CNR1 encodes the human endocannabinoid receptor 1 (CB1) which is the putative binding site for Δ9-tetrahydrocannabinol. CB1 knock-out mice do not display effects associated with cannabinoids (e.g., antinociception) [70]. Numerous studies have examined the relationship between variants in CNR1 and cannabis addiction as well as other substance use disorders (for review see [71]). The most frequently studied of these polymorphisms is the (AAT)n repeat in the 3′ untranslated region of the gene, a variable number of tandem repeats with unknown functional consequence. A recent meta-analysis reported that individuals with greater than 15 repeats may be at increased risk for addiction to illicit drugs [72•]. Other variants (e.g., rs1049353, rs806380) have produced inconsistent results, further complicated by the examination in some studies of addiction to all illicit drugs (even though cannabis is likely to be the most commonly used and misused of these).
