Testing alcohol container warning labels among alcohol consumers in the field over a 4-week period: a protocol for a randomized field trial.

Objective: Online and lab-based experiments examining the impact of alcohol labels typically test a one-time exposure to labels and assess short-term, non-behavioural outcomes. These studies do not simulate a real-world label dose or assess actual alcohol use. This pilot aimed to develop a new protocol for testing alcohol labels that better reflects real-world exposure by presenting labels on consumers' own alcohol products over time and assessing effects on several outcomes, including alcohol use.

Method: Forty alcohol consumers in Canada completed an online baseline survey, were randomized to one of two label conditions (Control: recycle label; Intervention: cancer warning label), mailed labels according to their assigned condition, and asked to affix one label to all alcohol containers in their home over the 29 days in February 2024. Online surveys assessed label effects at three follow-up points, and SMS texts were used to promote protocol adherence.

Results: The protocol had high adherence and retention, with no differences between conditions. Survey response rates remained high at follow-ups, ranging between 80%-100%. All participants (100%) said they were satisfied with the study and 94% would recommend to a friend. Preliminary label effectiveness results were promising - between baseline and Day 29, the mean number of standard drinks (SD) consumed in the past 7 days decreased in the intervention condition by -4.2SD (45%), and in the control by -0.3SD (3%).

Conclusions: Findings suggest this proof-of-principle protocol affixing labels on consumers' own alcohol products offers the potential for greater experimental control and real-world label dose than online or lab-based experiments.