AbstractBackgroundHealthcare workers perform clinical behaviours which impact on patient diagnoses, care, treatment and recovery. Some methods of supporting healthcare workers in changing their behaviour make use of social norms by exposing healthcare workers to the beliefs, values, attitudes or behaviours of a reference group or person. This review aimed to evaluate evidence on (i) the effect of social norms interventions on healthcare worker clinical behaviour change and (ii) the contexts, modes of delivery and behaviour change techniques (BCTs) associated with effectiveness.MethodsSystematic review and meta-analysis of randomised controlled trials. Searches were undertaken in seven databases. The primary outcome was compliance with a desired healthcare worker clinical behaviour and the secondary outcome was patient health outcomes. Outcomes were converted into standardised mean differences (SMDs). We performed meta-analyses and presented forest plots, stratified by five social norms BCTs (social comparison,credible source,social reward,social incentiveandinformation about others’ approval). Sources of variation in social norms BCTs, context and mode of delivery were explored using forest plots, meta-regression and network meta-analysis.ResultsCombined data from 116 trials suggested that social norms interventions were associated with an improvement in healthcare worker clinical behaviour outcomes of 0.08 SMDs (95%CI 0.07 to 0.10) (n= 100 comparisons), and an improvement in patient health outcomes of 0.17 SMDs (95%CI 0.14 to 0.20) (n= 14), on average. Heterogeneity was high, with an overallI²of 85.4% (healthcare worker clinical behaviour) and 91.5% (patient health outcomes).Credible sourcewas more effective on average, compared to control conditions (SMD 0.30, 95%CI 0.13 to 0.47,n= 7).Social comparisonalso appeared effective, both on its own (SMD 0.05, 95%CI 0.03 to 0.08,n= 33) and with other BCTs, and seemed particularly effective when combined withprompts/cues(0.33, 95%CI 0.22 to 0.44,n= 5).ConclusionsSocial norms interventions appeared to be an effective method of changing the clinical behaviour of healthcare workers and have a positive effect on patient health outcomes in a variety of health service contexts. Although the overall result is modest and variable, there is the potential for social norms interventions to be applied at large scale.Trial registrationPROSPEROCRD42016045718.