Purpose: There is a strong political imperative to regard the prison as a key social setting for health promotion, but evidence indicates that drug misuse continues to be a significant issue for many prisoners. This paper aims to examine the social and environmental factors within the setting that influence individuals' drug taking. Design/methodology/approach: Focus groups and interviews were conducted with prisoners and staff in three male training prisons in England. The sampling approach endeavoured to gain "maximum variation" so that a broad based understanding of the prison setting could be gathered. The data were analysed in accordance with Attride-Stirling's thematic network approach. Findings: The findings suggest a myriad of social and environmental factors influencing drug use. While staff recognised the scale of the drugs problem, they struggled to cope with creative inmates who were not perturbed by taking risks to gain their supplies. Fellow prisoners played a major role in individuals' decision making, as did the boredom of institutional life and Mandatory Drug Testing (MDT) policies within the institutions. Practical implications: Drug treatment is an essential component of prison healthcare, but it only forms a small part of creating a health-promoting setting. If the health-promoting prison is to be fully realised, a more radical, upstream and holistic outlook is required. Originality/value: The settings approach is an important theoretical and practical approach in health promotion. In comparison to other settings (such as schools), however, there has been limited research on the prison as a health-promoting environment.