Genetic Variations in the Cannabinoid System Affected How the Brain Responds to Marijuana Cues | Research

The takeaway

Specific genetic variants in the CNR1 (cannabinoid receptor) and FAAH (endocannabinoid-degrading enzyme) genes were associated with greater brain reward-area activation when cannabis users viewed marijuana cues.

Read this if you are interested in how your genetics might affect your brain response to cannabis cues.

Risk alleles in two cannabinoid system genes additively increased brain reward responses to marijuana cues

What the researchers found

Thirty-seven regular marijuana users who had been abstinent for 3 days underwent fMRI while exposed to marijuana cues. They were grouped by genotype on two gene variants previously linked to cannabis dependence.

Carriers of the CNR1 rs2023239 G allele showed significantly greater activation in reward-related brain areas (orbitofrontal cortex, inferior frontal gyrus, anterior cingulate) when viewing marijuana cues.

FAAH rs324420 C/C homozygotes showed greater activation in the orbitofrontal cortex, anterior cingulate, and nucleus accumbens compared to A-allele carriers.

The total number of risk alleles across both genes was positively correlated with neural response in the orbitofrontal cortex and nucleus accumbens, showing an additive genetic effect on brain reward activation.

Why it matters

This study identified a biological mechanism through which genetic variations in the cannabinoid system could increase vulnerability to cannabis dependence: enhanced brain reward responses to drug cues.

The numbers in context

37 participants, 3 days abstinent. Two SNPs tested: CNR1 rs2023239 and FAAH rs324420. Both independently associated with greater reward-area activation. Additive effect of risk alleles on OFC and NAc response.

How the study worked

Cross-sectional neurogenetics study. Thirty-seven 3-day-abstinent regular marijuana users were genotyped for CNR1 rs2023239 and FAAH rs324420 SNPs. fMRI was collected during a cue-elicited craving paradigm. Between-group comparisons and correlation analyses examined genetic effects on brain activation.

What this study cannot tell us

Small sample for a genetics study (37 participants). Cross-sectional design. Only two SNPs examined from a complex polygenic trait. No non-using control group. Three days of abstinence may not eliminate all acute withdrawal effects.

How to read the evidence

Small neurogenetics study (n=37) examining only two gene variants. Interesting mechanistic findings but limited power and replication needed.

When this study was published

Published in 2010. Cannabis genetics research has expanded with genome-wide association studies, though the specific variants identified here have received further study.

The bigger picture

Understanding genetic contributions to cannabis cue reactivity could eventually help identify individuals at higher risk for developing cannabis dependence and could inform personalized prevention or treatment approaches.

Questions still open

Could genetic screening identify at-risk individuals before cannabis use begins? Do these genetic effects interact with other substance use? Would targeted interventions for high-risk genotypes improve treatment outcomes?

Common questions

Do your genes determine whether you will become addicted to cannabis?

Genes influence risk but do not determine outcomes. This study found that certain genetic variants were associated with stronger brain responses to cannabis cues, which could increase vulnerability. However, addiction involves many environmental and personal factors beyond genetics.

What are CNR1 and FAAH?

CNR1 is the gene for the CB1 cannabinoid receptor (what THC binds to). FAAH is the gene for the enzyme that breaks down anandamide (an endocannabinoid). Variations in these genes can affect how strongly the cannabinoid system responds to both natural and external cannabinoids.

Read the original research

Individual and additive effects of the CNR1 and FAAH genes on brain response to marijuana cues.

Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 35(4), 967-75

View on PubMed ↗Publisher’s paper ↗

Citation

Filbey, Francesca M; Schacht, Joseph P; Myers, Ursula S; Chavez, Robert S; Hutchison, Kent E. (2010). Individual and additive effects of the CNR1 and FAAH genes on brain response to marijuana cues.. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 35(4), 967-75. https://doi.org/10.1038/npp.2009.200