Study procedures
Within 45 days of the screening visit, eligible participants attended the study center for an 11-day confinement study that was divided into five different 48-h Study Periods (Supplementary Figure The 48-h Study Periods per product included one and a half days of product familiarization, in which subjects were required to participate in a minimum of six ad libitum use sessions of their assigned non-UB study products. The parameters for ad libitum use during product familiarization and AL test sessions were as follows: up to 10 min for the UB cigarettes, approximately 10 min (± 10 s) for the assigned ENDS, and 30 min (± 10 s) for the nicotine gum. During product familiarization, subjects were allowed to use the products longer if desired. On the last half-day of each Study Period, following a minimum 12-h overnight nicotine abstinence period, subjects participated in a 4-h test session using their assigned product. Baseline blood sampling and urge-to-smoke assessments were made prior to product use during the test session. During and after product use, participants underwent assessments for subjective effects and physiological changes and blood sampling for nicotine uptake. Additional details of study procedures are published in Campbell et al.