["Addiction, Volume 121, Issue 5, Page 1306-1315, May 2026. ", "\nAbstract\n\nBackground and aims\nExtensive critique of the evidence‐based policy paradigm has led to new ways of considering the role of evidence; for example Katherine Smith suggests that “ideas” rather than evidence mediate “the relationship between research and policy”. In this paper, we used Smith's typology on “ideas” to explore how this can be applied to a case of Australian policy making: a police diversion scheme for simple possession of drugs. We aimed to analyse the idea's journey into policy in one Australian jurisdiction (New South Wales) and assess its fit with the four different types of ideas outlined by Smith.\n\n\nMethod\nQualitative case study analysis using data from New South Wales, Australia, over the period 2018 to 2024. Multiple data sources were used: interviews with stakeholders (n = 26), documents [reports, non‐governmental organization (NGO) advocacy documents], media and official reports of a Drug Summit. Each data source was searched for narration/text concerned with police diversion in addition to decriminalisation, extracted and analysed against Smith's typology.\n\n\nResults\nFeatures of ‘institutionalised ideas’ suggest that police diversion is not an institutionalised idea. It appears in this case to be a ‘chameleonic idea’ inasmuch as its characteristics change and are malleably deployed by different stakeholders with different interests. ‘Flexian policy actors’ (including police, government officials, advocates and researchers) are able to interpret, transform and shape the meaning of police diversion to suit their interests and commitments. Despite evidence synthesis and expert review recommending police diversion as a second‐best option to decriminalisation, it was taken up into policy. We suggest this is because of its chameleonic nature, serving simultaneously at the hands of different policy actors as a roadblock to decriminalisation and as a Trojan horse for decriminalisation reform whilst also obscuring tensions between police diversion and decriminalisation.\n\n\nConclusions\nApplying Katherine Smith's typology of ideas to an Australian police diversion scheme for simple possession of drugs shows that the scheme is not an institutionalised idea but rather a chameleonic idea. Smith's typology of ideas adds another layer to policy process frameworks, enhancing analysis seeking to understand the uptake of ideas into policy.\n\n"]