In this field note we describe the steps followed in the process of recruiting participants for the experimental drug prescription program in Andalusia (PEPSA). This trial is a comparative, randomized, open study of the difference between intravenous heroin treatment and oral methadone for socially excluded, opiate-dependent patients, in whom other available treatments have been unsuccessful. Because this is a hidden and hard-to-reach population, a specific approach was planned to put as many patients as possible in touch with the program. A previous study of the target population's distribution in the City of Granada was performed and the city was divided into three areas. Potential participants were interviewed in squares, soup kitchens and methadone dispensaries by outreach workers and peers, who suggested they make an appointment with a PEPSA physician. Peer-driven intervention was a crucial instrument in this recruitment procedure, allowing greater access to the target population. Furthermore, this approach allowed contact with drug users who do not attend health and social services. The work of the outreach team involved educating these users in harm reduction and offering them health and social alternatives beyond the clinical trial.