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e-liquid. None of the subjects used nicotine free e-liquids. The study population was dominated by individuals who prepared e-liquids themselves: 66.7% of e-cigarette users and 74.1% of dual users (Table 1). Over half (52.7%) of the e-cigarette users (53.6% of exclusive e-cigarette users and 51.9% dual users; p = 0.9) had chosen devices that allow technical modifications of the e-cigarette such as voltage, power, and resistance of the heater. Almost all exclusive e-cigarette users (96%) had ever tried cigarette smoking. Out of the 60 e-cigarette users, 18.5% initiated nicotine use by e-cigarette. E-cigarette, as a first nicotine product, was declared by 16% of exclusive e-cigarette users and 20.7% of dual users (p = 0.6). The most common reasons stated for starting to use e-cigarettes were it being less harmful to health, price, and desire to quit traditional smoking. The reasons stated for using e-cigarettes are presented in Figure 1. Figure 1. Motivations for e-cigarette use. Int. J. Environ. Res. Public Health 2019, 16, 2279 4 of 10 Table 1. Patterns and habits of e-cigarette use among e-cigarette users and dual users. Overall n = 60 Exclusive E-Cigarette Users n = 30 Dual Users n = 30 p * Average concentration of nicotine in the e-liquid [mg/mL] Mean ± SD 7.5 ± 3.8 6.8 ± 3.4 8.3 ± 4.0 0.1 Median (min–max) 6.0 (2–18) 6.0 (2–12) 6.0 (3–18) Milliliters of e-liquid used per day [mL] Mean ± SD 4.2 ± 3.4 4.1 ± 3.9 4.3 ± 3.1 0.8 Median (min–max) 3.0 (0.15–15) 3.0 (0.3–15) 3.5 (0.15–10) Milliliters of e-liquid used per month [mL] Mean ± SD 107 ± 102.2 113.9 ± 121.2 100.5 ± 81.9 0.6 Median (min–max) 90.0 (10–550) 90.0 (10–550) 70.0 (10–300) Type of e-liquid used Purchased in the store % (95%CI) 29.6 (19.1–42.8) 33.3 (18.6–52.2) 25.9 (13.2–44.7) 0.6 Self-prepared % (95%CI) 70.4 (57.2–80.9) 66.7 (47.8–81.4) 74.1 (55.3–86.8) Number of different models of e-cigarette (device) used Mean ± SD 4 ± 4 3.6 ± 3.3 4.3 ± 4.6 0.5 Median (min–max) 3 (1–23) 3 (1–17) 3 (1–23) Legend: 95%CI, 95-percent confidence interval; min–max, minimum and maximum value range; * results of U Mann-Whitney test. Dual users who were actively smoking both types of cigarettes (traditional and e-cigarette) indicated that traditional cigarette smoking offers more smoking satisfaction (46.2%) compared to using e-cigarettes (23%). Also, smoking a cigarette in a group of friends, in combination with a cup of coffee, after a meal, or after sex was associated with a greater subjective feeling of satisfaction compared to the feelings associated with the use of an e-cigarette in the same situations. Dual users indicated that the smell (92.9%) and the taste (82.1%) of e-cigarettes as well as the subjective feeling associated with the inhalation and exhalation of vapor generated from e-cigarettes were the primary advantages of e-cigarettes over traditional cigarettes. 3.2. Fagerstrom Scores and Levels of Nicotine Addiction The average FTND score among exclusive e-cigarette users was over twice as high (mean 3.5 versus 1.6) as among traditional cigarette smokers (p = 0.002; Table 2). The mean nicotine dependence level from e-cigarettes (mean 4.7) was higher than that from traditional cigarettes (mean 3.2; p = 0.03) among dual users. E-cigarette users were more likely to use an e-cigarette in the first 30 min after waking and were more likely to find it difficult to refrain from using e-cigarettes in places where it is forbidden (Table 2). Int. J. Environ. Res. Public Health 2019, 16, 2279 5 of 10 Table 2. Aspects of cigarette and e-cigarette smoking based on Fagerström test for nicotine dependence (FTND). Smokers n = 30 % (95%CI) Exclusive E-Cigarette Users n = 30 % (95%CI) Dual Users n = 30 % (95%CI) p How soon after waking up do you reach for a cigarette? Within 30 min 17.9 (7.9–35.6) 42.3 (25.5–61.1) 0.04 After 30 min 82.1 (64.4–92.1) 57.7 (38.9–74.5) How soon after waking up do you reach for an e-cigarette? Within 30 min 53.9 (35.5–71.2) 57.1 (39.1–73.5) 0.8 After 30 min 46.1 (28.8–64.5) 42.9 (26.5–60.9) Do you find it difficult to refrain from smoking in places where it is forbidden? Yes 10.7 (3.7–27.2) 19.2 (8.5–37.9) 0.4 No 89.3 (72.8–96.3) 80.8 (62.1–91.5) Do you find it difficult to refrain from use e-cigarette in places where it is forbidden? Yes 34.6 (19.4–53.8) 42.9 (26.5–60.9) 0.5 No 65.4