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(46.2–80.6) 57.1 (39.1–73.5) Which cigarette would you hate most to give up? The first one in the morning 57.1 (39.1–73.5) 73.1 (53.9–86.3) 0.2 Any other 42.9 (26.5–60.9) 26.9 (13.7–46.1) Which e-cigarette would you hate most to give up? The first one in the morning 30.8 (16.5–50.0) 35.7 (20.7–54.2) 0.7 Any other 69.2 (50.0–83.5) 64.3 (45.8–79.3) How many cigarettes per day do you smoke? 10 or less 85.7 (68.5–94.3) 69.2 (50.0–83.5) 11 to 20 14.3 (5.7–31.5) 23.1 (11.0–42.1) 0.2 21–30 0.0 (0.0–11.3) 7.7 (2.1–24.1) 31 or more 0.0 (0.0–11.3) 0.0 (0.0–11.3) How many times a day do you use e-cigarettes? (Number of e-smoking sessions: one e-smoking session consist of 15 puffs or approximately 10 min of use) 10 or less 38.5 (22.4–57.5) 32.1 (17.9–50.7) 11 to 20 38.5 (22.4–57.5) 35.7 (20.7–54.2) 0.8 21–30 11.5 (4.0–28.9) 10.7 (3.7–27.2) 31 or more 11.5 (4.0–28.9) 21.4 (10.2–39.5) Do you smoke more frequently during the first hours after waking than during the rest of the day? Yes 14.3 (5.7–31.5) 34.6 (19.4–53.8) 0.08 No 85.7 (68.5–94.3) 65.4 (46.2–80.6) Do you use e-cigarettes more frequently during the first hours after waking than during the rest of the day? Yes 15.4 (6.2–33.5) 39.3 (23.6–57.6) 0.05 No 84.6 (28.8–64.5) 60.7 (42.4–76.4) Int. J. Environ. Res. Public Health 2019, 16, 2279 6 of 10 Table 2. Cont. Smokers n = 30 % (95%CI) Exclusive E-Cigarette Users n = 30 % (95%CI) Dual Users n = 30 % (95%CI) p Do you smoke if you are so ill that you are in bed most of the day? Yes 21.4 (10.2–39.5) 42.3 (25.5–61.1) 0.09 No 78.6 (60.5–89.8) 57.7 (40.0–74.5) Do you use e-cigarettes if you are so ill that you are in bed most of the day? Yes 34.6 (19.4–53.8) 67.9 (49.3–82.1) 0.01 No 65.4 (46.2–80.6) 32.1 (17.9–50.7) FTND summary score FTND cigarette score: mean ± SD 1.6 ± 1.6 3.2 ± 2.2 0.002 * FTND e-cigarette score: mean ± SD 3.5 ± 2.6 4.7 ± 2.6 0.03 ** 95%CI indicates the 95% Confidence Interval; p indicates the result of the U Mann-Whitney test; * indicates the result of the U Mann-Whitney test for smokers versus exclusive e-cigarette users; ** indicates the result of the U Mann-Whitney test for cigarettes versus e-cigarettes among dual users. 4. Discussion The results of our study allow us to characterize patterns of use of e-cigarettes among young adults in Poland who are experienced users of e-cigarettes. Almost one-fifth of the participants initiated nicotine use bye-cigarette. Most subjects started e-cigarette use due to health-related (harm reduction or for smoking cessation) or financial reasons. The participants consumed relatively large amounts of nicotine-containing e-liquid (almost half a bottle per day). More than half of the participants chose technically advanced e-cigarette devices. Our key finding was that nicotine dependence levels measured with FTND were over two times higher among exclusive e-cigarette users (mean 3.5) compared to traditional tobacco smokers (mean 1.6; p < 0.001). Similarly, among dual users, nicotine dependence levels were higher when using an e-cigarette (mean 4.7) compared to a traditional cigarette (mean 3.2; p = 0.03). The high levels of nicotine dependence observed among young adult e-cigarette users compared to smokers in our study suggest this group may be at high risk of addiction. We also found that dual users used e-liquids with higher concentrations of nicotine and consumed more milliliters of e-liquid per day compared to exclusive e-cigarette users. These findings together with the higher mean FTND score suggests a higher nicotine dependence level in this group of e-cigarette users. However, by contrast exclusive e-cigarette users presented with a longer duration of e-cigarette use (on average 1.3 months longer) compared to dual users, although this was not statistically significant. Our findings contrast with results obtained by González et al. [28], Etter et al. [23], and Liu et al. [29]. In a study conducted by González et al., e-cigarette users scored lower in FTND (mean 4.38) than cigarette smokers (mean 5.57; p = 0.03) [28]. Etter et al. concluded that e-cigarettes are less addictive than tobacco cigarettes and their addictive potential is comparable to nicotine gums [23], although they also found that users of nicotine-containing e-cigarettes presented higher