Background This study examined the effects of the iPlayClean anti-doping intervention on attitudes towards doping and susceptibility, and whether delivery mode affected the results. Methods A total of 1081 high-level UK athletes (14-18 years old, 904 males, 177 females) were cluster-randomised to the control (11 teams/organisations/schools, 314 athletes), face-to-face group presentation (8 teams/organisations/schools, 254 athletes), online (11 teams/organisations/schools, 251 athletes), or face-to-face presentation with online access (5 teams/organisations/schools, 262 athletes). Results Compared to the control group, all modes of the iPlayClean anti-doping education programme reduced favourable attitudes towards doping immediately after the intervention, which was sustained across all intervention groups 8 weeks later. All delivery modes impacted doping susceptibility immediately after the intervention, in comparison to the control group, but the effects were only sustained for the face-to-face presentation group. Conclusion Contrary to findings within previous anti-doping interventions, we have shown that doping attitudes can be changed and that the results can be sustained across all modes of delivery, 8 weeks later. Research is required to assess for how long these changes are sustained, and how often anti-doping education should be delivered to high-level athletes to reinforce clean play values.Copyright © 2020 The Author(s). Published by Elsevier B.V. All rights reserved.