Limitations include sample size and choice of population. The rarity of the minor (A) allele prevented the attainment of a sample large enough to assess the effects of homozygosity. Thus, A/A and A/C individuals were combined into one group. Future studies should examine whether either allele has an additive effect on liability for CD. Additionally, although participants’ daily marijuana use allowed us to induce significant increases in withdrawal and craving after only 24 h of abstinence, these phenotypes, as well as sensitivity to the acute effects of marijuana, need to be examined in less frequent users, who may demonstrate different phenotypic association.
