The purpose of this randomized controlled trial is to determine whether constituent disclosures on cigarette packs increase intentions to quit smoking. Previous studies have been informative, but they have evaluated candidate graphic warnings, not constituent disclosures. Furthermore, they typically expose participants to messages in controlled but artificial experimental settings for a short period of time, using much lower frequency and shorter duration of message exposure than found in the real world. This study addresses these issues by evaluating the impact of constituent disclosures by randomly assigning smokers to have their cigarette packs labeled with constituent disclosure messages or cigarette butt littering messages.