BACKGROUND AND AIMS Tobacco smoking represents a major cause for preventable death and morbidity. Results from non-randomized studies suggest that smoking cessation therapy in a residential setting might be a new viable way to facilitate smoking abstinence. We aimed to test the effects of residential multicomponent group therapy for smoking cessation compared with outpatient group therapy.

DESIGN Prospective parallel-group open-label randomized superiority trial, with assessments at baseline, 6 and 12 months.

SETTING Recruitment throughout Germany via media advertisements.

PARTICIPANTS Adult smokers (≥10 cigarettes/day) randomly assigned to residential (n = 157) or outpatient (n = 158) therapy. 51.8% female; mean age 53.2 years; mean years of smoking 34.4.

INTERVENTION AND COMPARATOR Residential 9-day smoking cessation group therapy comprising six daily therapy sessions and supportive interventions for cessation and daily structure embedded in the routines of a somatic rehabilitation center, compared with weekly outpatient smoking cessation group therapy (3-7 weeks) provided in routine care courses close to the participants' places of residence, both including at least 9 h of behavioral therapy.

MEASUREMENTS Co-primary outcomes were self-reported continuous 6- and 12-month abstinence (hierarchically ordered). Primary analyses were conducted in the therapy-uptake population including participants who started therapy with sensitivity analyses in the intention-to-treat population of all randomized participants.

FINDINGS Intervention uptake rates were 87.3% (n = 137) in the residential and 60.1% (n = 95) in the outpatient group. In the therapy-uptake population, abstinence rates were 46.7% in the residential versus 26.3% in the outpatient group at 6 months (odds ratio [OR] = 2.46, 95% confidence interval [CI] = 1.39-4.33, P = 0.0019) and 39.4% versus 24.2% at 12 months (OR = 2.04, 95% CI = 1.14-3.64, P = 0.017). Biochemically validated abstinence rates at 12 months were 33.1% in the residential versus 17.4% in the outpatient group (OR = 2.35, 95% CI = 1.22-4.51, P = 0.011). In the intention-to-treat population, self-reported and biochemically validated abstinence rates at 12 months were 34.4% in the residential versus 14.6% in the outpatient group (OR = 3.08, 95% CI = 1.77-5.34, P < 0.0001) and 28.6% versus 10.3% (OR = 3.48, 95% CI = 1.85-6.52, P = 0.0001), respectively.

CONCLUSIONS Residential therapy exclusively for smoking cessation is feasible and effective and could be a beneficial new treatment for smokers.