Importance: Pictorial warnings on cigarette packs draw attention and increase quit intentions, but their effect on smoking behavior remains uncertain.
Objective: To assess the effect of adding pictorial warnings to the front and back of cigarette packs.
Design, setting, and participants: This 4-week between-participant randomized clinical trial was carried out in California and North Carolina. We recruited a convenience sample of adult cigarette smokers from the general population beginning September 2014 through August 2015. Of 2149 smokers who enrolled, 88% completed the trial. No participants withdrew owing to adverse events.
Interventions: We randomly assigned participants to receive on their cigarette packs for 4 weeks either text-only warnings (one of the Surgeon General's warnings currently in use in the United States on the side of the cigarette packs) or pictorial warnings (one of the Family Smoking Prevention and Tobacco Control Act's required text warnings and pictures that showed harms of smoking on the top half of the front and back of the cigarette packs).
Main outcomes and measures: The primary trial outcome was attempting to quit smoking during the study. We hypothesized that smokers randomized to receive pictorial warnings would be more likely to report a quit attempt during the study than smokers randomized to receive a text-only Surgeon General's warning.
Results: Of the 2149 participants who began the trial (1039 men, 1060 women, and 34 transgender people; mean [SD] age, 39.7 [13.4] years for text-only warning, 39.8 [13.7] for pictorial warnings), 1901 completed it. In intent-to-treat analyses (n = 2149), smokers whose packs had pictorial warnings were more likely than those whose packs had text-only warnings to attempt to quit smoking during the 4-week trial (40% vs 34%; odds ratio [OR], 1.29; 95% CI, 1.09-1.54). The findings did not differ across any demographic groups. Having quit smoking for at least the 7 days prior to the end of the trial was more common among smokers who received pictorial than those who received text-only warnings (5.7% vs 3.8%; OR, 1.53; 95% CI, 1.02-2.29). Pictorial warnings also increased forgoing a cigarette, intentions to quit smoking, negative emotional reactions, thinking about the harms of smoking, and conversations about quitting.
Conclusions and relevance: Pictorial warnings effectively increased intentions to quit, forgoing cigarettes, quit attempts, and successfully quitting smoking over 4 weeks. Our trial findings suggest that implementing pictorial warnings on cigarette packs in the United States would discourage smoking.
Trial registration: clinicaltrials.gov Identifier: NCT02247908.