Using Novel Labeling to Improve Public Understanding of Nicotine in Electronic Nicotine Delivery Systems (ENDS): Nicotine Concentration and Nicotine Flux - Project Summary Use of Electronic Nicotine Delivery Systems (ENDS) can have positive and negative effects on public health. Ideally, people who smoke would switch to ENDS, and vulnerable populations like youth would avoid ENDS altogether. Yet, most adults who use ENDS also smoke, and ENDS have been the most popular nicotine product among youth since 2014. Effective informational labels for the nicotine strength of ENDS could help to address these problems. For smokers who want to switch to ENDS, easily selecting a product with sufficient nicotine to facilitate a complete switch is critical. For youth, informative labels may deter ENDS uptake, use of high-nicotine ENDS, and development of nicotine dependence. The FDA requires nicotine concentration labels on ENDS, typically in mg/mL or percent, but neither youth nor adults understand these metrics. We previously pilot tested new nicotine concentration labels that improved ENDS users' ability to interpret the strength and addictiveness of nicotine in ENDS. Here, we propose to extend our work to develop two labels: 1) a nicotine concentration label that could replace all current FDA-required ENDS nicotine concentration labels, and 2) a novel, potentially more informative label for nicotine emissions (“flux”) from popular closed-system devices like Vuse and JUUL. In Aim 1, we will refine our piloted nicotine concentration label by re-anchoring the nicotine strength categories on the label (e.g., medium, high) to the nicotine content in cigarettes. We also will develop nicotine flux labels for closed-system ENDS, which have fixed, calculatable nicotine emissions; are the most popular device type; and are the only device type to receive FDA approval for sales in the United States. Flux, the rate of nicotine emissions from ENDS, better approximates nicotine delivery than concentration alone. We will employ qualitative methods (i.e., expert feedback, focus groups) to identify the optimal scaling for our concentration label and to determine key features for inclusion on our flux labels. In Aim 2, we will compare the mg/mL market label (the top-performing market label from our prior work), optimized nicotine concentration label, and flux labels. We will survey 2,000 youth and adults who use ENDS, cigarettes, or no tobacco products to compare the ability of our new labels to accurately convey ENDS nicotine strength relative to current market labeling and to each other. We also will assess perceived addictiveness, perceived label utility, and product use intentions. We expect the new concentration and flux labels to more accurately convey ENDS nicotine strength than mg/mL alone. We also expect the new labels to better convey information about addictiveness, to be rated as having more utility than mg/mL, to decrease use intentions among never users, and to increase intentions to use ENDS in a quit smoking attempt. Project findings will provide the FDA a superior alternative to current nicotine concentration labels for all ENDS and will indicate if nicotine flux labeling has added benefit for the most popular ENDS device type: closed-system ENDS. In sum, the proposed project will increase public understanding of nicotine concentrations of all ENDS and nicotine emissions from closed-system ENDS.