People with more CB1 receptors in their right amygdala experienced more anxiety after taking THC, connecting the brain's fear center to cannabis-related anxiety for the first time in humans.
Read this if you want to understand why some people get anxious from cannabis while others don't.
More CB1 receptors in the amygdala = more THC-induced anxiety
What the researchers found
In 14 healthy males studied with both fMRI and PET imaging, a 10mg oral dose of THC induced anxiety and changed how the right amygdala responded while processing fearful faces. Both of these effects, the subjective anxiety and the amygdala activation change, were positively correlated with the person's baseline CB1 receptor availability in the right amygdala.
In other words, men who had more CB1 receptors in their amygdala experienced more THC-induced anxiety. This provides the first direct evidence in humans linking individual variation in cannabinoid receptor density to vulnerability to cannabis-induced anxiety.
Why it matters
Cannabis-induced anxiety is one of the most common adverse effects of THC, but why some people experience it intensely while others do not has been unclear. This study identifies a biological marker, CB1 receptor density in the amygdala, that predicts individual vulnerability. This could eventually help predict who is likely to have negative anxiety responses to cannabis.
The numbers in context
14 healthy males. 10mg oral THC vs placebo. CB1 availability in right amygdala positively correlated with both THC-induced anxiety and right amygdala activation during fear processing.
How the study worked
Double-blind, placebo-controlled crossover design. 14 healthy males underwent fMRI on two occasions one month apart, after either 10mg oral THC or placebo, while performing a fear-processing task. CB1 receptor availability was independently measured using PET with the radioligand [11C]MePPEP.
What this study cannot tell us
Very small sample (14 men only). No women were included. A single THC dose was tested. The correlational design cannot determine causation. PET imaging measures receptor availability, which reflects both receptor density and occupancy. The findings may not generalize to smoked or vaped cannabis.
How to read the evidence
Small randomized controlled trial combining fMRI and PET imaging. Innovative multimodal design but very limited sample size.
When this study was published
Published in 2017. Individual differences in cannabinoid receptor distribution continue to be studied as predictors of cannabis responses.
The bigger picture
The amygdala is the brain's threat detection center, and it has abundant CB1 receptors. This study connects the dots: THC acts on these receptors to modify fear processing, and people with more receptors experience more of this effect. This individual variation in receptor density could help explain the wide range of anxiety responses to cannabis across the population.
Questions still open
- Would the same relationship between CB1 density and anxiety hold in women? Does chronic cannabis use change amygdalar CB1 receptor density over time? Could CB1 receptor density be used as a biomarker to predict who will develop cannabis-related anxiety disorders?
Common questions
Why does cannabis make some people anxious but not others?
Can you test for CB1 receptor density?
Read the original research
Acute induction of anxiety in humans by delta-9-tetrahydrocannabinol related to amygdalar cannabinoid-1 (CB1) receptors.
Scientific reports, 7(1), 15025
Citation
Bhattacharyya, Sagnik; Egerton, Alice; Kim, Euitae; Rosso, Lula; Riano Barros, Daniela; Hammers, Alexander; Brammer, Michael; Turkheimer, Federico E; Howes, Oliver D; McGuire, Philip. (2017). Acute induction of anxiety in humans by delta-9-tetrahydrocannabinol related to amygdalar cannabinoid-1 (CB1) receptors.. Scientific reports, 7(1), 15025. https://doi.org/10.1038/s41598-017-14203-4
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