The purpose of this study was to investigate how U.S. adult daily smokers actually used the HeatSticks in near to real-world conditions. This study was a single group, prospective observational study, implying an assessment of subject-reported stick-by-stick consumption of HeatSticks and of conventional cigarettes (CC). Participants received HeatSticks free of charge and were able to consume HeatSticks, CC and other nicotine containing products ad libitum. The study consisted of a 1-week baseline period, a subsequent 6-week observational period, and a 1-week close-out period. To ensure a good representation in terms of age, sex, race and income, 1,336 US adult daily smokers were recruited and enrolled in 8 different cities spread across the US. The results of this actual use study indicate that: 1. 33.8% of the participants “started using” HeatSticks (i.e. ≥ 100 HeatSticks used) during the observational period, meaning that they were using the product on a continuous basis. 2. 32.7% of them “switched” (i.e. ≥ 70% of tobacco products (HeatSticks and CC) used were HeatSticks) from CC to HeatSticks showing that a sizeable proportion of participants adopted a usage behavior involving either exclusive or predominant use of HeatSticks. 3. 34.6% of the participants who “started using” HeatSticks had a “combined use” of CC and HeatSticks (i.e. >30% and <70% of products used were HeatSticks). While the proportion of “combined use” decreased over time, the proportion of “CC use” (32.7%) (i.e. ≤30% of products used were HeatSticks) increased, indicating that a substantial proportion of participants with “combined use” returned to CC. 4. 15.5% of the participants, who “started using HeatSticks and switched” to HeatSticks, “switched back” to CC. 5. There was no increase in the use of tobacco products between the baseline and the observational period. 6. The levels of misuse of THS were overall low suggesting that participants used the product as intended or designed.