Mice exposed to both THC and stress during adolescence showed impaired fear extinction in adulthood, along with reduced activity in the amygdala and prefrontal cortex, but neither factor alone produced this effect.
Researchers studying adolescent vulnerability, parents of teens who use cannabis, and anxiety disorder specialists.
Only THC + stress combined impaired adult fear extinction
What the researchers found
Adolescent mice given both THC and stress showed impaired cued fear extinction in adulthood, with decreased neuronal activity in the basolateral amygdala and infralimbic prefrontal cortex. These mice also had more immature dendritic spines in BLA pyramidal neurons and elevated corticosterone after fear conditioning. Crucially, neither THC nor stress alone produced these effects.
Why it matters
Many adolescents who use cannabis are also experiencing significant stress. This study shows these two factors interact to produce long-lasting anxiety-related brain changes that neither factor would cause alone.
The numbers in context
THC + stress group showed impaired fear extinction. Decreased c-Fos in BLA and infralimbic cortex. Increased immature dendritic spines in BLA. Elevated corticosterone after fear conditioning. Neither THC nor stress alone produced these effects.
How the study worked
Adolescent mice received THC treatment and/or stress exposure. In adulthood, they underwent cued fear conditioning and extinction testing. Brain tissue was analyzed for neuronal activity (c-Fos), structural plasticity (dendritic spines), and corticosterone levels.
What this study cannot tell us
Mouse model; human translation uncertain. Only one THC dose regimen and one type of stress were tested. Fear extinction is a model for anxiety but does not fully replicate human anxiety disorders.
How to read the evidence
Preliminary: animal study with a specific interaction design, important but not directly translatable.
When this study was published
Published in 2019.
The bigger picture
This helps explain why some adolescent cannabis users develop anxiety disorders while others do not. The combination of cannabis and environmental stress may be the key risk factor, not cannabis exposure alone.
Questions still open
- What types of real-world stressors interact most strongly with cannabis? Would CBD mitigate the combined THC + stress effects? Are there critical windows during adolescence when this interaction is most harmful?
Common questions
What is fear extinction?
Why does the combination matter more than either alone?
Read the original research
Concomitant THC and stress adolescent exposure induces impaired fear extinction and related neurobiological changes in adulthood.
Neuropharmacology, 144, 345-357
Citation
Saravia, Rocio; Ten-Blanco, Marc; Julià-Hernández, Marina; Gagliano, Humberto; Andero, Raül; Armario, Antonio; Maldonado, Rafael; Berrendero, Fernando. (2019). Concomitant THC and stress adolescent exposure induces impaired fear extinction and related neurobiological changes in adulthood.. Neuropharmacology, 144, 345-357. https://doi.org/10.1016/j.neuropharm.2018.11.016
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