Effectiveness of the offer of the Smoke Free smartphone application compared with no intervention for smoking cessation: a pragmatic randomised controlled trial

AimTo evaluate the effectiveness of the offer of Smoke Free - an evidence-informed, widely used app - for smoking cessation versus no support. DesignTwo-arm individually randomised controlled effectiveness trial. SettingOnline with no restrictions on location. Participants3,143 adult smokers (74.7% female; mean[SD] age 49.0 [11.5] years) motivated to make a quit attempt in the next month, recruited between August-2020 and April-2021. Interventions and comparatorsOffer of the Smoke Free app plus follow-up (intervention arm) versus no intervention plus follow-up (comparator arm). Both groups were shown a brief message at the end of the baseline questionnaire encouraging them to make a quit attempt. Main outcome measuresThe primary outcome was self-reported 6-month continuous abstinence assessed 7 months after randomisation. Secondary outcomes included quit attempts in the first month post-randomisation, 3-month continuous abstinence assessed at 4 months, and 6-month continuous abstinence at 7 months among those who made a quit attempt. The primary analysis was performed on an intention-to-treat basis, with missing-equals-smoking imputation. Sensitivity analyses included i) restricting the intervention group to those who took up the offer of the app, ii) using complete cases, and iii) using multiple imputation. ResultsThe effective follow-up rate for 7 months was 41.9%. The primary analysis showed no evidence of a benefit of the intervention on rates of 6-month continuous abstinence (intervention 6.8% vs. comparator 7.0%; RR=0.97, 95%CI=0.75-1.26). Analyses on all secondary outcomes also showed no evidence of a benefit. Similar results were observed on complete cases and using multiple imputation. When the intervention group was restricted to those who took up the offer of the app (n=395, 25.3%), participants in the intervention group were 80% more likely to report 6-month continuous abstinence (12.7% vs. 7.0%; RR=1.80, 95%CI=1.30-2.45). Equivalent subgroup analyses produced similar results on the secondary outcomes. These differences persisted after adjustment for key baseline characteristics. ConclusionsAmong motivated smokers provided with very brief advice to quit, offer of the Smoke Free app did not have a detectable benefit for cessation compared with follow-up only. However, the app increased quit rates when smokers randomised to receive the app downloaded it.