Device Characteristics of Long Term Electronic Cigarette Users: A Follow-Up Study.

At follow-up, 83.6% of participants were continued users while 16.4% of users stopped e-cigarette use between baseline and follow-up. Stoppers were significantly younger than continuers (37.6 years vs 40.3 years, p=0.0390). Of the 458 users who answered questions regarding other tobacco use, 86.9% were exclusive e-cigarette users and 13.1% were dual users of e-cigarettes and other products. Of the 77 participants who quit e-cigarettes and answered questions on other tobacco use, 31.2% still used other tobacco products and 68.8% quit all tobacco products.
At baseline, 24.2%, 26.4%, and 49.4% of participants were cigalike, advanced, and mod device users, respectively, while at follow-up, 6.5% of participants were cigalike users, 24.7% were advanced users, 52.4% were mod users, and 16.4% quit using e-cigarettes. Baseline cigalike users were the most likely to stop use of e-cigarettes (cigalike 31.8% stopped v. advanced 14.9% stopped v. mod 9.6% stopped, p < 0.01) between baseline and follow-up. Compared to continuers, participants who stopped using e-cigarettes reported significantly lower nicotine concentrations at baseline (13.1 mg/ml vs 15.3 mg/ml, p = 0.0137); significantly higher use of tobacco/menthol flavored e-liquid (57.6% vs. 39.4%, p = 0.0085); significantly lower prevalence of using a tank system (33.0% vs 60.3%, p<0.0001); and significantly higher report of 100% PG liquid (20.0% vs 8.7%; p = 0.0125). Significant predictors of quitting e-cigarette use between baseline and follow-up including lower e-cigarette device cost (OR = 0.993; 95% CI: = 0.988-0.998), not utilizing a tank system for liquid (OR=0.488, 95% CI=0.281–0.846), lower nicotine concentration (OR=0.949; 95% CI=0.917-0.982), use of a device without variable voltage (OR=0.541; 95% CI 0.310-0.946) and lower age (OR=0.967; 95% CI 0.949-0.986).
Among participants who continued using an e-cigarette between baseline and follow-up, the mean Penn State Electronic Cigarette Nicotine Dependence Index (PSECDI) score was 8.2 (SD = 3.9), mean use of 21.1 times per day (SD = 25.5), a mean use of 28.6 days (SD = 4.9) of the last 30-days), and had a mean overall use of 4.8 years (SD = 14.3). Compared with baseline, continued users at follow-up were significantly less likely to report a preferred liquid flavor of tobacco or menthol (32.5% vs 38.8%, p<0.0001); reported lower mean nicotine concentration (7.6 mg/ml vs 15.3 mg/ml, p<0.0001); more likely to use a tank system (74.0%vs 60.3%, p<0.0001); less likely to report 100% PG liquid (0.3% vs 5.7%, p<0.0001), less likely to report 100% VG liquid (4.1% vs 10.1%, p=0.0035); and significantly more likely to report a combination of PG and VG (95.6% vs 84.1%, p<0.0001). Among continued users, 21.1% used <25% PG; 28.1% used 25-49% PG; 46.8% used 50-75% PG; 4.0% used >75% PG. The authors concluded that "[c]ontinuers were likely to transition to devices with more advanced features, like variable voltage, and to reduce the nicotine concentration of their liquid. Baseline cigalike users were the most likely to stop using their e-cig and return to use of other tobacco products" (p. 5).

Yingst, J., Foulds, J., Veldheer, S., & Du, P. (2019). Device Characteristics of Long Term Electronic Cigarette Users: A Follow-Up Study. Addictive Behaviors, 91, 238-243.