Transitions from Exclusive Cigarette Smoking to Dual or Exclusive ENDS Use: Changes in Nicotine Dependence and Use Patterns, PATH Study Waves 1-7 (2013-2023).

INTRODUCTION: Electronic nicotine delivery systems (ENDS) can aid cigarette cessation in trials; however, in real-world cohorts, dual use is more common than switching to exclusive ENDS, raising questions about harm-reduction potential. We examined changes in Tobacco Dependence Index (TDI), smoking behavior, and ENDS use among exclusive smokers who transitioned to dual or exclusive ENDS use. METHODS: Adults in the Population Assessment of Tobacco and Health Study (Waves 1-7) contributed adjacent wave-pair episodes (baseline and follow-up). Outcomes included change in TDI (defined as the maximum of the cigarette- or ENDS-TDI for dual users), follow-up cigarette- and ENDS-TDI, non-daily smoking, ≥50% cigarettes-per-day (CPD) reduction, daily ENDS use, and pickups/day and puffs/pickup. Weighted generalized estimating equations adjusted for baseline TDI, wave, and demographics. RESULTS: Relative to remaining smokers, adjusted change in overall TDI was -6.26 for dual users and -10.81 for exclusive ENDS switchers (both p < .0001). Reductions in cigarette-TDI were small and nonsignificant for dual users (-1.72) but substantially larger for exclusive ENDS switchers (-33.90). However, dual users were more likely than remaining smokers to become non-daily smokers (RR 3.85) and achieve a ≥50% CPD reduction (RR 2.65). At follow-up, exclusive ENDS switchers scored higher on ENDS-TDI (+18.49 points) but lower on cigarette-TDI (-33.97 points) than dual users, alongside higher daily ENDS use (RR 2.08) and pickups/day (IRR 1.47), with similar puffs/pickup. CONCLUSIONS: Exclusive ENDS switchers reported the largest dependence reductions, whereas dual users showed moderate overall reductions but little change in cigarette dependence, consistent with a behavioral pattern of supplementation.