The JUUL2^® is a temperature regulated, electronic nicotine delivery system (ENDS) designed to provide reduced-risk alternatives to adult smokers who would otherwise continue to smoke cigarettes. In April 2022, three e-liquid formulations, Autumn Tobacco, Ruby Menthol, and Summer Menthol were introduced in the United Kingdom. Prior to market release, harmful and potentially harmful constituent (HPHC) levels were measured in aerosol generated from the JUUL2^® ENDS device with these three formulations. In this study, HPHC levels in these aerosols were compared with reported HPHC levels measured in smoke from the 3R4F reference cigarette. ENDS generally emit reduced levels HPHCs compared to combustible cigarettes; the degree of constituent reduction can vary across ENDS product designs. An assessment of aerosol constituent levels was determined to end of pod life. Based on U.S Food and Drug Administration, Premarket Tobacco Application and European Tobacco Products Directive guidance, selected aerosol constituents included primary constituents, carbonyls, esters, volatile organic compounds, nicotine degradants, metals, organic acids, TSNAs, glycidol, and pH. Reference cigarette 3R4F HPHC values measured in smoke generated under non-intense, [ISO 3308] and intense [ISO 20778] puffing regimes were obtained from the literature. These were compared to matched compounds measured in the aerosols from the JUUL2^® devices. There were substantial reductions in the number of detectable HPHCs in JUUL2^® aerosols relative to 3R4F smoke. Overall, the HPHC levels, excluding Nicotine, Menthol, Propylene Glycol and Glycerin, measured in aerosols from the JUUL^® device/e-liquids generated under intense and non-intense puffing regimens were, on average, ≥96% lower than those reported in 3R4F reference cigarette smoke.