the Canadian/Irish co-production "Brain on Fire" is "the role of a lifetime."

The "Kick-Ass" actress plays a young woman battling a terrifying auto immune disease that attacks her brain and causes hallucinations, paranoia and psychotic violent outbursts.

It's only with the support of family, friends and the last-minute intervention of a diligent doctor that she's properly diagnosed and saved from a lifetime of psychiatric institutions.

"You get to kind of break a lot of stereotypes that surround people with illnesses," Moretz told a press conference at the Toronto International Film Festival on Friday.

"I think above all, it's more than a movie about illness, it's a story about labelling and mislabelling, and misunderstanding and how far a misunderstanding can go."

The film, which made its world premiere at the fest, is based on the book of the same name by Susannah Cahalan, whose promising career as a New York Post reporter unravelled quickly with an unexplained illness that also attacked her ability to form memories.

The real-life Cahalan was on hand to describe her harrowing journey, although she could only reconstruct the tale by interviewing others about what they witnessed.

"Some of my memories now are actually of Chloe doing the things, which is bizarre," said Cahalan, who lost about two months of her life.

"It's just blank, maybe a few glimmers of things that are very unreliable but mainly blank. However, in the process of recreating and in the process of watching a movie about your process of recreating, I've created a lot of false memories, too."

Irish director Gerard Barrett said he hopes the film can shed light on a little-known condition that is often misunderstood.

"It's very rare that you get to make a film that will probably save a life and I think by putting this film out there and dealing with the disease and talking about the disease and highlighting the disease I think ultimately it will save a life in some way, shape or form," said Barrett, who was brought on board by producer Charlize Theron.

"There's a greater good in it. And that's what really attracted me to it."

Tyler Perry and Jenny Slate play co-workers, while Richard Armitage and Carrie-Anne Moss play her devoted family.

The real-life doctor who saved Cahalan, Dr. Souhel Najjar, said he faced a "huge" challenge in convincing colleagues she had a neurological -- rather than psychological -- condition.

He said Cahalan has become the voice for many people who can't advocate for themselves, calling it "truly an honour to be her doctor."

Najjar bemoaned "tremendous gaps" between medical disciplines -- especially psychiatry and neurology -- and stressed the importance of simply listening to the patient and their family in order to find important diagnostic clues.

"We don't treat the patient sometimes as a whole. We treat symptoms and disease and we forget that behind that symptom there's a human being," said Najjar.

"We need to learn to treat the patient as a whole.... Nothing replaces sitting, not standing, in front of the patient. Just sit next to the patient."

The Toronto International Film Festival wraps Sunday.