Objectives. Excessive alcohol consumption increases when students enter university. This study tests whether combining (i) messages that target key beliefs from the theory of planned behaviour (TPB) that underlie binge drinking, (ii) a self-affirmation manipulation to reduce defensive processing, and (iii) implementation intentions (if-then plans to avoid binge drinking) reduces alcohol consumption in the first six months at university. Design. A 2 (self-affirmation) × 2 (TPB messages) × 2 (implementation intention) between-participants randomised controlled trial with six-month follow-up. Methods. Before starting university, students (N = 2,951) completed measures of alcohol consumption and were randomly assigned to condition in a full factorial design. TPB cognitions about binge drinking were assessed immediately post-intervention (n = 2,682). Alcohol consumption was assessed after one week (n = 1,885), one month (n = 1,389) and six months (n = 892) at university. TPB cognitions were assessed again at one and six months. Results. Participants who received the TPB messages had significantly less favourable cognitions about binge drinking (except perceived control), consumed fewer units of alcohol, engaged in binge drinking less frequently and had less harmful patterns of alcohol consumption during their first six months at university. The other main effects were non-significant. Conclusions. The findings support the use of TPB-based interventions to reduce students’ alcohol consumption, but question the use of self-affirmation and implementation intentions before starting university when the messages may not represent a threat to self-identity and when students may have limited knowledge and experience of the pressures to drink alcohol at university.