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

Aim To evaluate the effectiveness of the offer of Smoke Free – an evidence-informed, widely used app – for smoking cessation versus no support. Design Two-arm individually randomised controlled effectiveness trial. Setting Online with no restrictions on location. Participants 3,143 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 comparators Offer 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 measures The 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. Results The 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. Conclusions Among 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. ### Competing Interest Statement EB and JB have received unrestricted research funding from Pfizer, and JB only from J&J, who manufacture smoking cessation medications. RW has undertaken research and consultancy for and receives travel funds and hospitality from manufacturers of smoking cessation medications (Pfizer, GlaxoSmithKline and Johnson and Johnson). OP, RW, and JB are unpaid members of the scientific steering group of the Smoke Free mobile application. All authors declare no financial links with tobacco companies, e-cigarette manufacturers, or their representatives. ### Clinical Trial ISRCTN85785540 ### Clinical Protocols ### Funding Statement This study was funded by Cancer Research UK (PRCRPG-Nov21\100002). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethical approval for the trial was obtained from the UCL Research Ethics Committee (reference: CEHP/2020/579). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors