A Cochrane review included 41 trials with over 13 000 young people. Complex theoretical model with stage of change, motivational interviewing, cognitive behavioural therapy and/or social cognitive theory was effective compared to control (RR 1.40, 95% CI 1.14 to 1.74; 9 trials, n=2827). There was evidence of an intervention effect for group counselling (RR 1.35, 95% CI 1.03 to 1.77; 9 trials, n=1910), but not for individual counselling (RR 1.07, 95% CI 0.83 to 1.39; 7 trials, n=2088), mixed delivery methods (RR 1.26, 95% CI 0.95 to 1.66; 8 trials, n=2755) or the computer or messaging interventions (pooled RRs between 0.79 and 1.18, 9 studies in total). Neither of the pharmacological intervention trials achieved significant results, but both were small-scale, with low power to detect an effect.
Another Cochrane review included 41 trials with over 33 000 participants. Stage-based self-help systems demonstrated a benefit for the staged groups compared to any standard self-help support (RR 1.27, 95% CI 1.01 to 1.59; 6 trials, n=5947) or compared to 'usual care' or assessment-only (RR 1.32, 95% CI 1.17 to 1.48; 12 trials, n=7596). 13 trials of stage-based individual counselling vs any control condition gave an RR of 1.24 (95% CI 1.08 to 1.42). However, in quite low quality trials directly comparing the same intervention in stage-based and standard versions no clear advantage for the staging component was found.
Comment: The quality of evidence is downgraded by limitations in study quality (e.g. no verification of smoking status) and inconsistency (heterogeneity in interventions and outcomes).