Drug lobbyists and marijuana producers promote it as a safe means of solving a number of health problems — including anxiety, depression, pain, and sleep disorders. However, as the latest detailed studies have shown, even rare use of cannabis is associated with an increased risk of mental disorders, and in young people — with poorer development of memory, cognitive abilities, and the ability to control their behavior and emotions.
Illustrative image. Photo: freepik.com
Marijuana is a narcotic substance obtained from dried parts of the hemp plant. Its psychoactive effect is due not to alkaloids, but to cannabinoids — chemical compounds that affect the brain. The main one is tetrahydrocannabinol (THC), which alters consciousness, mood, and perception. In total, more than 500 chemical compounds have been identified in hemp, including over 100 cannabinoids.
The geography of marijuana legalization is expanding every year, and some companies are promoting it almost as a general wellness product — similar to vitamin supplements. In the USA, according to data from the Substance Abuse and Mental Health Services Administration for 2024, the largest increase in use is observed among people over 60 years old. This is often associated with medical use — for example, for pain, arthritis, sleep problems, or anxiety conditions.
At the same time, scientific data show that regular marijuana use is associated with impaired cognitive functions. In a study published in 2025 in the journal JAMA Network Open, scientists analyzed over a thousand adults using neuroimaging. People who consistently used marijuana showed lower brain activity during working memory tasks compared to those who did not use it.
Long-term use is also associated with structural changes in the brain, including changes in its volume. These effects are more pronounced in people who started using marijuana in adolescence when the brain is still forming.
Separate studies show changes in the brain's white matter in those who started using before the age of 16. White matter provides connections between different parts of the brain, so its impairments can affect executive functions — the ability to control behavior, make decisions, and restrain impulses. In young users, this often manifests as greater impulsivity and difficulties with complex cognitive tasks.
In a meta-analysis of dozens of studies, published in the journal Addiction, marijuana use was also linked to changes in brain structures, particularly in the amygdala — an area involved in processing emotions.
Researchers pay special attention to adolescents. A large-scale study by the University of California, San Diego, involving about 11,000 adolescents, found that marijuana users had poorer brain development indicators. They showed weaker results in verbal memory, lower information processing speed, poorer cognitive control, as well as problems with working memory and spatial skills.
The researchers considered a number of factors — socio-demographic conditions, family history of addictions, use of other substances, and even prenatal exposure. This allowed for maximum reduction of the influence of confounding factors on the results, although it is impossible to completely exclude them in such studies.
Interestingly, in their early years, future marijuana users often even outperformed their peers in certain cognitive indicators. However, with age and increasing intensity of use, their development slowed down, while that of other adolescents continued.
As scientists explain, the young person's brain is particularly vulnerable because it continues to form until approximately 25 years of age. THC can influence the development of systems responsible for decision-making, emotion regulation, and reward mechanisms.
New studies also show that even episodic marijuana use during adolescence — for example, once a month or less — is associated with an increased risk of mental disorders and poorer academic outcomes. It is important to note that this refers to a statistical correlation, which does not necessarily imply a direct cause-and-effect relationship.
In a study involving more than 460,000 adolescents aged 13–17, those who used marijuana in the past year more frequently reported symptoms of depression, anxiety disorders, psychosis, and bipolar disorder.
"We do not find a level of marijuana use in adolescents where negative effects would not be observed," notes psychiatrist Ryan Sultan from Columbia University in an interview with The Wall Street Journal.
Furthermore, initiating use before the age of 18 significantly increases the risk of developing addiction. The situation is complicated by the fact that modern products can contain very high concentrations of THC — up to 90%, whereas in natural forms of hemp, its level usually constitutes a few percent.
Against this background, the image of marijuana as a "safe" or even beneficial substance appears increasingly unconvincing. Science currently provides no grounds to consider it risk-free — especially when it comes to adolescents, for whom even episodic use can have long-term consequences for brain and mental health.
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