Toronto man’s trial leaves many asking: Can excessive marijuana use lead to psychosis?

Yes, smoking pot can trigger psychosis. But, no, smoking a few joints is not the equivalent of a “get out of jail free” card.

That’s what we should retain from the case of Mark Phillips, who received a light sentence in an assault case after the court accepted the argument that the 37-year-old was suffering from “marijuana-induced psychosis.”

The case has caused much consternation, for a couple of reasons. The assault itself was horrible: On Dec. 7, in St. Thomas, Ont., Mr. Phillips attacked a family of immigrants in a parking lot because they were speaking Spanish, breaking one man’s ribs with a baseball bat while yelling that he was a terrorist. The incident was filmed and posted on YouTube.

He pleaded guilty to assault causing harm (after originally being charged with aggravated assault) and received a conditional discharge, meaning that after serving three years’ probation, doing 240 hours of community service and refraining from consuming all non-prescription drugs during the probation period, he will not have a criminal record.

The sentence has miffed many. The case leaves the impression that a well-to-do white man (Mr. Phillips is a Toronto lawyer) has been treated with kid gloves by the courts. His defence – that his seemingly racist attack was caused by consumption of marijuana – has also been widely mocked.

Let’s leave the arguments about race – and income – and status-based double-standards in the justice system to others and focus on the medical aspect of the case – namely: Can cannabis cause psychosis?

That question is hotly debated in scientific circles and the answer seems to be a mitigated yes.

First, we need to understand what psychosis is – a mental disorder in which thought and emotions are so impaired that contact is lost with external reality. (It is not the same as hallucinations.)

Psychosis is quite rare – fewer than three in 100 people will experience a psychotic episode in their lifetime. People who smoke or otherwise consume cannabis, especially in significant quantities, have a higher incidence.

But correlation is not the same as causation.

Some people have vulnerability, a genetic predisposition to psychosis, and cannabis can be a trigger, as can other things like trauma or amphetamines. Severe mental illness like schizophrenia tends to arise in late teens and early adulthood, the same time young people tend to experiment with drugs, so the psychosis can be coincidental. Finally, many people with severe mental illnesses that feature psychotic episodes self-medicate, with cigarettes, alcohol and cannabis.

In other words, it’s a classic chicken-and-egg scenario: It’s not clear which comes first, mental illness or cannabis use.

There are also incidents recorded where consuming significant amounts of cannabis seems to be an actual trigger for psychosis – and that’s what the court heard from an expert witness in the case of Mr. Phillips.

The evening of the attack he smoked at least three or four joints. He did so routinely, and also routinely felt he was being threatened by terrorists.

Mr. Phillips told his therapist that he has been purchasing cannabis at dispensaries, six to eight grams at a time, for a significant time period. This was not casual use.

Dr. Peter Collins, a forensic psychiatrist at the Centre for Addiction and Mental Health in Toronto, also said Mr. Phillips’s symptoms of paranoia and his feelings of persecution dissipated when he was not smoking cannabis.

What is fascinating, and little discussed about this case, is that Mr. Phillips did not claim he was “not criminally responsible” due to mental illness. That would be a much harder case to make.

He actually pleaded guilty, but said his cannabis-induced psychosis should be a mitigating factor in sentencing – a position that was accepted by both the Crown prosecutor and the judge.

One can debate whether or not the court was right to grant him some slack. But there is little evidence that this case will set much of a precedent.

The argument made in the case was not that someone impaired by cannabis cannot commit a crime but rather that, in rare instances, cannabis use can cause temporary mental illness.

That’s a tough case to make and it’s going to be even tougher to make after the scrutiny this ruling has rightfully inspired.

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