To identify the candidate genetic association studies, we performed a search for all abstracts deposited in PubMed database (National Center for Biotechnology Information; NCBI) using the keywords '("addiction" OR "abuse*") AND ("genetic*" AND "association*")'. To identify publications using different phenotype terms other than 'addiction' or 'abuse', we also identify candidate genetic association studies from published reviews selected from PubMed query under the keywords '("addiction" OR "abuse*" OR "dependen*") AND "genetic*" AND Review[ptyp]'. The combined approach resulted in 886 articles. All 886 abstracts were retrieved from PubMed database and manually curated by two independent reviewers. Only those studies that met the following criteria were included in further analyses: (i) It must represent an assessment of association between a polymorphic genetic marker (including SNP and microsatellite markers) and drug addiction phenotypes. Only studies focused exclusively on case-control or population-based designs were included. Studies on markers with more than three alleles (which are generally more difficult to determine unequivocally across different laboratories) or those with an otherwise complex allelic architecture were not considered for meta-analysis. (ii) The study must be published in a
