Purpose Lab experiments on cigarette warnings typically use a brief one-time exposure that is not paired with the cigarette packs smokers use every day, leaving open the question of how repeated warning exposure over several weeks may affect smokers. This proof of principle study sought to develop a new protocol for testing cigarette warnings that better reflects real-world exposure by presenting them on cigarette smokers’ own packs.

Methods We tested a cigarette pack labelling protocol with 76 US smokers ages 18 and older. We applied graphic warnings to the front and back of smokers’ cigarette packs.

Results Most smokers reported that at least 75% of the packs of cigarettes they smoked during the study had our warnings. Nearly all said they would participate in the study again. Using cigarette packs with the study warnings increased quit intentions (p<0.05).

Conclusions Our findings suggest a feasible pack labelling protocol with six steps: (1) schedule appointments at brief intervals; (2) determine typical cigarette consumption; (3) ask smokers to bring a supply of cigarette packs to study appointments; (4) apply labels to smokers’ cigarette packs; (5) provide participation incentives at the end of appointments; and (6) refer smokers to cessation services at end of the study. When used in randomised controlled trials in settings with real-world message exposure over time, this protocol may help identify the true impact of warnings and thus better inform tobacco product labelling policy.

Clinical trial number NCT02247908.