Comment: Evidence of the range and magnitude of gambling-related harm is improving, highlighting the need for effective interventions. High quality evaluations of interventions to reduce harm in gambling studies are rare.1 In their study, Philip Newell and colleagues2 contribute important evidence from their randomised, online experimental study that evaluated behavioural responses to a high profile safer gambling campaign in the UK: “When the fun stops, stop”. This message is widely deployed, but has been criticised (eg, by Gambling with Lives) for asserting that gambling is fun and that individuals are responsible for keeping it that way.3 Newell and colleagues found that exposure to the safer gambling message during realistic online gambling tasks did not reduce the willingness of experienced gamblers to bet nor the amount they bet, relative to control participants. The authors detected some evidence of a potential so-called backfire effect in their study, noting that this safer gambling slogan might represent a dark nudge,4 rather than a harm minimisation intervention....