Communicating genetic information may increase medication adherence, but may also negatively impact motivation to quit if the initial attempt fails. We investigated the impact of genetic feedback on medication adherence and motivation to quit. We tested (1) whether adherence to NRT is greater following genetic (OPRM1 genotype) compared to phenotypic (heaviness of smoking) feedback, and (2) whether smokers who relapsed showed lower motivation to make another attempt following genetic compared to phenotypic feedback.