There is a lot of research suggesting that the drug naltrexone blocks the action of heroin in the body yet its clinical usefulness has proved limited. This could be because many people are reluctant to take the drug or start taking it and then stop. Longer-lasting injections of naltrexone could get around some of these difficulties. Preliminary studies have been encouraging and a study of 56 heroin addicts by researchers in Norway has also proved promising. The group was divided into two with half receiving the long-lasting naltrexone and half receiving the usual treatment for heroin addicts. Those participants who received naltrexone had, on average, 45 days less heroin use than the other participants. The naltrexone stayed in the participants' bloodstreams throughout the study. Unfortunately two patients in the control group (but none among those taking naltrexone) died during the course of the study.
Kunoe, Nikolaj ... [et al] - Naltrexone implants after in-patient treatment for opioid dependence: randomised controlled trial British Journal of Psychiatry June 2009, 194(6), 541-546