Cannabis Adolescent Mental Health

While cannabis use is prevalent and may be perceived as harmless by some, especially among adolescents, it’s essential to recognise the potential risks it poses to mental health. A review at McGill University from 2019 suggests that using cannabis during adolescence can lead to a higher likelihood of depression and other mental health issues in young adulthood. It’s vital to stay informed and make informed choices when it comes to substance use, especially during the formative years of adolescence. If you or someone you know is struggling with mental health issues related to cannabis use, seeking professional help and support is essential.

Cannabis is a widely used drug around the world, with millions of people trying it at some point in their lives. However, what many people may not know is that using cannabis, especially during adolescence, can have significant effects on mental health.

Cannabis Use on the Rise

Cannabis is the most commonly used illicit drug globally. Approximately 3.8% of people worldwide have used cannabis within the past year. While overall usage rates have remained fairly stable since the 1990s, the patterns within specific countries have changed. For example, the number of young adults in the United States using cannabis nearly doubled between 2001 and 2013. In Australia, 4% of adolescents aged 14 to 19 years use cannabis weekly.

The active component in cannabis responsible for most of its psychoactive effects is Δ-9 tetrahydrocannabinol (THC), which is responsible for the “high”.

Adolescent Cannabis Use and Mental Health

  • Using cannabis during adolescence can result in several harmful consequences, including:
  • Diminished scholastic achievement.
  • Lower degree attainment and school dropout rates.
  • Earlier onset of psychosis.
  • Neuropsychological decline.
  • Increased risk of motor vehicle accidents.
  • Higher chances of developing psychoses, particularly among frequent and high-potency users.
  • Increased likelihood of progressing to problematic cannabis use.
  • Adverse birth outcomes when mothers smoke cannabis during pregnancy.
  • Worsened respiratory symptoms and more frequent episodes of chronic bronchitis with long-term use.

Depression and Mood Disorders

The analysis demonstrates that using cannabis during adolescence is linked to a higher risk of developing major depression during young adulthood. This finding is particularly concerning, given that major depressive disorder is a debilitating mental illness associated with increased suffering, a higher mortality rate, and greater disability among those affected.

Modest Effect Size but Major Implications

The effect size of the association between adolescent cannabis use and depression is described as modest. However, if we consider that in Australia 4% of adolescents use cannabis weekly, the consequences are even more important. The study estimated that about 7.2% of young adult depression cases may be potentially linked to cannabis exposure. This translates to approximately 413,326 young adults in the United States who could experience depression due to cannabis use.

Impact on Brain Development

One key reason for this connection lies in the impact of cannabis on the developing brain. The human brain undergoes critical development from prenatal stages through childhood and adolescence until around the age of 21. During this time, it is particularly vulnerable to the long-term effects of environmental factors, including exposure to THC (the active component in cannabis). Studies have shown that earlier and higher-dose cannabis use can lead to neuroanatomic alterations in brain regions, particularly those with a high concentration of cannabinoid receptors.

Cannabis use during adolescence can result in changes in brain structure, including decreased volume in areas like the hippocampus, amygdala, and prefrontal cortex. Additionally, it can lead to greater grey matter density in specific brain regions. Animal studies have shown that adolescent cannabis exposure can cause an increase in anhedonia (a reduced ability to experience pleasure) and anxiety in adulthood, linked to changes in neurotransmitters like serotonin and norepinephrine. There is also evidence of reduced responsiveness to cannabinoids in dopamine neurons, potentially contributing to long-lasting cross-tolerance to other substances like morphine, cocaine, and amphetamine.


The analysis underscores the importance of understanding the potential risks associated with adolescent cannabis use. It highlights a clear connection between such use and an increased risk of major depression in young adulthood. These findings emphasise the need for informed decision-making regarding cannabis use, particularly during the crucial stages of brain development in adolescence. If you or someone you know is struggling with depression or other mental health issues related to cannabis use, seeking professional help and support is essential.

Please note that this blog post by Personal Psychology is not intended to provide professional advice. If you or someone you know is experiencing mental health difficulties, it is important to seek help from a qualified healthcare professional.