Pain and opioid use disorder (OUD) are inextricably linked, as the former can be a risk factor for the development of the latter, and over a third of persons with OUD suffer concomitant chronic pain. Assessing pain among people with OUD is challenging, be-cause ongoing opioid use brings changes in pain responses and most pain assess-ment tools have not been validated for this population. In this narrative review, we discuss the fundamentals of pain assessment for populations with OUD. First, we de-scribe biological, psychological, and social aspects of the pain experience among people with OUD, as well as how opioid-related phenomena and healthcare dispari-ties in this population may contribute to the pain experience. Second, we review meth-ods to assess pain including: (1) traditional self-reported methods, such visual analog scales, and structured questionnaires; (2) behavioral observations and physiological indicators; (3) and laboratory-based approaches, such as functional brain imaging, electroencephalography, and quantitative sensory testing. These methods are consid-ered from a perspective that encompasses both pain and OUD. Finally, we discuss strategies for improving pain assessment in persons with OUD and implications for future research, including educational strategies for multidisciplinary teams. Substan-tial gaps persist in our knowledge, particularly regarding the applicability of current pain assessment methods to persons with OUD, as well as the generalizability of the existing results from adjacent populations. As research linking pain and OUD evolves, considering the needs of diverse populations with complex psychosocial back-grounds, we will be better equipped to reduce these gaps.

The rise of psychedelics in contemporary medicine has sparked interest in their potential therapeutic applications. While traditionally associated with countercultural movements and recreational use, recent research has shed light on the potential benefits of psychedelics in various mental health conditions. In this review, we explore the emerging role of psychedelics in the management of chronic pain and opioid use disorder (OUD), two critical areas in need of innovative treatment options. Pain control remains a significant clinical challenge, particularly for individuals with OUD and those who receive long-term opioid therapy (LTOT) who develop marked tolerance to opioid-induced analgesia. Despite the magnitude of this problem, there is a scarcity of controlled studies investigating pain management alternatives for these populations. Drawing from preclinical and human evidence, we highlight the potential of psychedelics to act on shared neurobiological substrates of chronic pain and opioid use disorder, potentially reversing pain- and opioid-induced neuroadaptations, such as central sensitization. We elaborate on the multifaceted dimensions of the pain experience (sensory, affective, and cognitive) and their intersections that overlap with opioid-related phenomena (opioid craving and withdrawal), hypothesizing how these processes can be modulated by psychedelics. After summarizing the available clinical research, we propose mechanistic insights and methodological considerations for the design of future translational studies and clinical trials, building on a shared clinical and neurobiological understanding of chronic pain and OUD. Our intention is to provide timely perspectives that accelerate the development and exploration of novel therapeutics for chronic pain and OUD amidst the escalating opioid crisis.