Objectives: Actual use of nicotine pouch products is not well studied. The objectives of this study were to characterize on ® nicotine pouch (Test Products (TP)) use behavior, including association with cigarette and smokeless tobacco (ST) product use. Methods: Adults who smoke cigarettes (AS) and/or adults who use ST (ASTU) (N=1147) that were not planning to quit and had expressed interest in trying and using TP after a 5-day trial were offered ad libitum use of TPs (7 flavors at 5 nicotine levels) for 6 weeks. Results: Participants used a median of ~5-6 pouches/day of a variety of flavors and nicotine levels. In the final week of the study, 27% of AS and 71% of ASTU reported no use of cigarettes or ST respectively, while reporting continued use of TPs. Additionally, 39% of AS and 14% of ASTU reduced consumption of cigarettes or ST products respectively by 50%-99%, compared to reported use at screening. We found a statistically significant inverse relationship between TP flavor varieties and number of cigarettes/ST. Conclusions: These data suggest that TPs can be potential substitutes for cigarettes/ST products, and complete switching may offer harm reduction potential for AS and ASTU not interested in quitting.