Observational studies show high rates of switching away from cigarettes among adult purchasers of JUUL-brand electronic nicotine delivery system (ENDS); data are needed to evaluate switching with JUUL in randomized general population trials. The association of ENDS flavor availability and switching is pertinent. This study assessed switch rates and smoking reduction among participants randomized to use JUUL in a choice of flavors or tobacco-only, compared to a condition provided smoking-cessation materials. U.S. adults who smoke cigarettes (N = 837; Mage [SD] = 45.99 years [11.48]; 18.76 cigarettes/day [SD = 7.86]; 50.2% female) from an address-based representative panel were randomized to receive JUUL for 6 months (5.0% nicotine; only Virginia Tobacco [N = 285] or choice of flavors [N = 281]), or smoking-cessation materials (quit advice [QA]; N = 271). Self-reported past 30-day smoking and cigarette consumption were assessed at 1, 3, and 6 months. Repeated-measure regressions assessed differences in smoking outcomes between groups. Only 2% of participants were planning to quit smoking within 30 days. Across the 6-month intervention, participants randomized to JUUL (vs. QA) had 6.57-fold greater odds of reporting past 30-day switching (95% CI [3.72-11.63]). Participants in the JUUL (vs. QA) group smoked 27% fewer cigarettes/day versus baseline (Rate Ratio [95% CI] = 0.73 [0.68-0.77]). Over half (51.8%) of the Virginia Tobacco group used other flavors (36.7% nontobacco flavors), contaminating randomized flavor-conditions. JUUL flavor groups did not differ in smoking outcomes (p > .48). Use of JUUL products may support complete switching away from cigarettes, including among those not ready to quit smoking. Results suggest a preference for nontobacco-flavored ENDS among adults who smoke, although smoking outcomes did not differ by flavor. (PsycInfo Database Record (c) 2024 APA, all rights reserved).