It was the picture of the perfect Toronto family--David Carmichael, a nationally-known fitness guru, his two children and wife, Elizabeth.

"We had a great life," says David. But in 2003, with mounting financial pressures and increasing work demands, David began to change in ways that alarmed his mother, Doreen.

"He lost weight very quickly--and his colour changed. It was not his normal colouring. It was more gray... and it wasn't the way it should have been," she says.

David went to his family doctor, explained his symptoms and was told he was in a major depression. His doctor prescribed a daily dose of 40 mgs of Paxil, one in a group of antidepressants called SSRIs, or Selective Serotonin Reuptake Inhibitors.

After eight months, David was feeling himself again, and weaned himself off the drug.

But a year later, in the summer of 2004, depression returned with a vengeance.

"It was like a freight train. You know, the symptoms just suddenly reappeared and within a matter of days I knew I was in trouble."

Instead of going back to his doctor, David started himself back on 40 mgs of Paxil.

What David didn't know was that new studies were raising concerns about the side-effects of SSRIs, and that by mid-2004, Health Canada was advising Canadians of stronger warnings for SSRIs and other newer anti-depressants. These new warnings indicated that patients taking these drugs may experience behavioural or emotional changes that could increase their risk of harming themselves, or others.

"I started to have suicidal thoughts after I put myself back on Paxil," he explains.

The drug wasn't working for him the way it did the first time, and he'd read in a book that a dosage up to 60 mgs was safe, so he upped his own dose.

"I became delusional, I started thinking that my son was in a living hell," says David.

Ian Carmichael, then 11, did have some minor learning disabilities, but he also had a winning personality and a passion for BMX biking that David encouraged. He had had a few epileptic seizures, but in David's mind, the epilepsy became permanent damage. David fell under the delusion that Ian was going to become violent and hurt other children.

What David didn't know was that he was falling into a deep state of psychosis.

"When you're in that state, you don't realize that your mind is thinking in such a distorted way," he says.

On July 31st, 2004, under psychotic delusions, David took Ian to a hotel in London, Ontario, and strangled him.

David was charged with first-degree murder, but found not criminally responsible due to his mental illness, and transferred to the forensic psychiatric facility at the Brockville Mental Health Centre in Ontario for treatment.

What wasn't brought up in court, was whether the drug he was on at the time had anything to do with David's psychotic state.

"... it has the pattern of 50 or 100 cases I've looked at fairly closely where people have committed mayhem, murder or suicide under psychiatric drugs," says American psychiatrist Dr. Peter Breggin.

"The pattern is that the person stopped the drugs and then started the drug. Carmichael started the drug again, less than three weeks before he kills his child. And what we find is that it's that initial few weeks when the drug has the most impact, when it's either increased in dose, decreased in dose, or stopped."

W-FIVE approached GlaxoSmithKline, the makers of Paxil, for an interview on possible links between their antidepressant and this violent act, but they declined to participate. In a newspaper report this summer, spokesperson Peter Schram said:"David Carmichael's case is certainly a terrible tragedy, however we do not believe Paxil played any part in this situation."

Dr. John Bradford, forensic psychiatrist with the Royal Ottawa Health Care Group, does not subscribe to the theory that Paxil triggered David's psychosis. He was one of the first to assess David's mental health after the tragedy.

"I'm not purely in myself entirely convinced it's the drugs that are at fault," he says. "I think it would be a very wrong message to give. These drugs have ... helped millions of people and I have no reservation in prescribing them. I've been prescribing them for years."

We may never know exactly what caused David's psychotic state, which leads to the question, could it happen again?

Dr. Bradford says it's unlikely. What he's more worried about is whether David can ever really forgive himself for killing Ian.

"...David is doing well at this time, but I'd always worry about suicide risk in the future, because whether he is actually able to ever come to absolute terms with himself about forgiving David for what he did is going to be an open question."