BackgroundAntibiotic resistance is an ongoing pandemic which represents a global public health threat. To encourage the judicious use of antibiotics, public health discourse and campaigns often engage in threat-based messaging depicting an apocalyptic post-antibiotic future. We studied the effectiveness of the strategy because of mixed evidence for its success, and because it is unclear how experiencing the COVID-19 pandemic might have influenced it.MethodsWe conducted a randomised controlled trial with 378 participants in three waves (before and during the pandemic in 2021 and 2022). Participants were randomly allocated to either the baseline arm, featuring a control film, or the intervention arm featuring a short film, Catch, depicting a post-antibiotic future. Participants expressed expectations and intended requests for antibiotics for a hypothetical ear infection and their adherence to a prescribed antibiotic for a hypothetical kidney infection. In waves 2 and 3, they also reported any COVID-19-related changes to their antibiotic desires.ResultsShowing participants a film about a post-antibiotic future substantially lowers clinically inappropriate expectations for antibiotics and their intended requests. Participants report that the experience of the COVID-19 pandemic decreased their desire for antibiotics but only when they watched the intervention film. The intervention slightly decreases participants’ adherence intentions towards a prescribed antibiotic treatment.ConclusionsPresenting a film about an apocalyptic post-antibiotic future lowers expectations and intended requests for antibiotics and therefore has the potential to encourage judicious use of them. However, the adverse effects of such messaging on adherence to a course of antibiotics should be proactively managed.