The authors explain that drug use in prisons in the United Kingdom is more prevalent than it is in the general population. Mental health problems are also more abundant in prisons than in the general population. However, while mental health problems usually plague offenders before they end up in prison, many inmates experiment with drugs for the first time in prison. The authors of this paper set out to identify the characteristics of inmates who had ever used heroin or cocaine versus the characteristics of inmates who first used these drugs while in prison. The authors also examined the relationship between mental health problems and substance abuse. Data from a cross-sectional survey of all prisons in England or Wales were used to examine the characteristics of 3,142 prisoners. Data included personal demographics, social history, psychiatric morbidity, and drug use. Findings revealed that more than 60 percent of heroin users reported that they used heroin while in prison. More than 25 percent of heroin users claimed they first used the drug while in prison. The authors show how heroin or cocaine use is related to a prisoner’s experience of prison. In conclusion, the authors note that programs designed to curb heroin initiation in prison is needed as part of a culture-wide effort to reduce substance abuse. Tables, references