Background Tobacco use is the leading cause of preventable disease and death globally. The 2014 Surgeon General's Report included new diseases linked to smoking, including liver and colon cancer, diabetes and tuberculosis. As more diseases are linked to smoking, which diseases should we communicate to the public and what message source has the most impact? Methods Data were collected through a nationally representative phone survey of US adults (N = 5014), conducted from September 2014 through May 2015. We experimentally randomized participants to a 2 (new smoking disease messages - liver and colon cancers compared to diabetes and tuberculosis) by 4 (message sources - CDC, FDA, Surgeon General, and none) experiment. The outcome was message believability. Results About half the sample was female (51.5%) and 17.8% were a current smoker. Overall, 56% of participants said the messages were very believable. Cancer messages (liver and colon cancer) were significantly more believable than messages about chronic disease (tuberculosis and diabetes), 61% vs. 52%. Smokers were less likely to report both sets of new disease messages as very believable compared to non-smokers. Significantly more smokers intending to quit (44.5%) found the messages to be very believable compared to smokers not intending to quit (22.6%). Believability did not differ by message source. Conclusion Important differences exist in believability of disease messages about new tobacco-related information. Messages emphasizing the causal link between smoking and new diseases should be considered for use in mass media campaigns
