Anti-tobacco policy in schools: upcoming preventive strategy or prevention myth? A review of 31 studies.

To summarise the evidence on effectiveness of school anti-tobacco policies (exposure) in preventing tobacco use (outcome) among high school students.The search was conducted between 1 September and 30 November 2011 on six electronic databases with keywords: 'policy', 'ban', 'restriction' and 'environment' in combination with 'adolescent' or 'student', 'school' and 'smoking' in titles, abstracts or keywords. Restrictions were made to articles published in English.Studies were included if they targeted the relevant grades/age; reported at least one outcome measure of students' ever or current tobacco use; reported on the effects of exposure to policy separately from other interventions. Inclusion criteria were assessed independently by two of the coauthors. Of 2723 articles initially identified, 31 articles met the inclusion criteria (1.1\%).Independent multiple observers extracted the data following the GRADE system guidelines to classify the level of evidence in relation to the review objective.Studies were very heterogeneous in the definitions of exposure to school anti-tobacco policy and of tobacco use, adjustment for potential confounders and reporting of results, therefore summary quantitative measures of effect were not calculated. Qualitative summary statements were derived by reviewing the results reported in text and tables for distinct policy constructs. Evidence could be classified as low or very low, resting on cross-sectional studies with high risk of bias. Studies were rather consistent in indicating that comprehensive smoking bans, clear rules, strict policy enforcement, availability of education and prevention were associated with decreased smoking prevalence. Formally adopted and written policies, surveillance of students' behaviour and presence/severity of sanctions were not consistently associated to students' tobacco use.The evidence concerning the effectiveness of a school policy alone in preventing youth tobacco use is weak and inconclusive. Experimental studies or observational studies with longitudinal design are warranted, employing clear definitions of policy components and careful control for confounding.