Booster effects and mechanisms of web-based personalised normative feedback alcohol intervention for college...

To evaluate the effects of booster and no booster versions of web-based alcohol Personalised Normative Feedback (PNF) and whether descriptive norms mediated and/or participant motivation moderated the effectiveness of the intervention in real world conditions (i.e. no financial incentives).

Pragmatic randomised controlled trial with 1-, 3-, and 6-month assessments. Brazilian college students reporting alcohol use in the last 12 months (N=931) were recruited from May/2020 to December/2022 and allocated to 1) No booster/single PNF(S-PNF); 2) Booster/multiple PNF(M-PNF); or 3) Assessment-only control. We applied Helmert coding [1: Any intervention (S-PNF or M-PNF) vs. Control; and 2: S-PNF vs. M-PNF].

typical number of drinks/week and maximum number of drinks/week; secondary outcomes: drinking frequency and number of consequences. Three-months assessment was the primary interval. Descriptive norms were tested as mediator. Interest, importance, and readiness to change were examined as moderators.

Compared to control, any intervention did not influence primary outcomes at 3-months or 6-months, but did at 1-month, when reduced typical drinking (IRR:0.77, 95%CI:0.66;0.90) and maximum number of drinks (IRR:0.69, 95%CI:0.58;0.82). There was an intervention effect on the consequences at 3-months. No differences were observed between S-PNF and M-PNF. No mediation effects were found at 3-months. At 6-months, there was an indirect effect on typical drinking through norms at 3-months (b=-0.82, 95%CI:-2.03;-0.12) and effects on maximum drinks through norms at 1-month (b=-0.54, 95%CI:-1.65;-0.02). No support for moderation was found.

Intervention reduced alcohol drinking at 1 month only and was not effective thereafter. Mechanisms of effect remain unclear.