A specific gene variant in the cannabinoid receptor gene was linked to more frequent cannabis use around age 18 | Research

The takeaway

Carriers of the C allele at rs806374 in the cannabinoid receptor gene CNR1 used cannabis more frequently at the start of college (around age 18), but this genetic effect did not grow or shrink over the following six years.

Read this if you're interested in how genetics might influence cannabis use during the transition to adulthood.

CNR1 gene variant rs806374 associated with higher cannabis use at age 18 but not with use trajectory

What the researchers found

Using latent growth curve modeling across 10 waves of data from ages 18 to 24, one variant in the cannabinoid receptor gene CNR1 (rs806374) was significantly associated with cannabis use frequency. C carriers used cannabis more frequently at study onset (around age 18) compared to non-carriers.

This genetic effect was specific to the level of use, not its trajectory. The rate at which cannabis use changed over time (growth) did not differ by genotype. Peer drug use was a strong predictor of individual cannabis use that grew in effect size over time, but it did not moderate the genetic association.

Why it matters

This study pinpoints a developmental window (around age 18) when a specific genetic variant influences cannabis use frequency. The fact that the genetic effect was limited to initial level, not trajectory, suggests that genetic vulnerability to cannabis may operate primarily during the transition out of high school, after which environmental factors like peer influence become more important.

The numbers in context

rs806374 C carriers showed significantly higher cannabis use frequency at baseline (age ~18). Effect was on level only, not growth. 8 SNPs tested, 1 significant after multiple comparison correction. Peer drug use effect grew over time but did not moderate the genetic association. Sample: 334 non-Hispanic White participants across 10 waves.

How the study worked

Latent growth curve modeling of 10 longitudinal waves spanning ages 18.4 to 23.8 years in 334 non-Hispanic White participants. Eight independent SNPs in or near the CNR1 gene were tested for association with both level and growth of cannabis use. Peer drug use was included as a time-varying predictor and potential moderator. Corrections for multiple comparisons were applied.

What this study cannot tell us

Small sample size (334 participants) limits statistical power. Restricted to non-Hispanic White individuals, so findings may not generalize to other populations. Only one of eight tested SNPs was significant, and the effect was modest. Self-reported cannabis use may be inaccurate.

How to read the evidence

Longitudinal cohort study with genetic analysis. Strong repeated-measures design but limited by small sample size and restriction to one ethnic group.

When this study was published

Published in 2017. Larger genome-wide studies have since expanded the search for cannabis-associated genetic variants.

The bigger picture

Genetics and environment do not simply add up; they operate in developmental windows. This finding that a cannabinoid receptor gene variant matters most around age 18 suggests that genetic vulnerability to cannabis may be particularly relevant during specific life transitions, which could help target prevention efforts.

Questions still open

What is the functional mechanism by which rs806374 affects cannabinoid receptor signaling? Why does the genetic effect concentrate at age 18 specifically? Would the finding replicate in larger, more diverse samples? Does this variant interact with other genes to affect cannabis use risk?

Common questions

Is there a "cannabis gene"?

No single gene determines cannabis use. This study found one variant in the cannabinoid receptor gene that influenced use frequency at a specific age. Cannabis use is influenced by hundreds of genetic variants, each with small effects, combined with environmental factors.

Does peer influence override genetics?

In this study, peer drug use was a strong predictor of cannabis use that grew in importance over time, while the genetic effect remained stable. However, peers did not modify the genetic effect, suggesting these are independent pathways rather than one overriding the other.

Read the original research

Developmentally Specific Associations Between CNR1 Genotype and Cannabis Use Across Emerging Adulthood.

Journal of studies on alcohol and drugs, 78(5), 686-695

View on PubMed ↗

Citation

Ashenhurst, James R; Harden, K Paige; Mallard, Travis T; Corbin, William R; Fromme, Kim. (2017). Developmentally Specific Associations Between CNR1 Genotype and Cannabis Use Across Emerging Adulthood.. Journal of studies on alcohol and drugs, 78(5), 686-695.