Given the primary importance of the mu-opioid receptors in cannabinoid-opioid interplay, the gene encoding the mu-opioid receptor 1 (OPRM1) on chromosome 6q24-q25, is an excellent candidate gene for cannabis use, abuse and dependence. Intriguingly, the gene lies 64.7 Mb (Megabases) downstream from the 3’ end of the CNR1 gene. OPRM1 is a fairly large gene (124kb), with 4 exons. It has been widely studied for its role in alcohol, nicotine and substance dependence [129-136]. The most actively investigated polymorphism in this gene is A118G (rs1799971) which leads to a change in the function of exon 1. Studies have failed to consistently find an association between A118G and liability to drug dependence. We are not aware of any published association studies of cannabis dependence and polymorphisms in OPRM1.
