CanadaHealth Cannabis and mental health: Harm reduction strategies Laura Tennant March 10, 2020 Share Twitter Facebook Share Print (AnthonyJess/AdobeStock)

There is a well-documented link between cannabis and the onset of psychosis in vulnerable individuals. Typically, guidelines recommend that people with a history of mental illness, either individually or in their family, should avoid cannabis at all costs. Approximately 1 in 5 Canadians and Americans experience a mental health condition each year, and approximately 1 in 33 Canadians will experience psychosis in their lifetime, with similar numbers in the States.

But is abstinence the only option? Or might there be some middle ground, where people can consume cannabis while taking measures to protect themselves?

There is little consensus on the specifics of the complicated relationship between cannabis and mental health, although the association between cannabis use and mental illness is well-documented. Some experts staunchly insist that cannabis causes mental illness, while others believe the data reflects the fact that people with a predisposition to mental illness are more likely to be attracted to cannabis.

But what almost everyone can agree on is that people with a personal or familial history of mental illness, in particular, psychosis, should take action to reduce harm if they do choose to consume cannabis.

There are many choices that can reduce potential mental health risks of cannabis consumption.

What are the mental health risks of cannabis?

The main mental health risk of cannabis consumption is developing psychosis, the experience of losing contact with reality. The symptoms vary among individuals, but may include unusual thoughts, seeing or hearing things that are not there, and paranoid or delusional beliefs.

While THC can cause paranoia in people without mental illnesses, the evidence suggests that those who develop full-blown psychotic illness in response to cannabis use were likely predisposed to it in the first place.

There is also some evidence suggesting that people who have mental health vulnerabilities may be more likely to try cannabis, rather than cannabis causing their mental illness.

Depression and heavy use of cannabis are also associated, but similarly, it is unclear if the association is causal, or if shared factors may increase the likelihood of both cannabis consumption and depression.

Strategies for lower risk cannabis consumption

Most physicians recommend a person abstain from cannabis if they have a personal or family history of mental illness. If someone chooses to consume cannabis anyway, there are a few ways to reduce harm.

The Centre for Addictions and Mental Health (CAMH), along with Health Canada, has produced a set of lower risk cannabis use guidelines.



The key issue, I think, here really has to do with brain development. One would want to minimize use before the brain is developed. And I would usually say ideally until 24 or 25. But I mean, it has to be after the age of 21, for sure. Dr. Romina Mizrahi, CAMH

The guidelines explain that abstinence is the most effective way to avoid the psychiatric risks of cannabis. In addition, they suggest delaying the use of cannabis as long as possible, and ideally until after adolescence.

Dr. Romina Mizrahi, MD, professor of psychiatry at the University of Toronto, and director of the Focus on Youth Psychosis Prevention program at CAMH explains:

“The key issue, I think, here really has to do with brain development,” she says. “One would want to minimize use before the brain is developed. And I would usually say ideally until 24 or 25. But I mean, it has to be after the age of 21, for sure.”

The guidelines also recommend people opt for cannabis with lower THC content overall, and a higher CBD to THC ratio.

Dr. Mizrahi emphatically agrees.

“We know that THC is associated with psychotic experiences, and we also know it’s associated with abuse and dependence. So certainly I want to make that recommendation that when people have to choose, they attempt as much as possible to use a minimal THC content.”

Finally, the guidelines suggest that people with a family history of psychosis should not consume cannabis at all.

If you have a first-degree relative—a mother, father, brother, sister, or child—who has experienced a psychotic disorder, it is worth being extra cautious.

Your risk is higher the more closely you are related to the affected individual. For example, the risk of schizophrenia is 6.3x higher in those with an affected first-degree relative, and 2.4x higher in those with an affected second-degree relative. Second-degree relatives include aunts, uncles, nieces, nephews, half siblings, grandparents, and grandchildren.

Dr. Kim Lam, MD, a patient educator at Apollo Cannabis Clinics in Toronto, has some additional advice to offer.



Cannabis with a higher CBD content and lower THC content can reduce harm in a mental health context. Dr. Kim Lam, Apollo Cannabis Clinics

Lam suggests patients with any history of mental illness use the “start low and go slow” rule. This means starting with a low dose of cannabis, and increasing it slowly to reduce the risk of side effects.

When asked about how cannabinoid content can impact a person’s experience, Lam’s clinical experience lines up with the CAMH guidelines.

“Cannabis with a higher CBD content and lower THC content can reduce harm in a mental health context,” Lam said.

“Because THC is psychoactive, and CBD has been shown to help diminish the side effects of THC, we often like to start patients on just CBD, and add THC only if needed.”

Importantly, people with mental health vulnerabilities who choose not to abstain from cannabis can still make choices to reduce the risk to their mental health.

Here are some harm reduction strategies for cannabis consumption:

Consider abstinence. Abstinence is the best way to avoid the mental health risks of cannabis consumption. Consider this more strongly if you have a close relative who is affected by psychosis.

Delay use until after adolescence (age 21). Cannabis is thought to affect teens’ brain development, which may account for some of the mental health risks.

If you choose to consume, select cannabis with lower THC content overall, and cannabis with a higher CBD to THC ratio. Avoid illicit cannabis, which is not tested.

Start low and go slow to reduce the risk of side effects. If you have a distressing mental experience while using cannabis, stop consuming it temporarily and seek help.

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Laura Tennant Laura Tennant is a Toronto freelance science writer. She has an Honours B.Sc. in Neuroscience from the University of Toronto. She hopes her writing will help others make better-informed choices about their health and lifestyle. View Laura Tennant's articles