We examined whether duration of electronic cigarette (e-cigarette) use could be associated with smoking reduction or cessation attempt.
5,409 current smokers at baseline enrolled in the French CONSTANCES cohort in 2015 or 2016 were included. Duration of e-cigarette use was categorized as follows: never; former user for more than one year; former user for less than one year; new user for less than one year; return to use for less than one year; regular use for one to two years; regular use for more than two years. Two outcomes were considered at one-year of follow-up: change in the number of cigarettes per day and cessation attempt.
Compared to never users, former users had an increase in the number of cigarettes per day at follow-up (B = 0.95[95%CI:0.57-1.33] and B = 1.03[95%CI:0.47-1.59] for former users of more than one year and less than one year, respectively). Compared to never users, all categories of current users had a decrease in the number of cigarettes per day (B = -3.31[95%CI:-4.07;-2.54] and B = -4.18[95%CI:-5.06;-3.29] for new users of less than one year and users of more than two years, respectively). Compared to never users, former users had a decreased likelihood of cessation attempt (OR = 0.80[95%CI:0.67-0.95] and OR = 0.77[95%CI:0.60-0.99] for former users of more than one year and less than one year, respectively). Compared to never users, all categories of current users had an increased likelihood of cessation attempt (OR = 3.12[95%CI:2.32;4.19] and OR = 3.36[95%CI:2.39;4.72] for new users of less than one year and users of more than two years, respectively).
E-cigarette use was associated with smoking reduction and cessation attempt for individuals who have used it for less than one year and additional benefits are expected to occur with a longer duration of use. Former users of e-cigarettes had poorer outcomes than those who have never used them.

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