Using transcranial magnetic stimulation, cannabis users showed increased cortical excitability and reduced intracortical inhibition compared to controls, with lower resting motor thresholds correlating with addiction severity.
Neuroscience researchers, neurologists, addiction specialists
Motor threshold correlated with addiction severity (p = 0.026)
What the researchers found
Cannabis users (n = 16) showed significantly higher motor evoked potential amplitude at 130% of resting motor threshold (p = 0.012), delayed cortical silent period onset at multiple intensities, and reduced short-latency intracortical inhibition at 4 ms interstimulus interval (p = 0.028). Resting motor threshold correlated negatively with addiction severity (p = 0.026).
Why it matters
This is direct neurophysiological evidence that cannabis use alters the balance between excitation and inhibition in the brain. The correlation between motor threshold and addiction severity suggests these changes track with heavier use.
The numbers in context
16 cannabis users vs. 20 controls; MEP amplitude increased (p = 0.012); CSP onset delayed (p = 0.018-0.036); SICI reduced at ISI 4 ms (p = 0.028); RMT correlated with addiction severity (p = 0.026).
How the study worked
Case-control study comparing 16 cannabis users and 20 controls using transcranial magnetic stimulation (TMS) measures of cortical excitability and inhibition, alongside clinical assessments including SCL-90-R, MoCA, and Hamilton anxiety/depression scales.
What this study cannot tell us
Very small sample (16 vs. 20). Cross-sectional design cannot determine whether cannabis caused the changes or whether people with different baseline excitability are more drawn to cannabis. No information on duration or amount of use.
How to read the evidence
Small case-control study with objective neurophysiological measures but very limited sample size.
When this study was published
2025 publication
The bigger picture
Altered cortical excitability could help explain cognitive and motor effects reported by cannabis users. If cannabis shifts the brain toward greater excitability with less inhibition, this may have implications for seizure threshold, impulsivity, and other neurological outcomes.
Questions still open
- Do cortical excitability changes reverse after cannabis cessation?
- Are these TMS changes related to functional cognitive or behavioral outcomes?
Common questions
Does cannabis change brain excitability?
What does increased cortical excitability mean?
Read the original research
The impact of cannabis use on cortical excitability and inhibitory mechanisms: A case-control study.
Psychiatry research, 351, 116617
Citation
Khedr, Eman M; Elserogy, Yasser; Ahmed, Gellan K. (2025). The impact of cannabis use on cortical excitability and inhibitory mechanisms: A case-control study.. Psychiatry research, 351, 116617. https://doi.org/10.1016/j.psychres.2025.116617
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