Abstract: We identified eight eligible studies reporting information about mass media smoking campaigns, one of which is new for this update. Seven of the studies used a controlled trial design and one an interrupted time-series analysis. Risks of bias were high across all included studies and there was considerable heterogeneity in study design, intervention and population being assessed.Three studies (n = 17,385), one of which compared a mass media intervention to no intervention and two of which evaluated mass media interventions as adjuncts to school-based interventions, found that the mass media interventions reduced the smoking behaviour of young people. The remaining five studies (n = 72,740) did not detect a significant effect on smoking behaviour. These included three studies comparing a mass media intervention to no intervention, one study evaluating a mass media intervention as an adjunct to a school-based intervention, and one interrupted time-series study of a social media intervention. The three campaigns which found a significant effect described their theoretical basis, used formative research in designing the campaign messages, and used message broadcast of reasonable intensity over extensive periods of time. However, some of the campaigns which did not detect an effect also exhibited these characteristics. Effective campaigns tended to last longer (minimum 3 years) and were more intense (more contact time) for both school-based lessons (minimum eight lessons per grade) and media spots (minimum four weeks' duration across multiple media channels with between 167 and 350 TV and radio spots). Implementation of combined school-based components (e.g. school posters) and the use of repetitive media messages delivered by multiple channels (e.g. newspapers, radio, television) appeared to contribute to successful campaigns. Certainty about the effects of mass media campaigns on smoking behaviour in youth is very low, due to inconsistency between studies in both design and results, and due to methodological issues amongst the included studies. It would therefore be unwise to offer firm conclusions based on the evidence in this review. Methodologically rigorous studies investigating the effect of social media and novel forms of technology as part of tobacco prevention campaigns for youth are needed.

Plain-language summary: We found eight studies out of 1326 publications, covering 52,746 participants. One of these studies is new to this updated version of the review. The most recent search was conducted in June 2016. All studies were directed at youth younger than 25 years. Seven studies were conducted in the USA and one was conducted in Norway. The mass media method (e.g. television) and certain characteristics of those taking part (e.g. age), as well as the length of time followed up, differed between studies. Three out of eight studies found that the intervention was effective in preventing smoking in youth. The remaining five studies did not detect an effect. Although there was some overlap in characteristics between both effective and ineffective programmes, effective campaigns tended to last longer (minimum 3 years) and were more intense (more contact time) for both school-based lessons (minimum eight lessons per grade) and media spots (minimum four weeks' duration across multiple media channels with between 167 and 350 TV and radio spots). Implementation of combined school-based components (e.g. school posters) and the use of repetitive media messages delivered by multiple channels (e.g. newspapers, radio, television) appeared to contribute to successful campaigns. The quality of studies in this review is limited, due to problems in reporting results and issues with study design. Studies varied in their design, the interventions they tested, and in the people they involved. Studies found mixed results. In particular, none of the studies reported blinding of groups and there were concerns around how the studies were allocated to intervention or control. It would therefore be unwise to offer firm conclusions based on the evidence in this review. Inclusion of only two studies from the last 10 years is concerning, particularly considering the rising use of social media among youth. More high-quality studies are needed.