Cannabis and Teen Mental Health: A Landmark New Study Every Parent Should Know About

For many international families moving to the Netherlands, one of the biggest cultural surprises is the country's reputation for being relaxed about cannabis. Teenagers quickly become aware of coffeeshops, and many come to believe that if cannabis is openly sold, it must be relatively harmless.

However, a major new study published in JAMA Health Forum reminds us that legal tolerance and health risk are two very different things.

The researchers followed 463,396 adolescents between the ages of 13 and 17 over several years, making this one of the largest and most comprehensive studies ever conducted on cannabis use and adolescent mental health. Unlike many earlier studies, which relied on small samples or focused only on cannabis dependence, this research looked at any self-reported cannabis use during the previous year and examined whether these young people later developed clinically diagnosed psychiatric disorders before the age of 26.

What did the researchers find?

The results were striking.

Compared with adolescents who did not report using cannabis, those who had used cannabis during the previous year were significantly more likely to later receive a diagnosis of:

• Psychotic disorders

• Bipolar disorder

• Depressive disorders

• Anxiety disorders

The strongest associations were seen for psychotic and bipolar disorders.

Teenagers who used cannabis had more than double the risk of developing a psychotic disorder later on. Their risk of developing bipolar disorder was also approximately twice as high.

Although the increased risks for depression and anxiety were smaller, they were still statistically significant and clinically meaningful.

One particularly important finding was that these associations remained even after researchers adjusted for many other factors known to influence mental health, including sex, ethnicity, neighbourhood deprivation, alcohol use and the use of other substances.

Even after taking previous psychiatric diagnoses into account, cannabis use continued to predict a higher likelihood of later mental health disorders.

Why is this study different?

Research on cannabis and mental health is not new, but this study stands out for several reasons.

First, the sheer size of the study gives its findings considerable weight. More than 463,000 adolescents were included, making it one of the largest longitudinal investigations ever conducted on this topic.

Second, the researchers followed young people over time. This is important because it allows them to examine whether cannabis use came before the development of psychiatric disorders rather than simply observing that the two occur together.

On average, cannabis use was reported 1,7 to 2,3 years before a psychiatric diagnosis was made. While this still does not prove that cannabis directly caused these disorders, it strengthens the argument that cannabis may contribute to their development in vulnerable young people.

Third, the researchers did not simply study adolescents with cannabis addiction. Even past-year cannabis use, regardless of frequency, was associated with increased risk. This suggests that the conversation should not only be about heavy or dependent use, but also about delaying experimentation during adolescence whenever possible.

Does cannabis cause mental illness?

This is probably the most important question—and also the one that requires the most careful answer.

The study does not prove causation.

Mental health develops through a complex interaction of genetics, brain development, family history, stress, trauma, personality and environmental influences. Some adolescents may already have subtle mental health difficulties that make them more likely to experiment with cannabis.

The researchers acknowledge this possibility. In fact, they specifically investigated it by adjusting for previous psychiatric conditions and conducting several additional analyses. Even after doing so, the increased risks remained.

This means the relationship is unlikely to be explained solely by pre-existing mental health problems.

The authors conclude that adolescent cannabis use is likely to be a contributing risk factor, particularly for severe disorders such as psychosis and bipolar disorder, rather than merely a consequence of existing symptoms.

Why are adolescents particularly vulnerable?

The teenage brain is still developing.

Brain regions responsible for planning, decision-making, emotional regulation and impulse control continue maturing well into the mid-twenties.

THC—the psychoactive component of cannabis—acts on the brain's endocannabinoid system, which plays an important role in normal brain development. Researchers believe that exposure during adolescence may interfere with these developmental processes, especially when cannabis use begins at a younger age or involves higher-potency products.

Interestingly, the study also found that the relationship between cannabis use and depression or anxiety was strongest in younger adolescents and became weaker as participants entered adulthood. This suggests that early adolescence may be a particularly sensitive period for the effects of cannabis.

What does this mean for families living in the Netherlands?

This is where many international parents become understandably confused.

The Netherlands has a global reputation for being permissive about cannabis. However, the reality is more nuanced.

Cannabis is not legal for children or adolescents under the age of 18. Coffeeshops are prohibited from selling cannabis to minors, advertising is tightly restricted, and Dutch healthcare professionals continue to advise delaying cannabis use for as long as possible because of the potential effects on the developing brain.

The Dutch system is best described as one of harm reduction, not endorsement. The aim is to reduce organised crime and regulate adult access while protecting young people from early exposure.

Unfortunately, teenagers do not always appreciate this distinction. Many hear only that "weed is legal in the Netherlands" and mistakenly conclude that it must therefore be safe.

This new study provides another reminder that legality and health risk are not the same thing.

What should parents take away from this research?

There is no reason for panic if your teenager has experimented with cannabis once or twice. Most young people who use cannabis will not develop a serious psychiatric disorder.

At the same time, the evidence is becoming increasingly consistent that the earlier cannabis use begins, the greater the potential risk.

Parents do not need to rely on scare tactics. Instead, honest conversations based on evidence are far more effective. Teenagers are often more receptive when parents acknowledge that cannabis is common while also explaining why the adolescent brain is uniquely vulnerable.

If your child already struggles with anxiety, low mood, ADHD, autism, emotional regulation difficulties or there is a family history of psychosis or bipolar disorder, discussing cannabis use becomes even more important.

Final thoughts

This landmark study adds to a growing body of research suggesting that adolescent cannabis use is associated with an increased risk of developing several psychiatric disorders later in adolescence and young adulthood. While no single study can prove cause and effect, the consistency, size and quality of this research make its findings difficult to ignore.

For international families raising children in the Netherlands, understanding both the science and the Dutch approach to cannabis is essential. The country's tolerance policy should not be mistaken for a message that cannabis is harmless for developing brains.

As child psychologists, our goal is not to create fear, but to empower families with evidence-based information.

Open conversations, accurate knowledge and delaying cannabis use for as long as possible remain some of the best ways to support healthy adolescent development.