Naltrexone is an opioid antagonist medication that works by blocking the effects of opioids. Patients taking naltrexone receive a monthly injection, which reduces cravings for heroin/opioids and also blocks the brain’s opioid receptors from the patient feeling any euphoric effects should they impulsively use heroin. Naltrexone cannot be administered to a patient until he or she has been totally withdrawn from opioids (a procedure known as detoxification) and has been opioid-free for at least 7 days. Naltrexone prevents relapse and can also be used by patients who have been in treatment and have tapered off buprenorphine as an added protection against relapse.