Extended-release naltrexone is associated with a much lower rate of heroin relapse in men who have been released from jail, compared with released inmates addicted to heroin who are not given treatment, a new study concludes.

Extended-release naltrexone, sold under the brand name Vivitrol, blocks the effects of opioids such as heroin on the brain, Forbes reports. Vivitrol prevents relapse by reducing euphoria, pain relief, sedation, physical dependence and cravings. It is given as a monthly injection.

The study included 33 men who had been incarcerated by the New York City Department of Corrections. They did not want to participate in methadone or buprenorphine maintenance programs. Sixteen of the men received Vivitrol before they were released from jail, and were offered a second injection a month later. The other 17 inmates did not receive the drug.

Among those not given Vivitrol, 88 percent relapsed after being out of jail for a month, compared with 38 percent of those given the drug, the researchers report in Addiction.

Vivitrol can be expensive, the article notes. The retail cost is about $1,100 per dose. People with insurance coverage usually have a co-pay of up to $50 per dose. Medicaid costs for the drug vary depending on state plans.

“There has been a lot of interest in Vivitrol as post-incarceration relapse prevention, but not much actual data,” lead investigator Joshua Lee noted in a news release. “This randomized trial was designed to examine the impact of the medication on relapse to heroin in the first few weeks after release from jail, and it showed substantial benefits.”