INTRODUCTION Alcohol consumption that damages health remains highly prevalent in Sweden despite macrolevel intervention measures such as availability, restrictions and taxation. As understanding of behaviour change develops, there may be an opportunity to enhance individual level interventions by targeting personal dimensions of behaviour, such as underlying motives for drinking alcohol and readiness to change behaviour. This protocol describes a randomised controlled trial aimed at estimating the effectiveness of an intervention tailored to motives and readiness to change.

METHODS AND ANALYSIS A three-arm, parallel groups, randomised controlled trial will be used to estimate the effects of a motives and readiness to change tailored intervention. We will use a Bayesian sequential design to decide when to stop recruitment, with target criteria for benefit, harm and futility. Recruitment will be completed via web adverts and social media. Inclusion criteria are being aged 18 or older, having access to a mobile phone and being classified as a risky drinker. Participants allocated to the two intervention groups will receive either a personalised digital intervention or an intervention with enhanced tailoring for motives and readiness to change. The personalised intervention consists of weekly screening, personalised feedback and tools for planning behaviour. The enhanced tailored version will follow the same logic but will contain materials tailored for individuals' drinking motives and readiness to change. The control group will be redirected to two national websites with information about alcohol and health. Outcome measures are weekly alcohol consumption and monthly heavy drinking episodes, which will be contrasted with regression models and estimated using Bayesian inference.

ETHICS AND DISSEMINATION Ethical approval was obtained from the Swedish Ethical Review Authority on 16 April 2024, (Dnr 2024-01630-01). The results of the study will be disseminated in academic journals and research conferences.

TRIAL REGISTRATION NUMBER The trial was preregistered in the ISRCTN Registry on 12 June 2024 (ISRCTN87600318).