Next, we combined the genetic risks defined by CYP2A6 and CHRNA5 genotypes into a variable representing the combined genetic risk with four levels. There was a nonlinear effect for NRT as a function of the four-level combined genetic risk (interaction effect size=0.75, 95%CI=0.58-0.96, p=0.021), but not for bupropion (interaction effect size=1.03, 95%CI=0.82-1.31, p=0.79, Table S5).
