Findings
We randomly assigned 722 participants to intervention or control groups. Biochemically verified continuous abstinence at 6 months was 6.9% (25/360) in the intervention group and 3.0% (11/362) in the control group. Smokers who received the personalized intervention had lower scores on intrinsic rewards of smoking and response costs of quitting in the protection motivation theory analysis. These two variables were also determinants of sustained abstinence, thus explaining why the intervention group had a higher quitting rate.