Purpose
This paper aims to provide a practical tool to guide researchers in conducting drug research in prison, outlining the main research phases − preparation, methodological choices, implementation and ethical approval − as well as challenges and recommendations for each phase.

Design/methodology/approach
This paper is based on the experiences of implementing the European Questionnaire on Drug use among People Living in Prison, a model questionnaire developed by the European Union Drugs Agency, in some European countries.

Findings
During the research preparation, objectives, map of the prison system, understanding of legislation and context and key actors should be identified. A formal request should be sent to the prison authorities. Methodological decisions include choice of data collection tools, sampling strategies, implementation and dissemination. Flexibility is essential in implementation, while ensuring independence from prison staff. Adequate equipment, space and feedback to participants are recommended. Ethical approval is critical.

Research limitations/implications
This paper is based on the experience of some European countries, and other barriers and facilitators can be found in other contexts.

Practical implications
This paper describes the barriers to conduct research in prison and the possible solutions to overcome them, providing a practical tool to conduct ethical drug research in prison.

Social implications
This paper can have profound social implications helping researchers across Europe to identify health and social needs of this population.

Originality/value
This paper provides a unique insight for strategies to overcome challenges related to the implementation of ethical drug research in prisons, laying a foundation to support harmonised drug research in prison across countries.