Identifying principles for effective messages about chemicals in cigarette smoke.

US law requires the Food and Drug Administration (FDA) to disclose information on harmful and potentially harmful chemicals in cigarette smoke (i.e., constituents) to the public. To inform this effort, we sought to identify principles for creating constituent messages that effectively discourage smoking. Participants were an online convenience sample of 1148 US smokers ages 18+. We developed a library of 76 messages about constituents only and constituents plus contextualizing information (i.e., toxic products that also contain the chemical, health effects, or both). We randomized smokers to receive 1 message from each of 7 message panels in a mixed between-/within-subjects experiment. Participants rated each message on perceived message effectiveness. Results indicated that smokers perceived messages about arsenic, formaldehyde, lead, uranium, and ammonia as more effective than messages about nitrosamines. Messages that contained information on toxic products, health effects, or both received higher effectiveness ratings than constituent-only messages. Among constituent-only messages, those that referenced multiple constituents received higher effectiveness ratings than those with fewer constituents. We conclude that chemical messages may have more impact if they pair known constituents with toxic product or health effect information. These message principles can be used to inform studies examining the impact of constituent messages on smoking beliefs and behavior.