Long-term cannabis use linked to subtle brain structure changes in key decision-making area

Cannabis is often perceived as relatively low risk. However, previous brain imaging studies have produced mixed findings, particularly in younger users. This new study focused specifically on adults with long-term, heavy use patterns to examine whether measurable structural differences are present.

Researchers conducted high-resolution magnetic resonance imaging scans in 46 adults who had used cannabis for at least 10 years and consumed it daily for at least five years. Their average age was 31.3 years. They were compared with 46 adults who had used cannabis fewer than 10 times in their lifetime, matched for age, sex and IQ.

The researchers examined three aspects of brain structure. Cortical thickness refers to the width of the brain's outer layer. Surface area and cortical volume are additional measures of brain structure that reflect overall size and shape. The authors examined the volume of subcortical nuclei, including the basal ganglia and hippocampus.

Key findings include:

• Two areas of reduced cortical thickness were identified in the right rostral middle frontal cortex in long-term heavy cannabis users
• After controlling for potential confounders by adjusting for standard drink units and excluding recent, sporadic cocaine users, the reduction in right rostral middle frontal cortical thickness remained significant, although only one cluster was observed
• This region forms part of the prefrontal cortex, which plays a central role in executive functions such as planning, working memory and impulse control
• No significant differences were observed between users and non-users in overall cortical volume
• No significant differences were observed in cortical surface area

The findings suggest that long-term heavy cannabis use may be linked to subtle and region-specific cortical thinning, rather than widespread changes.

A. Aquino-Servin, Lead Author, FIDMAG Germanes Hospital&ries Research Foundation, said: "We found reduced thickness in a frontal brain region that supports executive functioning. While this study does not establish cause and effect, it adds to growing evidence that sustained heavy cannabis use may be associated with structural brain differences."

Dr. Julian Beezhold, the Secretary General of the European Psychiatric Association, said: "As cannabis policies and public attitudes evolve, robust imaging studies like this are important for informing public health discussions with objective data."