In October 2021, a majority of the UK gambling industry implemented a new UK safer gambling message, ‘take time to think’, which features on gambling advertising and websites. An effective safer gambling message could plausibly affect several relevant gambling behaviours, with previous research suggesting that message effectiveness is maximised via messages that are displayed prominently immediately prior to gambling. We experimentally tested this message's effect on four contemporaneous gambling behaviours (the proportion of available funds bet, clicks for help service information, the mean speed of play, and the total number of roulette spins made) in an incentivised online roulette game in a sample of UK-based online gamblers. Participants (n = 2,305) were randomly allocated to either (a) ‘no-message’ control, (b) ‘message’ shown throughout the condition or (c) a ‘message+’ condition, where the message was shown throughout and also via a popup immediately prior to the roulette game. Overall, the results showed no credible effects across the four outcome measures when comparing either of the message conditions to the no-message control. Even the prominent display of the ‘take time to think’ message did not lead to credible beneficial effects on a range of contemporaneous gambling behaviours.