AbstractBackground and AimsTobacco smoking remains the leading cause of preventable death and disease worldwide. Digital interventions delivered through smartphones offer a promising alternative to traditional methods, but little is known about their effectiveness. Our aim was to determine the effectiveness of Quit Genius, a novel digital therapeutic intervention for smoking cessation.DesignTwo-arm, single-blinded, parallel-group randomized controlled trialSettingReferrals from primary care practicesParticipants556 Adult smokers (aged ≥ 18 years), smoking at least five cigarettes a day for the past year. 530 were included for the final analysis.Intervention and comparatorDigital therapeutic intervention for smoking cessation consisting of a smartphone application delivering cognitive behavioral therapy content, one-to-one coaching, craving tools and tracking capabilities. The control intervention was Very Brief Advice along the Ask, Advise, Act model. All participants were offered nicotine replacement therapy for three months. A random half of each arm was assigned a carbon monoxide (CO) device for biochemical verification.MeasurementsThe primary outcome was self-reported seven-day point prevalence abstinence at four-weeks post quit date.Findings556 participants were randomized (treatment n=277, control n=279). The intention-to-treat analysis included 530 participants (n=265 in each arm; 11 excluded for randomization before trial registration, and 15 for protocol violations at baseline visit).At four weeks post-quit date, 45% of participants in the treatment arm had not smoked in the preceding seven days, compared to 29% in control (risk ratio 1.55 [1.23, 1.96], p = 0.0002; intention-to-treat, n=530). Self-reported seven-day abstinence agreed with CO measurement (CO <10 ppm) in 96% of cases (80/83) where CO readings were available. No harmful effects of the intervention were observed.ConclusionsThe Quit Genius digital therapeutic intervention is a superior treatment in achieving smoking cessation four weeks post quit date compared to very brief advice.