Our GWAS meta-analysis included 17 074 ever smokers from five European-ancestry samples (Table 1). We used the FTND to categorize participants' dependence as mild (N=9137 with FTND score 0–3 or low-level smoking), moderate (N=4881 with FTND score 4–6) or severe (N=3056 with FTND score 7–10). We tested genotyped and 1000 Genomes–imputed SNPs and indels for association with categorical nicotine dependence in each sample and then combined the GWAS results using inverse variance-weighted meta-analysis with genomic control correction52 applied to each sample. Meta-analysis results for the 9.9 million tested SNPs/indels had no indication of bias (λgc=0.97, Supplementary Figure 2).
