Heavy cannabis-using adolescents had smaller hippocampi even after nearly 7 months of abstinence
Fourteen heavy cannabis-using adolescents had significantly smaller hippocampal volumes than controls even after an average of 6.7 months of abstinence, with smaller right hippocampus correlated with heavier prior use.
Quick Facts
What This Study Found
Researchers compared hippocampal brain structure between 14 heavy cannabis-using adolescents (averaging 5.8 joints per day) and 14 matched controls using high-resolution MRI, after an average of 6.7 months of supervised abstinence.
Heavy cannabis users had significantly smaller right (p < 0.04) and left (p < 0.02) hippocampal volumes compared to controls. No significant differences were found in the amygdala.
In controls, larger hippocampal volumes correlated significantly with better verbal learning and memory scores. This normal brain-cognition relationship was absent in cannabis users.
Smaller right hippocampus volume was correlated with greater prior cannabis use (r = -0.57, p < 0.03), suggesting a dose-response relationship.
Key Numbers
14 cannabis users (5.8 joints/day average) vs 14 controls. Mean 6.7 months abstinence. Smaller left (p < 0.02) and right (p < 0.04) hippocampi. Right hippocampal volume correlated with use amount (r = -0.57, p < 0.03).
How They Did This
Cross-sectional MRI study comparing 14 treatment-seeking adolescents (aged 18-20) with heavy cannabis history to 14 demographically matched controls. High-resolution 3D MRI and California Verbal Learning Test administered after average 6.7 months of supervised drug abstinence.
Why This Research Matters
The persistence of hippocampal volume differences after nearly 7 months of abstinence suggested that heavy adolescent cannabis use may produce lasting structural brain changes, particularly in a region critical for memory and learning.
The Bigger Picture
These findings added to concerns about the vulnerability of the adolescent hippocampus to cannabis effects and raised questions about whether heavy early use could have lasting consequences for memory and learning ability.
What This Study Doesn't Tell Us
Small sample size (14 per group). Cross-sectional design cannot determine whether smaller hippocampi preceded or resulted from cannabis use. Treatment-seeking adolescents may not represent all cannabis users. No pre-use baseline imaging.
Questions This Raises
- ?Would hippocampal volumes recover with longer abstinence periods?
- ?Did the smaller hippocampi represent a risk factor for cannabis dependence rather than a consequence of use?
Trust & Context
- Key Stat:
- Smaller hippocampi persisted after 6.7 months of abstinence
- Evidence Grade:
- Small cross-sectional MRI study with well-matched controls and dose-response correlation, but cannot establish causation.
- Study Age:
- Published in 2011. Neuroimaging studies of adolescent cannabis users have expanded considerably since.
- Original Title:
- Medial temporal structures and memory functions in adolescents with heavy cannabis use.
- Published In:
- Journal of psychiatric research, 45(8), 1055-66 (2011)
- Authors:
- Ashtari, Manzar, Avants, Brian, Cyckowski, Laura, Cervellione, Kelly L, Roofeh, David, Cook, Philip, Gee, James, Sevy, Serge, Kumra, Sanjiv
- Database ID:
- RTHC-00469
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
Does heavy cannabis use shrink the hippocampus?
In this small study, heavy adolescent users (5.8 joints/day) had smaller hippocampal volumes that persisted after nearly 7 months of abstinence. However, the study could not determine whether cannabis caused the shrinkage or whether pre-existing smaller hippocampi increased vulnerability.
Does the brain recover after stopping cannabis?
After 6.7 months of abstinence, hippocampal volume differences were still present. Whether longer abstinence would show recovery was not tested. The normal relationship between hippocampal size and memory scores was also absent in the cannabis group.
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Cite This Study
https://rethinkthc.com/research/RTHC-00469APA
Ashtari, Manzar; Avants, Brian; Cyckowski, Laura; Cervellione, Kelly L; Roofeh, David; Cook, Philip; Gee, James; Sevy, Serge; Kumra, Sanjiv. (2011). Medial temporal structures and memory functions in adolescents with heavy cannabis use.. Journal of psychiatric research, 45(8), 1055-66. https://doi.org/10.1016/j.jpsychires.2011.01.004
MLA
Ashtari, Manzar, et al. "Medial temporal structures and memory functions in adolescents with heavy cannabis use.." Journal of psychiatric research, 2011. https://doi.org/10.1016/j.jpsychires.2011.01.004
RethinkTHC
RethinkTHC Research Database. "Medial temporal structures and memory functions in adolescen..." RTHC-00469. Retrieved from https://rethinkthc.com/research/ashtari-2011-medial-temporal-structures-and
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.