Abstract
BACKGROUND AND AIMS: Digital smoking cessation interventions have been shown to be effective in helping individuals achieve prolonged smoking abstinence. Nonetheless, the mechanisms that drive such effects are unclear. The current study aimed to estimate a digital smoking cessation intervention's natural direct and indirect effects. METHODS: This secondary analysis of mediated effects uses data from a randomised controlled trial which included participants who smoked at least one cigarette a week, had access to a mobile phone, and were 18 years or older. The comparator was existing smoking cessation support available to all members of the Swedish public. Primary outcomes were prolonged smoking abstinence and point prevalence of smoking abstinence, measured at 3- and 6-months post-randomisation. A counterfactual framework was used to estimate three hypothesised mediators of the intervention's effects: importance, knowledge of how to change (know-how), and confidence. RESULTS: Between 18/09/20 and 16/06/22, 1012 participants were randomised. The intervention led to improved confidence and know-how, which both partially mediated the effects of the digital intervention on smoking abstinence at 3- and 6 months post-randomisation. CONCLUSIONS: A digital smoking cessation intervention was found to partially affect smoking abstinence by improving individuals' confidence in their ability to quit smoking and developing knowledge on how to quit. Face-value single-item mediator measures, lack of blinding, and attrition limit the study. Future studies should address these limitations and assess additional mechanisms mediating intervention effects. TRIAL REGISTRATION: ISRCTN13455271.