Catholic Bishop Don Bolen said the Saskatoon diocese is looking for exorcism expert to help when people exhibit signs they are possessed by a demon. (CBC)

An Ontario science advocacy group says it wants medical authorities to ban exorcisms in Canada, following a recent Saskatoon incident involving a man who carved "hell" on his chest.

Alleged demon-expelling rituals can be physically stressful to the subject and are sometimes dangerous, according to the Toronto-based Centre for Inquiry Canada.

The centre was responding to a story reported by CBC last week.

In that report, the bishop for the Catholic diocese of Saskatoon confirmed that a local priest had dealt with a case of possible demonic possession. Bishop Don Bolen also said it's possible the man was experiencing a mental breakdown.

It all happened several weeks ago when a priest was called to a home by a woman who said her uncle showed signs of being possessed by the devil. The woman believed a priest's blessing could help the distraught man.

The man had used a sharp instrument to carve the word "hell" on his chest.

When the priest entered the room, the man spoke in the third person, saying "He belongs to me. Get out of here," using a strange voice, according to church officials.

The priest told CBC News that he decided to call police, for safety reasons.

While there was no formal exorcism ritual performed, the priest blessed the man, saying he belonged to the good side, to Jesus. That seemed to help.

Since then, Catholic Church leaders in Saskatoon have been considering whether Saskatoon needs a trained exorcist and are consulting with their counterparts in Calgary.

Centre for Inquiry spokesman Justin Trottier says that scares him more than demonic possession.

He says exorcisms have worsened existing medical conditions, caused bodily harm, and have occasionally resulted in death.

Most cases of claimed demonic possession are, in fact, mental conditions that need medical treatment.

"We have individuals performing essentially psychiatric, psychological or medical treatments of some kind," he said. "They're obviously not regulated by any real authority, and we don't quite know what they're doing."

Trottier said he's also troubled by the secrecy surrounding possession and exorcisms.

"So we don't know the prevalence of exorcisms in Canada. We don't know who's doing them, we don't even really know what they're doing," he said.

The Centre for Inquiry describes itself as a humanist group. It received considerable media attention last year with its "There's probably no God" bus billboard campaign.