CPD and pack-years are two correlated measures of smoking. In the ~40,000 individuals from UK Biobank with CPD and pack-years calculated, correlation between CPD and pack-years was 0.640. Interestingly, while pack-years was inversely correlated with smoking cessation (−0.18) i.e., the more years a smoker has been smoking the less likely they were to cease, CPD was positively correlated with smoking cessation (0.13) i.e., heavier smokers were more likely to stop smoking. In contrast, the DBH SNV, rs3025343, (first identified via its association with increased smoking cessation [6]) was associated with increased pack-years (P = 1.29 × 10−14) and increased CPD (P = 2.93 × 10−9) in our study. The association at DBH also represents the first time that a SNV has a smaller P-value for pack-years (n = 131,892) compared to CPD (n = 128,746). These findings may help elucidate the genetic basis of these correlated addiction phenotypes.
