A meta-analysis of 20 fMRI studies found that adult cannabis users showed increased activation in temporal and frontal brain regions with decreased activation in visual and insular areas, while adolescent users showed a different pattern of changes.
Read this if you want to understand how cannabis affects brain function differently depending on age.
Different brain activation patterns in adult versus adolescent cannabis users across 20 fMRI studies
What the researchers found
Researchers conducted separate meta-analyses of fMRI studies comparing brain function in adult and adolescent cannabis users to non-users during various cognitive tasks.
In adult cannabis users (530 users vs 580 controls across 13 studies), brain activation was increased in the superior and posterior temporal regions and inferior frontal gyrus, while decreased in the visual cortex, insula, and middle temporal gyrus. These changes may reflect compensatory neuroadaptive processes where the brain recruits additional regions to maintain cognitive performance.
In adolescent cannabis users (219 users vs 224 controls across 7 studies), the pattern was different: increased activation was found in the inferior parietal gyrus and putamen compared to controls. The distinct patterns between age groups suggest that cannabis affects developing and mature brains through different mechanisms.
The meta-analytic approach was important because individual fMRI studies of cannabis have produced inconsistent results, making it difficult to draw conclusions from any single study.
Why it matters
By pooling data across many studies, this meta-analysis resolves inconsistencies in individual brain imaging studies of cannabis effects. The finding that adults and adolescents show different patterns of altered brain function supports the argument that the developing brain responds differently to cannabis, with potentially different long-term consequences.
The numbers in context
20 studies included: 13 adult, 7 adolescent. Adults: 530 cannabis users vs 580 controls. Adolescents: 219 cannabis users vs 224 controls. Adult changes: increased temporal/frontal activation, decreased visual/insular activation. Adolescent changes: increased parietal/putamen activation.
How the study worked
Systematic literature search identified 20 manuscripts (13 adult, 7 adolescent studies) meeting inclusion criteria. Separate meta-analyses used coordinate-based methods to synthesize fMRI activation data across studies employing various cognitive tasks. Adult analyses: 530 cannabis users vs 580 controls. Adolescent analyses: 219 cannabis users vs 224 controls.
What this study cannot tell us
The studies included used different cognitive tasks, which complicates interpretation of pooled results. The meta-analysis cannot determine whether brain changes preceded or followed cannabis use. Cross-sectional data cannot assess whether changes are reversible. The adolescent analysis had fewer studies and participants than the adult analysis.
How to read the evidence
This is a meta-analysis of neuroimaging studies, providing strong synthesized evidence from 20 individual studies.
When this study was published
Published in 2018. Neuroimaging meta-analyses of cannabis effects continue to be updated as more studies accumulate.
The bigger picture
This meta-analysis provides a clearer picture of what cannabis does to brain function than any individual study can offer. The age-dependent patterns add to growing evidence that adolescent cannabis exposure has distinct neurobiological consequences, supporting policies that aim to delay the onset of cannabis use.
Questions still open
- Do the compensatory brain activation patterns in adult users normalize after cessation? Why does the adolescent brain show different activation changes than the adult brain? Are the functional changes associated with measurable cognitive impairment?
Common questions
Does cannabis change how the brain works?
Is the effect different for teenagers?
Read the original research
Residual effects of cannabis use in adolescent and adult brains - A meta-analysis of fMRI studies.
Neuroscience and biobehavioral reviews, 88, 26-41
Citation
Blest-Hopley, Grace; Giampietro, Vincent; Bhattacharyya, Sagnik. (2018). Residual effects of cannabis use in adolescent and adult brains - A meta-analysis of fMRI studies.. Neuroscience and biobehavioral reviews, 88, 26-41. https://doi.org/10.1016/j.neubiorev.2018.03.008
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