In January 2016, the UK Government legislated for the blanket prohibition of ânew psychoactive substancesâ (NPS), i.e. unregulated substances that were viewed as similar to already controlled drugs. This followed a six-year period over which these substances have, with increasing speed, been scheduled as drugs, while the harms associated with these substances has increased. This thesis critiques policy here in terms of the way âNPSâ has been represented as a problem for policy makers. Drawing on post-structuralist theory and Science and Technology Studies, it seeks to account for first, how and in what ways these substances have been represented as a problem, and what other possibilities for thinking about NPS are silenced in these accounts. To explore this, the thesis undertakes a documentary analysis of the production of the NPS âproblemâ in the media, Parliament and technical and policy documents, alongside 19 interviews with participants who currently use, or had previously used, NPS. This thesis argues that NPS policy has enacted a limited framework for engaging with the risks of emerging drugs markets, which is primarily concerned with the threats these substances pose to those who believe they are safe due to being briefly legally available. In turn, the interview data indicates that participant in this market offer a range of distinct accounts of NPS, indicating the mixed results of regulation, the strategies deployed for addressing risks, the contexts in which harms accrue, and the capacity to experience the effects of these substances as beneficial and pleasurable. In comparing these accounts, it is argued that policy here constructs a limited account of the âpublic interestâ which excludes the interests and alternative perspectives of NPS users, who may offer different constructions of these objects and the appropriate goals of regulation. In turn, the thesis argues that critique should focus on the practices whereby the âpublic interestâ with which drug policy has to engage involves the exclusion of drug users from being able to participate in defining the nature of âNPS problemsâ. This exclusion has negative impacts for drugs users, in the sense of making drug markets more dangerous, but also limits the scope for thinking, in an inclusive way, about the goals contemporary drug policy might hope to achieve. In terms of future research, it is argued that drug policy is usefully critiqued in terms of how, to what extent and in what ways it constitutes drug users as part of the âpublicâ with which policy should be concerned. In the context of contemporary drug policy struggles in numerous countries, the mobilizations of the public undertaken here and their effects will be a matter of ongoing concern.