Frank Okon

Long-term cannabis use may alter brain structure and affect motivation and decision-making, according to new research presented at a major European psychiatry conference.

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The study, conducted by scientists at the Fidmag Germanes Hospitalàries Research Foundation, found that prolonged and heavy cannabis use is associated with thinning in a key part of the brain responsible for high-level thinking.

Cannabis, while legally prescribed in United Kingdom for certain medical conditions, is often regarded by recreational users as relatively low-risk. However, the findings add to growing evidence suggesting potential long-term effects on brain function.

Researchers focused on the frontal cortex, an area critical for executive functions such as planning, decision-making, and working memory. According to the study, extended cannabis use may lead to thinning in this region—potentially reflecting a loss of brain cells or reduced connectivity between them.

Lead author Ana Aquino-Servin said these structural changes could make it harder for regular users to engage in complex mental tasks.

“Executive functions are really complex processes and include planning, decision making, and working memory,” she explained. “They are processes that we need every day to deal with daily problems.”

She added that while users may still complete tasks, their brains might have to work harder to do so, potentially affecting productivity. The research also points to a possible link between cannabis use and reduced motivation, which could further impact an individual’s ability to initiate and sustain activities.

The study was presented at the European Congress of Psychiatry in Prague and involved 46 adults with an average age of 31. Participants reported daily cannabis use for at least five years, with overall use spanning roughly a decade.

Their brain scans were compared with those of a control group who had used cannabis fewer than ten times in their lives. The analysis revealed noticeable thinning in the right rostral middle frontal cortex among long-term users.

While earlier studies have linked cannabis use to changes in the frontal lobe among adolescents and young adults, researchers say this is among the first to identify structural differences tied specifically to long-term daily use in adults.

Scientists believe the effect may be linked to CB1 receptors, which are abundant in the frontal cortex. These receptors interact with the psychoactive compounds in cannabis that produce its characteristic “high,” potentially making this brain region more vulnerable to prolonged exposure.

Despite the findings, researchers caution that more work is needed to determine whether the observed changes are permanent or reversible after stopping cannabis use. They also note that the study does not definitively prove causation.

The research comes amid ongoing debates over cannabis policy. Advocates such as Zack Polanski have argued for legalization, citing potential benefits such as regulation and tax revenue.

However, experts say studies like this highlight the need for a clearer understanding of long-term health impacts before further policy shifts are made.

Julian Beezhold, secretary general of the European Psychiatric Association, said robust scientific evidence will be essential as attitudes toward cannabis continue to evolve.

“As cannabis policies and public attitudes evolve, studies like this are important for informing public health discussions with objective data,” he said.

The findings add a new dimension to the conversation around cannabis use, suggesting that while the drug may be perceived as relatively harmless, its long-term effects on the brain may be more complex.