Cannabis Use in Youth Tied to Altered Cognitive Trajectories
Key Clinical Summary
- In a longitudinal analysis of 11,036 participants from the Adolescent Brain Cognitive Development study, youth who initiated cannabis use showed altered neurocognitive trajectories from ages 9 to 17 across memory, processing speed, inhibitory control, language, visuospatial processing, and working memory.
- Secondary hair analyses in 645 participants found that THC-positive hair tests were associated with worse age-related episodic memory trajectories, whereas CBD-positive youth did not differ significantly from controls.
- The investigators combined self-report with urine, oral fluid, breath, and hair toxicology to improve exposure classification and adjusted for multiple confounders, including sociodemographic factors, family history, prenatal exposure, psychopathology, and other substance use.
A large US longitudinal study published in Neuropsychopharmacology found that adolescents who initiated cannabis use showed flatter neurocognitive development over time than peers who did not use cannabis.
The analysis drew on the Adolescent Brain Cognitive Development study and paired self-reported substance use with toxicology testing to better identify cannabis exposure.
Study Findings
The study evaluated 11,036 participants aged 9 to 17 years in the primary analysis, with 47% female and 53% male participants. Investigators used longitudinal mixed models to examine how cannabis onset related to neurocognitive performance over time while accounting for participant, site, family clustering, and a broad set of confounders.
Cannabis onset was identified most often by self-report, accounting for 67% of cases, followed by hair testing at 22%, urine toxicology at 21%, oral fluid testing at 5%, and medicinal cannabidiol (CBD) reporting at 3%; categories were not mutually exclusive.
Across the primary models, cannabis use interacted with age for several domains:
- working memory (β = −0.52, b = −1.32, 95% CI:-1.80,−0.84, p < 0.0001, FDR-p < 0.0001);
- episodic memory β = -0.32, b = −1.20, 95% CI:-1.54,-0.86, p < 0.0001, FDR-p < 0.0001);
- processing speed (β = -0.24, b = -1.13, 95% CI:-1.53,-0.74, p < 0.0001, FDR-p < 0.0001);
- inhibitory control (β = −0.21, b = −0.52, 95 %CI:−0.73,−0.31, p < 0.0001, FDR-p < 0.0001);
- immediate recall (β = -0.21, b = -0.08, 95% CI:−0.15,−0.01, p = 0.02, FDR-p = 0.03);
- long-delay memory (β = -0.21, b = -0.14, 95% CI:−0.25,−0.04, p = 0.008, FDR-p = 0.01);
- visuospatial performance (β = -0.16, b = -0.39, 95% CI: -0.63,-0.16, p = 0.001, FDR-p = 0.003);
- receptive language (β = -0.14, b = -0.36, 95% CI:−0.51,−0.21, p < 0.0001, FDR-p < 0.0001); and
- oral reading (β = -0.11, b = -0.25, 95% CI:−0.37,−0.12, p = 0.0001, FDR-p = 0.0003).
In several domains, youth later identified as cannabis users performed better in late childhood but showed less improvement over adolescence, with controls overtaking them by mid- to late adolescence.
In the secondary analysis of 645 participants with repeat hair testing at ages 12 to 16 years, THC-positive hair status predicted worse episodic memory trajectories versus controls (β = -0.60, b = -2.37, 95% CI:-4.08,-0.66, p = 0.007). The CBD-positive group did not differ significantly from controls, although the authors cautioned that the CBD-positive subgroup was small, with 21 participants.
Clinical Implications
For clinicians, the report adds longitudinal evidence that adolescent cannabis exposure may be associated with slower gains in several cognitive domains during a critical developmental window. The pattern described in the paper is not a simple cross-sectional deficit. Instead, it is one of reduced age-related improvement over time, which may be more relevant to counseling adolescents and families about functional outcomes.
The paper also highlights the limits of relying on self-report alone in adolescent substance-use research. By combining interviews with toxicology, the investigators aimed to reduce exposure misclassification, an issue they note has affected prior studies. That approach is clinically relevant because real-world histories may undercapture cannabis exposure, especially in younger patients.
The THC-specific hair findings are also notable, although they should be interpreted cautiously. They suggest that recent THC exposure, rather than CBD exposure, may be more closely tied to worse episodic memory trajectories in adolescence, but the authors state that continued follow-up into young adulthood is needed.
Expert Commentary
“[Our] findings support interventions aimed at delaying cannabis initiation during early adolescence and integrating neuroscience-informed psychoeducation about cognitive development during sensitive periods,” concluded Natasha E. Wade, PhD, Department of Psychiatry, University of California San Diego, and study co-authors. “Continued monitoring of this cohort will clarify cannabinoid-cognition relationships into young adulthood, including the impact of timing of cannabis use initiation.”
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