Naltrexone has been shown to be clinically effective in treating opioid dependence, although there are reports that it may be unsafe in treatment of unselected cases. Although there are no generally accepted pharmacological treatments for crack cocaine addiction alone, there is evidence that naltrexone can be useful in cases of concurrent cocaine and heroin use. In 2005 Bristol Specialist Drug Service initiated a naltrexone treatment programme targeted at pre-release offenders using both crack cocaine and heroin. Of 172 referrals, only 51 (30%) were inducted into treatment, and only 16% of these were retained at 3 months, and 4% at 9 months. There was evidence to support induction in prison, as 90% of those who were inducted there continued treatment on release. An integrated approach between criminal justice and community services is of primary importance in getting users into treatment. Interviews highlighted that the environment outside of prison can trigger relapse, and that community clinics need to separate clients on an abstinence programme from those who continue to use. Of clients interviewed, 52% reported that they use heroin to mitigate severe come down from crack, and it is suggested that naltrexone may be of use for these specialized combined users.