Cannabis users had worse verbal memory but adolescents were not more vulnerable than adults | Research

The takeaway

The CannTeen study found that cannabis users had worse verbal episodic memory than non-users, but contrary to expectations, adolescent users (16-17) were not more cognitively impaired than adult users (26-29).

Developmental neuroscientists, cannabis policy researchers, parents, and clinicians counseling young cannabis users.

Worse verbal memory in users, but no heightened adolescent vulnerability

What the researchers found

Cannabis users had significantly worse verbal episodic memory than controls (p=0.007). However, no significant differences were found between users and controls on spatial working memory or response inhibition, supported by Bayesian analyses. Critically, no interaction between age group and user status was found for any cognitive measure.

Why it matters

The adolescent brain is considered more vulnerable to cannabis, but this well-matched study did not find evidence for heightened adolescent vulnerability, challenging a widely held assumption.

The numbers in context

274 total participants. Users: 4 days/week, 2.5 days since last use. Verbal memory: F(1,268)=7.423, p=0.007. No significant user-control differences on spatial working memory or response inhibition. No age-by-user interaction for any measure.

How the study worked

Cross-sectional study from the CannTeen project: 76 adolescent cannabis users (16-17), 63 adolescent controls, 71 adult users (26-29), and 64 adult controls. Users matched on cannabis frequency (4 days/week) and time since last use (2.5 days). Tested verbal memory, spatial working memory, and response inhibition.

What this study cannot tell us

Cross-sectional design. Cannot determine if cognitive differences preceded cannabis use. Relatively small groups. Matching on frequency and recency of use may mask other exposure differences. Young adult age range (26-29) may still reflect ongoing neurodevelopment.

How to read the evidence

Well-designed cross-sectional study with matched groups and Bayesian analysis supporting null findings, but cannot establish causation.

When this study was published

Published in 2022.

The bigger picture

If adolescents are not uniquely vulnerable to cannabis-related cognitive effects compared to adults, the policy rationale for age-differentiated cannabis regulations may need to be reconsidered, or at least qualified.

Questions still open

Would longer-term follow-up reveal adolescent-specific vulnerabilities? Are there cognitive domains not tested that show age-specific effects?

Common questions

Does cannabis affect memory?

Yes. Cannabis users had significantly worse verbal episodic memory (story recall) than non-users. However, spatial working memory and response inhibition were not affected.

Is cannabis worse for teen brains than adult brains?

This study did not find evidence for that. Adolescent cannabis users (16-17) were not more cognitively impaired than adult users (26-29) on any measure tested, despite both groups being matched on usage patterns.

Read the original research

The CannTeen study: verbal episodic memory, spatial working memory, and response inhibition in adolescent and adult cannabis users and age-matched controls.

Psychopharmacology, 239(5), 1629-1641

View on PubMed ↗Publisher’s paper ↗

Citation

Lawn, W; Fernandez-Vinson, N; Mokrysz, C; Hogg, G; Lees, R; Trinci, K; Petrilli, K; Borissova, A; Ofori, S; Waters, S; Michór, P; Wall, M B; Freeman, T P; Curran, H V. (2022). The CannTeen study: verbal episodic memory, spatial working memory, and response inhibition in adolescent and adult cannabis users and age-matched controls.. Psychopharmacology, 239(5), 1629-1641. https://doi.org/10.1007/s00213-022-06143-3