Adolescent marijuana users showed poorer verbal learning, working memory, and attention accuracy compared to controls, with memory improving after 2-3 weeks of abstinence but attention deficits persisting throughout.
Read this if you are a teen who uses cannabis and wants to know what happens to your brain when you stop.
Memory recovered by weeks 2-3; attention deficits persisted through 3 weeks of abstinence
What the researchers found
Nineteen adolescent marijuana users (ages 15-19) and 21 non-using controls were tested at three time points: after 3 days, 2 weeks, and 3 weeks of confirmed abstinence.
Marijuana users performed significantly worse on verbal learning (p<0.01), verbal working memory (p<0.05), and attention accuracy (p<0.01) compared to controls.
Verbal learning improved after 2 weeks of abstinence, and working memory improved after 3 weeks, suggesting these deficits can recover.
However, attention accuracy remained impaired throughout the entire 3-week abstinence period, suggesting more persistent effects on prefrontal cortex function.
Abstinence was verified through decreasing THC metabolite levels on serial urine drug screens.
Why it matters
This study provided the first longitudinal evidence of cognitive recovery patterns in adolescent marijuana users, showing that some deficits resolve relatively quickly while others persist, information critical for teens considering quitting.
The numbers in context
19 users, 21 controls, ages 15-19. Verbal learning improved by week 2. Working memory improved by week 3. Attention accuracy remained impaired through week 3.
How the study worked
Longitudinal study of 19 adolescent marijuana users and 21 controls. Participants completed neuropsychological testing at 3 days, 2 weeks, and 3 weeks of abstinence. Abstinence verified by serial urine drug screens showing decreasing THC metabolite levels.
What this study cannot tell us
Small sample (19 users). Three weeks may not be enough time for full recovery. Practice effects from repeated testing could mask or enhance recovery patterns. Participants had limited alcohol and other drug use but these could still confound results.
How to read the evidence
Small longitudinal study (n=40) with verified abstinence, providing useful recovery trajectory data but limited power and duration.
When this study was published
Published in 2010. Subsequent research has continued to examine cognitive recovery patterns in adolescent cannabis users, generally supporting differential recovery rates.
The bigger picture
The differential recovery pattern (memory recovers, attention persists) suggests that cannabis affects different brain systems in different ways during adolescent development. The persistence of attention deficits raises questions about whether they would eventually resolve with longer abstinence.
Questions still open
- Would attention deficits resolve with longer abstinence? Are the persistent attention effects specific to adolescent-onset use? Could the recovery pattern help motivate teens to quit?
Common questions
How long does it take for memory to recover after quitting cannabis?
Why did attention not recover?
Read the original research
Longitudinal study of cognition among adolescent marijuana users over three weeks of abstinence.
Addictive behaviors, 35(11), 970-6
Citation
Hanson, Karen L; Winward, Jennifer L; Schweinsburg, Alecia D; Medina, Krista Lisdahl; Brown, Sandra A; Tapert, Susan F. (2010). Longitudinal study of cognition among adolescent marijuana users over three weeks of abstinence.. Addictive behaviors, 35(11), 970-6. https://doi.org/10.1016/j.addbeh.2010.06.012
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