INTRODUCTION Contact interventions have shown short-term effectiveness in reducing stigmatising attitudes and behaviours of the public towards marginalised population groups, including people who inject drugs. We theorised that the effectiveness of an intervention differs according to peoples' underlying social values and undertook a study to test this.

METHODS We recruited participants from the Australian public by social media and measured their attitudes, desire to maintain personal distance, and support for structural stigma towards people who inject drugs before and after a brief online video intervention (n = 314). We divided participants into tertile groups according to their responses to a conservatism scale and compared group differences in post-intervention stigma scores (n = 242-244), controlling for pre-intervention scores and demographic variables.

RESULTS Adjusting for baseline levels, the post-intervention scores in all measures showed significant improvement but scores of the moderate group were consistently most improved. Stigmatising attitudes in the moderate group were significantly reduced when compared with the conservative and progressive groups. However, reductions in desire for personal distance and support for structural stigma did not significantly differ by conservatism group.

DISCUSSION AND CONCLUSIONS A brief online contact intervention showed immediate effectiveness in reducing stigma towards people who inject drugs. As people with moderate values were found to be more amenable to changing their perspectives, audience social values may need consideration when designing and evaluating stigma interventions. More research is needed to understand how to influence people with more conservative values, and how to increase public support for policies and practices that reduce stigma.