In the wGRS analyses highly similar results were obtained for the 3-SNP and 4-SNP wGRSs; only results for the 4-SNP wGRS are presented. For ease of interpretation, the wGRS was constructed as a weighted sum of major alleles (all of which increase nicotine clearance rate). In the wGRS meta-analysis of 3954 current smokers statistically significant association was detected for quantitative CPD (beta = 0.10, 95% CI 0.04–0.16, p = 0.0019), suggesting that individuals with faster metabolism smoke more. The wGRS meta-analysis for current (N = 3954) vs. former (N = 3543) smoking showed association with increased likelihood of being a former smoker (OR = 1.39, 95% CI 1.09–1.76, p = 0.007). Similarly, the major allele of CYP2A6*2 showed a trend of association with increased likelihood of being a former smoker (OR = 1.03, 95% CI 0.72–1.47, p = 0.89), although the results were not statistically significant. To scrutinize potential confounders for cessation, we utilized available questionnaire data and excluded NAG-FIN individuals who either have a DSM-IV major depression disorder diagnosis or report quitting due to adverse health consequences and FINRISK
