Objectives: Actual use of nicotine pouch products is not well studied. The objectives of this study were to characterize on!(R) 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 similar to 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.