What the evidence shows about marijuana and teen mental health

But what does the evidence actually tell us about its impact on mental health?

A recent scoping review led by researchers from Torrens University Australia examined the relationship between cannabis use and mental health among young people in Australia and the United States. The review analysed evidence from 24 studies involving hundreds of thousands of adolescents and young adults to better understand the potential risks associated with cannabis use.

The findings paint a complex picture. While cannabis use does not affect every young person in the same way, the evidence suggests that frequent and early use is associated with a range of adverse mental health outcomes.

Depression and psychological distress

One of the strongest findings from the review was the association between cannabis use and depression. Across multiple studies, young people who used cannabis were more likely to experience depressive symptoms than non-users, particularly when use began during adolescence or occurred regularly over time.

The review also found that the relationship may be more pronounced among vulnerable groups, including LGBTQI youth and some minority populations. While researchers cannot conclude that cannabis directly causes depression in every case, the evidence consistently shows a significant association between the two.

Suicide risk cannot be ignored

Several studies included in the review reported higher rates of suicidal thoughts, suicide planning and suicide attempts among young cannabis users. One large meta-analysis found that adolescents who used cannabis were significantly more likely to report suicidal ideation and were more than three times as likely to attempt suicide compared with non-users.

These findings do not mean that cannabis causes suicidal behaviour on its own. Mental health is influenced by many social, psychological and environmental factors. However, the review highlights

Psychosis and cognitive effects

The review identified evidence linking cannabis use with psychotic symptoms, including hallucinations and paranoia, particularly among frequent users and those experiencing cannabis use disorder. Young people who used cannabis more frequently appeared to face greater risks.

Researchers also found evidence of cognitive impacts. One meta-analysis reported a modest decline in IQ among young people who regularly used cannabis. Although the average decrease was small, it raises important questions about how cannabis exposure may affect the developing adolescent brain.

Cannabis use disorder and dependence

Contrary to the common perception that cannabis is non-addictive, the review found substantial evidence for cannabis use disorder among young people. Risk increased as frequency and intensity of use increased, with heavy users experiencing the highest rates of dependence and associated mental health problems.

Young people with cannabis use disorder were also more likely to experience co-occurring mental health conditions and other substance use problems.

Some young people face greater risks

The review found that mental health risks were not evenly distributed across all young people. Groups identified as potentially more vulnerable included:

• Aboriginal and Torres Strait Islander youth
• LGBTQI young people
• Young people who begin using cannabis at an earlier age
• Frequent or long-term cannabis users
• Young women, who appeared more susceptible to some mental health impacts than males

These findings highlight the importance of targeted prevention and support strategies for populations that may already experience social, health or structural disadvantages.

What about anxiety?

Interestingly, the evidence regarding anxiety was less clear. Some studies found an association between cannabis use and anxiety symptoms, while others found no statistically significant relationship. The researchers concluded that more high-quality longitudinal research is needed to better understand this connection.

What should parents, teachers and communities take away?

The review does not suggest that every young person who uses cannabis will experience mental health problems. However, it does highlight the importance of informed decision-making and early intervention.

For parents and caregivers, open and non-judgmental conversations about substance use can be more effective than fear-based messaging.

For teachers and schools, education programs that provide accurate information about cannabis use and mental health can help students make informed choices.

For communities and policymakers, the findings reinforce the need for evidence-based public health strategies that support prevention, early identification and access to mental health services.

From student project to published research

The review began as a Master of Public Health Capstone project at Torrens University Australia and evolved into a peer-reviewed publication. Led by student researcher (now alumnus) Aayush Baral under the supervision of Associate Professor Fahad Hanna, the project demonstrates how student research can contribute to important public health conversations and generate evidence that informs practice, policy and community awareness.

As discussions about cannabis legalisation and social acceptance continue, understanding the evidence is more important than ever. This review reminds us that while perceptions may be changing, the mental health implications for young people deserve careful thought.

Research: Cannabis Use and Its Impact on Mental Health in Youth in Australia and the United States: A Scoping Review, published in Epidemiologia (2024).