“We’re just at the beginning,” Dr. Claude Cyr told Dr. Joe on episode 10 of the Mindspace podcast. He was talking about what we know about the potential positive and negative impact of cannabis on mental health.

Dr. Claude Cyr is a family physician who has been practicing medicine for over twenty years. He judiciously prescribes medical cannabis to his patients.

In 2015, the Prime Minister of Canada, Justin Trudeau, announced his intention to legalize cannabis. One year later, Claude founded Doctors for Responsible Access to bring the medical community into the conversation on legalization.

Now with the end of prohibition in Canada and in a few states in the US, the doors have opened for researchers. We’re just at the beginning of understanding the potential uses and misuses of cannabis.

But what exactly do we currently know about cannabis and its impact on mental health? In episode 10 of the Mindspace podcast, Dr. Cyr shares with Joe his reservations and hopes for cannabis and its potential treatment for mental illness.

Let’s dive in.

Note: If you would like a more in-depth discussion of medical cannabis, Dr. Cyr will be running a one-day training on cannabis and mental health for healthcare professionals at the Mindspace clinic on November 29th, 2019 called “Cannabis Safety – a primer for health professionals.”

The Current State of the Science on Cannabis

“We know about one percent of what the therapeutic potential of cannabis is.”

Dr. Cyr told Joe that when he was attending medical school in the 1980s, we didn’t even know that the endocannabinoid system even existed.

Now we know that there are over a hundred cannabinoids in cannabis. Only two of which have been adequately researched: CBD and THC. And there are probably a dozen or so cannabinoid receptors. Only one of those has been studied to a significant degree: CB-1. These receptors are found all over the body: in the brain, the liver, the lungs, the kidneys, etc. So why is that important?

By isolating and synthesizing each individual cannabinoid, and we can study the interaction they have on each receptor. We can also combine them in different concentrations and see if that also has a particular effect. The possibilities are endless.



Many people with anxiety self-medicate using cannabis. Dr. Cyr said, in short, that this was a bad idea. A short period of euphoria is followed by a depressed mood, elevated anxiety, and withdrawal symptoms. Also, people who self-medicate using cannabis use strains with too much THC and not enough CBD.

However, according to Dr. Cyr there is a possibility that cannabis may be very beneficial for people with anxiety. We just need more studies in order to determine which strain and which dose would have the most benefit.


Two studies came out a couple of years ago. One study followed people with depression who self-medicated, and another followed people with depression whose cannabis use was prescribed and monitored by physicians.

The outcomes were unfavourable for those who self-medicated. However, patients who were monitored by a medical professional fared better.

One possible explanation for this difference in outcomes is that, according to Dr. Cyr, those who self-medicate tend to consume far too much THC (sometime up to a hundred times the dose that is necessary) and not enough CBD.

Interactions with Antidepressants

At small therapeutic doses of THC, the interactions in the liver have not been shown to be significant, Claude told Joe. However, no studies have been done at much higher doses.


“When cannabis is used in palliative care, it does have a tendency to make people forget. What we call aversive memory extinction.”

Dr. Cyr told Joe that the average dose of cannabis used by veterans in Canada is “two to three grams a day.” It is an extremely popular form of self-medication for those that suffer from PTSD. And there might be good reason for that.

“When cannabis is used in palliative care, it does have a tendency to make people forget. What we call aversive memory extinction,” Dr. Cyr said. For example, if patients undergoing chemotherapy are using cannabis before, during, or after treatment, “it’ll help prevent that memory from sticking,” he continued. According to Dr. Cyr, preventing those memories from being hard-wired can be beneficial in certain circumstances.

But is it effective long term? “If you look at certain studies, sometimes the outcomes are worse. If you look at other studies, patients claim that it makes them feel better than all the other medications that they have been using up to date,” Dr. Cyr said.

But again, Dr. Cyr said that there is a lot more research that has to be done.

The Risk of Psychosis

“That’s a huge risk right now.”

Studies have shown that there is a threshold of THC concentration where the risk of psychosis increases significantly. Dr. Cyr warned that people can very easily take “a huge dose of THC in a very short period, which was something probably more difficult to do 30 years ago.”

Two studies were done this year with just over 10,000 students, 4,000 in Montreal and 6,000 in Finland. They examined the link between psychosis and cannabis consumption. The researchers found that the risk for developing psychosis is extremely high in teenagers who had premorbid conditions and had consumed cannabis. But the risk also increases in those without premorbid conditions, just to a lesser degree.

Dr. Cyr warned that teenagers need to be extra careful. “Even if you have no predisposition to schizophrenia, if you start consuming cannabis as a teenager, you may become schizophrenic. And that would never have been your trajectory in life.”

Dr. Cyr added that it is probably dose related, as in a high concentration of THC will likely increase that risk. However, including a higher concentration of CBD may help reduce that risk, but more research is  needed to confirm this.

So do we stop all teenagers from consuming cannabis? Dr. Cyr says no. “We may have to put up with a certain amount of risk.” Dr. Cyr added, “but if we can prevent the high risk teenagers from consuming early, promoting the importance of CBD, and therefore reduce the harm collectively, I think that’s something that’s more realistic than just saying, ‘Just say no.’”


“If it causes euphoria, if it releases dopamine, it’s addictive.”

However, Dr. Cyr adds, when compared to other drugs like cocaine or nicotine, the rate of addiction is much lower. The addiction rate with cannabis is around 9%, compared to cocaine, which is around 20%, and nicotine, which is around 30%.

The problem is that in “young people addiction is much higher than in adults,” which Dr. Cyr said is around 16%. He warns that “there is something with the teenage brain and cannabis, which is different than the adult brain and cannabis.”


Cognitive Functioning

“People who consume cannabis containing only THC, have trouble with memory, attention span, and concentration,” Dr. Cyr said. However, the good news is that after around 30 days of abstinence, most of these symptoms gradually go away. But Dr. Cyr warned that problems with attention may persist for longer.


This is a controversial issue according to Dr. Cyr.

He said that some scientists and doctors believe that while under the influence of cannabis complex tasks might become more difficult to perform since it has an impact on executive functioning. “So [cannabis users] might stop doing complicated things like studying for example because it requires too much mental effort,” he told Dr. Joe.


Cannabis is a very popular sleep aid. However, does it produce restful sleep? Dr. Cyr says it depends. According to some, it does, but there hasn’t been a lot of studies. Dr. Cyr also added that “CBD may cause insomnia.”

For his patients, if they haven’t responded to any other medication, he would prescribe synthetic THC. In some of his patients, it finally permitted them to sleep. But Dr. Cyr only prescribes cannabis as a form of last line of defence.

Some doctors argue that cannabis is safer than other sleep-aids like valium and that they rather prescribe it as a first line of defence for people suffering from insomnia.

. . . . .

There is so much more to be discovered about cannabis, whether about its positive or negative effects. And according to Dr. Cyr, we’re at the very beginning. With the end of prohibition in Canada, doors for researchers have been wide opened. So for now, we’ll have to wait, and perhaps we might have to wait awhile.

“We’ll talk in 5 to 10 years,” Dr. Cyr told Dr. Joe.

And we’ll be listening.