Potential harm from universal school-based mental health interventions: Candidate mechanisms and future directions.

Universal school-based mental health interventions involve lessons delivered to whole classes of young people irrespective of need, with the overall aim of improving mental health literacy, preventing mental health problems and/or reducing those that have already started. A number of high-quality trials show that universal interventions can have a range of negative effects, with participants in the intervention group experiencing worsening mental health or other negative outcomes. In this review, we summarise what we know so far about these negative effects, which we refer to as 'potential harm'. Two important questions remain poorly understood. First, the mechanisms driving potential harm are unknown, including whether negative effects are driven by reporting phenomena, the content of the intervention itself, or both. Second, individual differences in susceptibility to these effects is unclear. In the second half of the paper, we explore whether further universal trials should be run and argue that, if they are, the crucial issue of negative effects must be considered at all stages. In particular, we recommend that trials be designed in such a way to test mechanisms and individual differences in response. Information can then be provided to schools and policymakers about why young people might respond in different ways to an intervention, and how to support vulnerable students. Ultimately, this will lead to more effective and less harmful interventions for everyone.