First, we performed an integration and meta-analysis of candidate gene association studies of drug addiction. We retrieved 886 publications on candidate gene association studies of drug addiction from PubMed by keywords query and review paper curation (See details in Methods). Two hundred and twelve of these reports met our inclusion criteria, from which we extracted data on 506 allelic contrast tests for 286 genetic variants (Additional file 1). Thirty-five genetic variants were examined in case-control genotype comparisons from three or more independent datasets. We carried out meta-analyses of these 35 genetic variants under simple genetic models using both the random-effects model and fixed-effects model [22,23]. From these data, 12 genetic variants in 11 genes showed effects that reached statistical significance (Table 1, Additional file 2). We noted that most of these variants show comparatively weak genetic effects, with fixed effects summary odds ratios (OR) ranging from 0.52 to 2.34 (Table 1), typical results for studies on other highly heritable phenotypes with "common variants, common disease" design [3-6]. We further assessed the variants using criteria established by the HuGENet Road Map
