A Cochrane review included 28 studies with over 16 000 smokers. Trials were conducted in 1 to 6 sessions, with the duration of each session ranging from 10 to 60 minutes. All but two of the trials used supportive telephone contacts, and supplemented the counselling with self-help materials. Interventions were delivered by primary care physicians, hospital clinicians, nurses or counsellors. Motivational interviewing (MI) versus brief advice or usual care yielded a modest but significant increase in quitting (RR 1.26, 95% CI 1.16 to 1.36; 28 trials, n=16 803). Subgroup analyses suggested that MI was effective when delivered by primary care physicians (RR 3.49, 95% CI 1.53 to 7.94; 2 trials, n=736) and by counsellors (RR 1.25; 95% CI 1.15 to 1.63; 22 trials, n=13 593). Both shorter (less than 20 minutes per session) and longer sessions were effective (RR 1.69, 95% CI 1.34 to 2.12; 9 trials, n=3 651 and RR 1.20, 95% CI 1.08 to 1.32; 16 trials, n=10 306 respectively). Both single session and multiple session treatments produced positive outcomes (RR 1.26, 95% CI 1.15 to 1.40; 16 trials, n=12 103 and RR 1.20, 95% CI 1.02 to 1.42; 11 trials, n=3 928; respectively). Evidence is unclear at present on the optimal number of follow-up calls.
Comment: The quality of evidence is downgraded by variable shortcomings in study quality.