E-cigarette support for smoking cessation: Identifying the effectiveness of intervention components in an online randomised optimisation experiment

Aims: To determine which combination(s) of five e-cigarette-orientated intervention components, delivered online, affect smoking cessation. Design: A balanced five-factor (2x2x2x2x2=32 intervention combinations) randomised factorial design guided by the Multiphase Optimisation Strategy (MOST). Setting: Online (UK). Participants: 1214 eligible participants (61% female; 97% white) recruited via social media. Interventions: The five online intervention components designed to help smokers switch to exclusive e-cigarette use were: 1: tailored device selection advice; 2: tailored e-liquid nicotine strength advice; 3: tailored e-liquid flavour advice; 4: brief information on relative harms; 5: text message (SMS) support. Measurements: The primary outcome was 4-week self-reported complete abstinence at 12 weeks post randomisation. Primary analyses were intention-to-treat (loss to follow-up recorded as smoking). Logistic regressions modelled the 3-way and 2-way interactions and main effects, explored in that order. Findings: In the adjusted model, the only significant interaction was a 2-way interaction, advice on flavour combined with text message support, which increased the odds of abstinence (odds ratio = 1.55 [95% confidence interval = 1.13-2.14], p = 0.007, Bayes factor =7.25). There were no main effects of the intervention components. Conclusions: Text-message support with tailored advice on flavour is a promising intervention combination for smokers using an e-cigarette in a quit attempt