Among 115 young adults, those with cannabis use disorder had significantly lower IQ (driven by verbal IQ) compared to controls, but showed no differences in executive function, working memory, attention, or episodic memory.
Neuropsychology researchers; clinicians assessing cognitive impacts of cannabis use.
d = 0.862 effect size for IQ deficit (driven by verbal IQ)
What the researchers found
CUD participants had significantly lower IQ with a strong effect size (p < .001, d = 0.862), driven specifically by lower verbal IQ. This finding survived adjustment for education years. No other cognitive domains showed significant differences, and neither problematic use severity nor dosage was associated with cognition.
Why it matters
The selective verbal IQ deficit is striking because it survived correction for education and was not accompanied by impairments in other domains. This specificity suggests cannabis use disorder may affect certain aspects of language-mediated intelligence while leaving other cognitive functions intact in young adults.
The numbers in context
IQ difference: p < .001, d = 0.862 (strong effect). Driven by verbal IQ. Survived education adjustment. No significant effects on executive function, working memory, episodic memory, attention, or verbal reasoning. 83 CUD vs 32 controls.
How the study worked
Cross-sectional study of 115 young adults (83 with CUD, 32 controls, ages 18.5-32.5). Comprehensive cognitive battery assessed executive function, working memory, episodic memory, verbal reasoning, attention, and IQ. All analyses accounted for alcohol/nicotine use and trait anxiety.
What this study cannot tell us
Cross-sectional design cannot determine whether lower verbal IQ preceded or resulted from CUD. Pre-existing verbal IQ differences could predispose individuals to CUD rather than cannabis causing IQ decline. The non-treatment-seeking sample may not represent more severe CUD.
How to read the evidence
Moderate: strong effect size with comprehensive cognitive battery and confound control, but cross-sectional design and non-treatment-seeking sample limit interpretation.
When this study was published
2025 study.
The bigger picture
Combined with the companion study showing preserved social cognition, a pattern emerges: CUD in young adults may selectively affect verbal intellectual capacity while sparing social understanding, executive function, and memory. This targeted profile differs from the broad cognitive decline often assumed.
Questions still open
- Does the verbal IQ deficit represent a consequence of cannabis use or a pre-existing trait? Would verbal IQ recover with sustained cannabis abstinence? Is verbal IQ decline more pronounced in those who began using cannabis earlier?
Common questions
Does cannabis lower IQ?
Why only verbal IQ and not other cognitive functions?
Read the original research
Cognitive performance in young adults who endorse a cannabis use disorder.
Comprehensive psychiatry, 142, 152620
Citation
Abbott, Gabrielle; Greenwood, Lisa; Bartschi, Jessica G; Dunsford, Suraya; Goodwin, Isabella; Paloubis, Anastasia; Valera, Marianna Quinones; McTavish, Eugene; Verdejo-Garcia, Antonio; Cousijn, Janna; Chan, Gary C K; Solowij, Nadia; Lorenzetti, Valentina. (2025). Cognitive performance in young adults who endorse a cannabis use disorder.. Comprehensive psychiatry, 142, 152620. https://doi.org/10.1016/j.comppsych.2025.152620
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