Cannabis Use in Young Adults Tied to Lower Attention

Cannabis has become increasingly accepted for both medical and recreational use, but emerging research suggests that when cannabis is used may be just as important as why it is used. A 2026 longitudinal study¹ followed hundreds of young adults over several years and uncovered a noteworthy pattern: those whose cannabis use increased during the transition into adulthood tended to perform worse on measures of attention while also reporting higher levels of anxiety, depression, and ADHD symptoms.

The findings do not suggest that cannabis is inherently harmful or that every young adult who consumes it will experience cognitive problems. Instead, they highlight an important reality about brain development, as emerging adulthood is one of the final stages of brain maturation. At the same time, the researchers caution that the relationship is likely more complex than simple cause and effect. Understanding both sides of this relationship is essential for making informed decisions about cannabis use.

Why Emerging Adulthood Matters

The years between approximately ages 18 and 25 are often called emerging adulthood. During this period, the brain continues refining important networks involved in attention, decision-making, emotional regulation, and impulse control. Although many people assume brain development is complete after the teenage years, neuroscience shows that several regions, particularly the prefrontal cortex, continue to mature well into the mid-twenties. Because of this ongoing development, researchers have long wondered whether increasing substance use during this period might influence cognitive function later.

Previous studies have suggested a possible connection, but many relied on self-reported cannabis use, making it difficult to accurately measure exposure over time. However, this new research took a different approach by objectively measuring substance use through biological testing.

How the Study Was Conducted

Researchers followed 731 young adults participating in an ongoing Swiss longitudinal study. Instead of relying solely on participant questionnaires, investigators analyzed hair samples collected when participants were approximately 20 years old and again at age 24. Hair testing allowed researchers to objectively detect more than 100 psychoactive substances and their metabolites over an extended period, providing a much clearer picture of changing substance use patterns.

The researchers then grouped participants according to how their substance use changed over the four-year period. Five distinct patterns emerged among those who used substances:

• Individuals whose substance use remained low or decreased.
• Those whose cannabis use increased.
• Those whose club drug use increased.
• Those whose prescribed stimulant use increased.
• Those whose prescribed sedative use increased.

Participants also completed standardized assessments of attention, working memory, declarative memory, overall cognitive performance, and mental health symptoms including anxiety, depression, and ADHD. This combination of objective biological testing and long-term follow-up makes the study stronger than many previous investigations examining cannabis and cognition.

Cannabis Increases Were Linked to Lower Attention

Participants whose cannabis use increased showed a consistent pattern involving attention. Compared with participants who showed no detectable substance use in their hair samples, cannabis increasers demonstrated modest but measurable reductions in attention performance.

Attention plays a central role in everyday functioning. It influences learning, workplace performance, driving, multitasking, and the ability to stay focused during conversations or complex tasks. Even relatively small reductions can become meaningful over time, particularly in educational or professional settings.

Mental Health Symptoms Also Increased

The study also found that participants whose cannabis use increased reported higher levels of anxiety, depression, and ADHD symptoms by age 24. Mental health is influenced by countless factors, including genetics, environment, stress, trauma, sleep, social support, and existing psychiatric conditions, making cannabis one piece of a much larger picture. However, the findings reinforce previous research suggesting that heavier or increasing cannabis use during adolescence and early adulthood often occurs alongside worsening emotional well-being in some individuals.

For healthcare providers, this means that increasing cannabis use may sometimes serve as a signal to explore underlying mental health concerns rather than focusing exclusively on the cannabis itself.

The Relationship May Go Both Ways

One of the most important messages to take away from this research is that the relationship between cannabis and mental health is likely bidirectional. On one hand, increasing cannabis use during a period of ongoing brain development may contribute to subtle changes in attention and emotional health. On the other hand, young adults who are already experiencing anxiety, depression, ADHD symptoms, or difficulties concentrating may be more likely to use cannabis in an attempt to manage those symptoms.

This concept, known as self-medication, has been discussed in mental health research for decades. Many individuals report using cannabis because it temporarily reduces anxiety, improves sleep, quiets racing thoughts, or provides emotional relief. While some people perceive short-term benefits, self-medicating can sometimes make it harder to identify or properly treat the underlying condition. As a result, both directions of influence are likely occurring simultaneously rather than one completely explaining the other.

What This Means for Medical Cannabis

These findings should not be interpreted as evidence that cannabis lacks medical value. Cannabis and cannabinoid-based medicines have demonstrated therapeutic potential for conditions such as chronic pain, chemotherapy-induced nausea, multiple sclerosis-related spasticity, certain forms of epilepsy, and countless other medical conditions when used appropriately under medical supervision.

However, medical use typically differs substantially from recreational use. Medical treatment often involves carefully selected cannabinoid profiles, individualized dosing, physician oversight, and treatment of clearly defined health conditions. The current study primarily reflects patterns of increasing substance use among young adults rather than medically supervised cannabis therapy.

The Takeaway for Young Adults

This study adds to growing evidence that the timing of cannabis use matters. For individuals whose brains are still developing, increasing cannabis use during emerging adulthood may coincide with reductions in attention and higher levels of anxiety, depression, and ADHD symptoms. At the same time, those very symptoms may also encourage greater cannabis use, making the relationship more complicated than a simple cause-and-effect explanation.

The bottom line is not that cannabis is inherently harmful or should be viewed as universally dangerous. Rather, the findings support an increasingly consistent message from neuroscience that the fully mature adult brain appears better equipped to handle cannabis exposure than the developing brain.

As research continues, one recommendation remains remarkably consistent across both medical and recreational discussions: if cannabis is going to be used, waiting until the brain has largely completed its development may be one of the best ways to reduce potential risks while preserving its potential benefits.

References:

^{1. Eggenberger L., Janousch C., Johnson-Ferguson L., Baumgartner M.R., Binz T.M., Ribeaud D., Eisner M., Shanahan L. & Quednow B.B., Changing patterns of recent substance use in emerging adulthood and their associations with cognitive functions and mental health, Biological Psychiatry Global Open Science (2026), doi: https://doi.org/10.1016/j.bpsgos.2026.100795}