Background: Opioids are currently widely used to manage chronic non-malignant pain, but there is a growing concern about harm resulting from opioid misuse, and the need for medicine optimisation, in which pharmacists could potentially play a key role.Objective: This study seeks to identify challenges to community pharmacists’ role in optimizing prescribed opioids for Chronic Non-Malignant Pain (CNMP).Setting: Community pharmacies in the UK.Method: Semi-structured interviews based on the Theoretical Domains Framework were conducted with 20 community pharmacists recruited through professional networks and analysed thematically.Result: Pharmacists perceive themselves as guardians of patients’ welfare and aspire to contribute to prescribed opioid optimisation. However, they are challenged by the lack of relevant training, inadequate time and resources, infrastructural and systemic constraints (such as repeat prescribing and prescription delivery services, lack of access to medical records and information about diagnosis), personal factors, including communication with doctors, and relationship with patients.Conclusion: The role of community pharmacists in optimising chronic opioid therapy is neither well-defined nor implemented in the UK. Utilisation of their potential skills and knowledge in this area requires an appropriate training curriculum, tackling the infrastructural and systemic constraints, support and resources to facilitate pharmacists’ engagement in patient monitoring and education. The findings in this study can contribute to inform policy makers with potentials to enhance pharmacists’ role in opioids therapy optimisation and, hence, ensure patients' safety when using prescribed opioids.