Winter 2019

What You Need to Know About Cannabis Use and the Developing Brain

With the federal government legalization of cannabis on October 17, 2018, many medical associations, mental health organizations, community groups, law enforcement agencies and educational bodies have expressed grave and deep concerns about what the public does notknow about cannabis and the very paramount importance of safeguarding the mental wellness of youth and young adults.

So why such grave and deep concern? One concern which this article focuses on is the affect of cannabis on the developing brain. Listen to some of the experts: 

“There is a strong evidence-base showing that early and regular cannabis use can affect cognition, such as memory, attention, intelligence and the ability to process thoughts and experiences.”
Dr. Renuka Prasad, President of the Canadian Psychiatric Association.

 “Cannabis with high tetrahydrocannabinol (THC) content can result in significantly worse mental health and cognitive outcomes, including worsening of panic disorder and other anxiety disorders.”
Dr. Phil Tibbo, Chair of the Canadian Consortium for Early Intervention in Psychosis.

“We now have international data that support the fact that cannabis is a risk factor for psychosis for some, though not all, patients with schizophrenia, and those patients with a positive cannabis history need help to understand the negative effect of cannabis on psychosis.”
Dr. Elsie-Marie Løberg, University of Bergen in Norway. 

“The link between using pot and developing serious mental illness is strongest in the youngest smokers – 12- to 15-year-olds, or kids even younger.”
Dr. Matthew Large, University of New South Wales in Sydney, Australia. 

“Simply put, cannabis should not be used by young people. It is toxic to their cortical neuronal networks, with both functional and structural changes seen in the brains of youth who use cannabis regularly.”
Diane Kelsall, Interim Editor-in-Chief of the Canadian Medical Association Journal.

The Canadian Paediatric Society cautions that marijuana use in youth is strongly linked to “cannabis dependence and other substance use disorders; the initiation and maintenance of tobacco smoking; an increased presence of mental illness, including depression, anxiety and psychosis; impaired neurological development and cognitive decline; and diminished school performance and lifetime achievement.”

The bottom line is that the “endocannabinoid system” is involved in brain development, even during the adolescent time period where the ‘fine tuning’ occurs. The cannabinoid receptors for this system are primarily on white matter in adolescents and not in their adult configuration (more on grey matter) until adulthood. This is why cannabis can have a different effect on the brain developmentally in adolescents than in adulthood.

Dr. Candice Crocker of the Nova Scotia Early Psychosis Program and Dr. Phil Tibbo, Chair of the Canadian Consortium for Early Intervention in Psychosis state:

1. Cannabis use can contribute to the development of psychosis.

Regular cannabis use, particularly in early adolescence and with high THC content strains, is associated with an increased risk of developing psychosis and schizophrenia. Regular adolescent use also lowers the age of onset. This risk is potentially increased in vulnerable youth

2. Cannabis use may worsen symptoms of depression.

While there is a smaller body of literature compared to cannabis and psychosis investigations, cannabis use has been positively associated with symptoms of depression. A recent metanalysis reported an increased risk of depression following heavy cannabis use starting at early ages. Adolescent use may also increase the risk of suicide. 

3. Cannabis use can worsen symptoms of anxiety.

A positive association has been found between anxiety disorders and cannabis use in the general population. In particular, longitudinal research which adjusted for substance use, education, and family situation has found that adolescent cannabis use was associated with anxiety in young adulthood.

4. Regular use of cannabis can impair cognitive function.

Neuropsychological research report that regular cannabis use in adolescence can impair working memory, visual scanning, learning and cognitive flexibility. Improvement in some of these domains on cessation may occur, but not all.

5. Cannabis use can affect brain development

Cannabis, thru its effects on the endocannabinoid system, may alter brain structure and function during the adolescent phase of brain development. This can affect both grey and white matter structures, including reported changes in cortical thickness and hippocampal volumes that may not be reversible in individuals who began use prior to the age of 16.

The human brain continues to develop until around the age of 25. Use of cannabis prior to that age can negatively affect the brain’s healthy maturation process. That’s why many professionals advocated prior to legalization that legal access to cannabis be restricted to age 21 and over, and that legislation should restrict the quantity and potency of the drug until age 25. 

What’s importantly needed now is: (1) public education targeting youth and young adults about the effects early cannabis use can have on brain development; (2) further research to better understand the impact of cannabis and its legalization on mental health and; (3) expanded support for prevention, early identification and cannabis cessation treatments within the framework of mental health and addictions. 

I am often asked, “Who is the person at greatest risk.” The younger the age, the frequency of use, and the potency of the cannabis, that person is at a greater risk. If mental illness is in the family history, the risk increases 5 to 7 fold that the person will develop cannabis induced psychosis which then may lead to life-long schizophrenia. The Schizophrenia Society of Canada has produced as a youth participatory project geared towards youth. Another great resource is

Dr. Christopher Laine Summerville B.A., M.Div., M. Miss., D. Min. CPRRP, LL.D (Honoris Causa) Since 1995 Chris has been the Executive Director of the Manitoba Schizophrenia Society, providing leadership and supervision to a team of 17 located in the home office in Winnipeg and the eight regional outreach offices throughout Manitoba. Since 2007 Chris has also served as CEO of the Schizophrenia Society of Canada.

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