ORs and adjusted ORs of the association between e-cigarette use and subsequent combustible cigarette use for: (1) never-smokers at baseline, (2) non-smokers* (never or no current use) at baseline and (3) former smokers at baseline
| Authors/year | Country | Baseline cigarette use | E-cigarette use | Follow-up cigarette use | OR (95% CI) | Adjusted OR (95% CI) |
| Initiation in never smokers at baseline | ||||||
| Berry et al26 | USA | Never | Ever | Ever | 4.09 (2.97 to 5.63) | |
| Chien et al27 | Taiwan | Never | Ever | Ever | 2.44 (1.94 to 3.09) | 2.14 (1.66 to 2.75) |
| Conner et al47 | UK (England) | Never | Ever | Ever | 4.03 (3.33 to 4.88) | 2.78 (2.20 to 3.51) |
| McMillen et al50 | USA | Never | Current† | Ever | 16.4 (9.8 to 27.5) | 6.6 (3.7 to 11.8) |
| Pénzes et al46 | Romania | Never | Ever | Ever | 2.75 (1.52 to 4.96) | 3.57 (1.96 to 6.49) |
| Current use in non-smokers at baseline | ||||||
| Aleyan et al28 | Canada | Non-smokers* | Current† | Current† | Wave 1–2: 1.54 (1.37 to 1.74) | |
| Wave 2–3: 1.18 (1.08 to 1.29) | ||||||
| Barrington-Trimis et al48 | USA | Never | Current† | Current† | NHW to dual use: 7.44 (3.63 to 15.3) | |
| HW to dual use: 3.64 (1.62 to 8.18) | ||||||
| Bold et al45 | USA | No current* | Current† | Current† | Wave 1–2: 7.08 (2.34 to 21.42) | |
| Wave 2–3: 3.87 (1.86 to 8.06) | ||||||
| Conner et al47 | UK (England) | Never | Ever | Current† | 3.38 (2.72 to 4.21) | 2.17 (1.76 to 2.69) |
| Regular‡ | 3.60 (2.35 to 5.51) | 1.27 (1.17 to 1.39) | ||||
| Kinnunen et al29 | Finland | Never | Ever nicotine-containing | Daily | 11.52 (4.91 to 27.01) | 8.50 (2.14 to 29.19) With school clustering: 2.92 (1.09 to 7.85) |
| Ever non-nicotine containing | 1.88 (0.25 to 14.45) | 2.50 (0.25 to 12.05) With school clustering: 0.94 (0.22 to 4.08) | ||||
| McMillen et al50 | USA | Never | Ever (not current) | Established§ | 5.9 (1.7 to 20.7) | 2.5 (0.6 to 10.9) |
| Current† | 25.5 (10.6 to 61.4) | 8.0 (2.8 to 22.7) | ||||
| Osibogun et al49 | USA | Non-smokers* | Current† | Regular‡ | Year 1: 16.4 (7.8 to 34.5) | Year 1: 5.0 (1.9 to 12.8) |
| Year 2: 11.1 (3.5 to 35.2) | Year 2: 3.4 (1.0 to 11.5) | |||||
| Relapse in former smokers at baseline | ||||||
| Brose et al30 | UK | ≥2-month ex-smokers | Ever | Ever | 1.52 (0.88 to 2.62) | 1.13 (0.61 to 2.07) |
| Non-daily | 3.32 (1.23 to 8.96) | 2.45 (0.85 to 7.08) | ||||
| Dai and Leventhal51 | USA | >12-month ex-smokers | Current† | Ever | 6.36 (4.49 to 9.00) | 2.00 (1.25 to 3.20) |
| Occasional | 5.79 (1.50 to 22.33) | 1.56 (0.34 to 7.14) | ||||
| Prior | 9.68 (4.74 to 19.75) | 3.77 (1.48 to 9.65) | ||||
| McMillen et al50 | USA | ≥5 years ex-smokers | Ever (not current†) | Ever | 5.4 (2.9 to 10.2) | 3.3 (1.6 to 6.7) |
| Current† | 7.6 (3.0 to 19.4) | 5.2 (1.6 to 16.3) | ||||
*Non-smokers defined as never or no current (past 30-day) use.
†Current defined as past 30-day use.
‡Regular defined as ≥20 days/30 days.
§Established defined as ≥100 combustible cigarettes and currently smokes every day or some.
HW, Hispanic white; NHW, non-Hispanic white.