Co-designing polysubstance use harm reduction messaging with and for young adults: findings from a participatory, intersectional citizen jury and community survey (The ‘Vibe Check’ Project)

Abstract Background Polysubstance use is highly prevalent among young adults, yet harm reduction research has traditionally excluded their meaningful involvement. The Vibe Check Project aimed to meaningfully involve young adults with lived/living experience of polysubstance use to identify key polysubstance use harms and best-practice digital harm reduction strategies using a participatory, peer-led approach. Methods This two-phase study included: (1) a cross-sectional online survey (March–June 2025) of 81 young adults (aged 18–30, living in NSW) who had used more than one psychoactive drug concurrently in the past year; and (2) a 7-hour online citizen jury with a randomly selected subset (n = 8) of survey participants. Survey items were co-developed with a peer researcher and Youth Advisory Board, and comprised quantitative and qualitative questions on polysubstance use patterns, motivations, and harm perceptions. Jurors were tasked with deliberating and reaching consensus on two domains: 1) the main harms arising from polysubstance use among young adults, 2) the best ways for leveraging digital, online, and social media platforms to address these. Quantitative data were analysed descriptively in RStudio, and qualitative survey responses and citizen jury transcripts were analysed using summative content and deductive thematic analysis in NVivo. Results Survey responses indicated that interaction effects between drugs were the most concerning harm for young adults. Citizen jurors reached unanimous consensus on three key harms: (1) balancing self-reflection and peer dynamics in the face of unclear and unpredictable drug effects (2) navigating life after polysubstance use, particularly comedowns and poor decisions made under impaired judgement; and (3) unintended, undesirable development of tolerance and/or dependence. Jurors also unanimously recommended digital harm reduction should be educational, practical, brief, engaging, and accessible, championing diverse lived/living experiences through partnership with trusted, reputable community sector organisations, rather than social media influencers. Conclusions This is the first known study to use a citizen jury with young adults to address polysubstance use harms. The participatory, peer-led approach generated youth-driven, consensus-based recommendations for digital harm reduction in practice. Findings emphasise the important role of planning and self-reflection, the double-edged sword of peers and peer influence, and partnerships with trusted community sector organisations for effective polysubstance use harm reduction.