The U.S. FDA is required by law to publicly display a list of harmful and potentially harmful constituents (HPHCs) "by brand and by quantity in each brand and subbrand" in a format that is "understandable and not misleading to a lay person." An online experiment examined youth and adult understanding of which HPHCs are present in cigarette smoke, understanding of health effects of smoking cigarettes, and endorsement of misleading information after viewing HPHC information displayed in one of six formats. We recruited youth (N = 1324) and adults (N = 2904) from an online panel and randomized them to one of six formats of presenting HPHC information. Participants responded to survey items before and after exposure to an HPHC format. Understanding of HPHCs in cigarette smoke and understanding of health effects of cigarette smoking significantly increased pre- to post-exposure for all formats. Respondents (20.6% to 73.5%) endorsed misleading beliefs after exposure to information about HPHCs. Endorsement of the one misleading belief that was measured pre- and post-exposure significantly increased for viewers of four formats. All formats increased understanding of HPHCs in cigarette smoke and the health effects of smoking cigarettes, but some participants endorsed each misleading belief after exposure to HPHC information.