Heavy Cannabis Use Did Not Impair Basic Motor Function on Brain Scans | Research

The takeaway

BOLD-fMRI brain scans showed no significant differences in motor cortex activation between heavy cannabis users (15 joints/day), moderate users, and light users, suggesting motor function is preserved despite chronic use.

Neuroscience researchers, people concerned about cannabis effects on brain function

No motor function differences found between users consuming 15 joints/day and non-users

What the researchers found

Three groups of cannabis users (heavy: 15 joints/day, moderate: 1.5 joints/day, light: 2.8 joints/week) plus healthy controls showed no significant differences in motor cortex activation patterns during fMRI-assessed motor tasks. Brain plasticity and reorganization of motor control appeared equivalent across all groups.

Why it matters

While cannabis is known to affect cognition and memory, this study suggests that basic motor cortex function may be resilient to chronic use, even at very high consumption levels. This distinction between preserved and impaired brain functions could inform understanding of cannabis effects on the brain.

The numbers in context

23 cannabis users in 3 groups: 11 heavy (15 joints/day), 6 moderate (1.5 joints/day), 6 light (2.8 joints/week); 6 healthy controls; no significant differences in BOLD-fMRI motor activation across groups

How the study worked

23 cannabis users divided into three consumption groups plus 6 healthy controls underwent BOLD-fMRI assessments of motor function, along with neuropsychological and biological assessments.

What this study cannot tell us

Very small sample sizes per group (6-11 participants), cross-sectional design cannot rule out pre-existing differences, only motor function tested, no control for acute intoxication at time of scan, limited to cortical motor areas

How to read the evidence

Very small study (29 total participants) with limited statistical power; interesting null finding but sample too small for confident conclusions

When this study was published

Published 2025

The bigger picture

Understanding which brain functions are affected by chronic cannabis use and which are preserved helps build a more nuanced picture than the common assumption that cannabis broadly impairs brain function.

Questions still open

Would more sensitive motor tasks reveal subtle differences? Are other motor-related brain areas (cerebellum, basal ganglia) affected even if primary motor cortex is not? Does preserved motor function extend to fine motor skills and coordination?

Common questions

Does chronic cannabis use affect motor function?

In this small fMRI study, even heavy cannabis users (15 joints/day) showed no significant differences in motor cortex activation compared to non-users, suggesting basic motor control may be preserved despite heavy use.

How should this null finding be interpreted?

With only 29 total participants in 4 groups, the study may simply lack the statistical power to detect real differences. The finding is suggestive but needs replication in larger samples.

Read the original research

Heavy and Chronic Cannabis Addiction does not Impact Motor Function: A BOLD-fMRI Study.

CNS & neurological disorders drug targets, 24(6), 475-490

View on PubMed ↗Publisher’s paper ↗

Citation

Boujraf, Saïd; Alami, Badreeddine; Chikri, Mohamed; El Hamdaoui, Halima; Maaroufi, Mustapha; Aalouane, Rachid; Rammouz, Ismail. (2025). Heavy and Chronic Cannabis Addiction does not Impact Motor Function: A BOLD-fMRI Study.. CNS & neurological disorders drug targets, 24(6), 475-490. https://doi.org/10.2174/1574886317666220516103501