Heavy Cannabis Use Was Linked to Thinning of a Brain Region Involved in Decision-Making Over Three Years | Research

The takeaway

Young adults who used cannabis heavily showed significant thinning of the left orbitofrontal cortex over three years, and greater thinning correlated with more severe cannabis use disorder symptoms.

Young adults who use cannabis heavily, parents, and anyone interested in the long-term brain effects of regular cannabis use.

Left orbitofrontal cortex thinning correlated with cannabis use disorder severity at 3-year follow-up

What the researchers found

At three-year follow-up, heavy cannabis users showed significant cortical thinning in the left lateral orbitofrontal cortex compared to both their own baseline and control subjects. The degree of thinning correlated positively with scores on a cannabis use disorder screening tool, suggesting a dose-response relationship.

Why it matters

The orbitofrontal cortex is critical for decision-making, impulse control, and emotional processing. Thinning in this area could help explain why heavy cannabis use is associated with difficulty controlling use and making decisions about continued consumption.

The numbers in context

Significant cortical thinning in the left lateral orbitofrontal cortex at 3-year follow-up in heavy users. Time effects showed changes in bilateral medial frontal cortex, bilateral posterior cingulate cortex, and bilateral insula. Positive correlation between Cannabis Use Disorders Identification Test scores and OFC thickness at follow-up.

How the study worked

Longitudinal study comparing cortical thickness changes from baseline to three-year follow-up in young adults with heavy cannabis use versus controls. Brain imaging measured cortical thickness across multiple regions. Cannabis use severity was assessed using the Cannabis Use Disorders Identification Test.

What this study cannot tell us

Cannot definitively rule out that pre-existing brain differences led to heavier cannabis use rather than the reverse. Sample sizes were not reported in the abstract. Other substance use and lifestyle factors could contribute to cortical changes.

How to read the evidence

Moderate: longitudinal design with objective brain imaging and dose-response relationship, though limited by potential confounders and unmeasured variables.

When this study was published

2025 study.

The bigger picture

This is one of few longitudinal studies tracking actual brain structural changes in heavy cannabis users over time, rather than just comparing users to non-users at a single point. The finding that changes correlate with use severity strengthens the case for a biological link.

Questions still open

Are these cortical changes reversible with cannabis cessation? Do they translate to measurable cognitive decline in everyday functioning? At what level of use do these changes begin to appear?

Common questions

What does the orbitofrontal cortex do?

It plays key roles in decision-making, impulse control, and emotional processing. Changes in this region could affect the ability to weigh consequences and regulate behavior.

Does this prove cannabis causes brain thinning?

The longitudinal design strengthens the case, but it cannot completely rule out that pre-existing differences contributed. The correlation between use severity and thinning does support a biological relationship.

Read the original research

Abnormal Cortical Thickness Development in Young Adults With Heavy Cannabis Use: A Longitudinal Study.

Addiction biology, 30(5), e70040

View on PubMed ↗Publisher’s paper ↗

Citation

Li, Wei; Xu, Cheng; Xu, Hanyuan; Yin, Bo; Xu, Hui; Li, Dandong. (2025). Abnormal Cortical Thickness Development in Young Adults With Heavy Cannabis Use: A Longitudinal Study.. Addiction biology, 30(5), e70040. https://doi.org/10.1111/adb.70040