Naltrexone (Vivitrol) is a medicine that blocks the effects of opioids.  Like naloxone (Narcan), it can stick on opioid receptor molecules and prevent heroin and other opioids from attaching, thus blocking them from exerting any of their typical effects.  If a patient is taking naltrexone and uses heroin, they will not get any effect.  Unfortunately, most people will not take naltrexone pills regularly when they are using it for opioid addiction, but the extended-release injection (Vivitrol shot) helps this problem because someone can take the shot and it will last for a month at a time.

After naltrexone was developed for treating opioid addiction, people realized it also helps reduce alcohol use.  Now naltrexone pills and the Vivitrol shot are both used for alcohol problems as well as opioid problems.

Naltrexone has not been compared in a direct head-to-head clinical trial to buprenorphine (Suboxone), but they are both known to be effective treatments for opioid addiction.  Suboxone is usually easier to get started on because patients have to be off of all opioids for 7 days or longer if they are transitioning onto naltrexone, and it is usually hard to wait that long without using again due to withdrawals and strong cravings.