Spanish scientists have identified significant structural brain changes in chronic cannabis users that impair motivation and decision-making capabilities, findings that arrive as campaigners push for legalisation across Britain.
The study, presented at the European Congress of Psychiatry in Prague, discovered that individuals who smoked cannabis daily for a minimum of five years exhibited measurable thinning in the right rostral middle frontal cortex—a brain region governing high-level planning and executive function.
Researchers from Fidmag Germanes Hospitalàries Research Foundation examined 46 adults averaging 31 years old who had consumed cannabis for approximately a decade, comparing their MRI scans against an equivalent cohort who had used the substance fewer than ten times during their lives.
Lead author Ana Aquino-Servin explained the cortical thinning could signify loss or shrinkage of critical brain cells, or reduced connectivity between neurons in areas essential for complex cognitive processes.
“Executive functions are really complex processes and it includes planning, decision making, working memory,” Ms Aquino-Servin told The Times. “They are processes that we need every day to deal with daily problems.”
She suggested regular heavy users might struggle with task initiation and productivity, noting: “Maybe they don’t have a big struggle to do [tasks], but maybe the brain needs to do more work to do it. I think another issue that can be going on here is the relation between [cannabis] use and a decrease of motivation.”
The findings carry particular relevance as Green Party leader Zack Polanski campaigns for cannabis legalisation, arguing regulated markets would generate tax revenue whilst improving oversight.
However, scientists emphasised additional research is required to establish whether the observed changes prove permanent or reversible following cessation, and to definitively confirm cannabis as the causal factor.
Dr Julian Beezhold, secretary general of the European Psychiatric Association, stated: “As cannabis policies and public attitudes evolve, robust imaging studies like this are important for informing public health discussions with objective data.”
Previous investigations have documented cannabis effects on adolescent and young adult frontal lobes, though this represents among the first studies reporting structural differences linked to sustained adult usage.
Researchers attribute the frontal cortex’s vulnerability to the high concentration of CB1 receptors in this region, which bind to cannabis’s primary psychoactive compound to produce intoxication effects.
Cannabis remains legally prescribable in Britain for certain medical conditions, whilst recreational users frequently perceive the substance as low-risk or benign. The Spanish team’s findings suggest this perception may underestimate long-term cognitive consequences.
