How Does Naltrexone Work to Treat OUD?
Naltrexone is an opioid antagonist that saturates opioid receptors in the brain, which prevents individuals from experiencing the euphoric effects of drugs like heroin or fentanyl. It is essentially a “blocker” that prevents a person from getting high or potentially overdosing if they use opioids after taking this medication. In contrast to Methadone and Suboxone, it is NOT an opioid agonist and therefore doesn’t reduce actual cravings or withdrawal symptoms. For these reasons, it does not always work as effectively as Suboxone or Methadone for OUD, but can be considered as an alternative to Methadone or Suboxone in patients who cannot tolerate Suboxone or Methadone.
What Forms Does Naltrexone Come In?
Naltrexone most commonly is prescribed in either pill or monthly injectable form (brand name “Vivitrol).
However, for certain individuals, it may be an option to receive the medication in an “implant” form. This form can be implanted under the skin by a qualified medical professional and usually lasts for up to six months at a time.
While most people can access and use pills or monthly injections of Naltrexone, some individuals who have trouble taking a daily medication or a monthly injection might be good candidates for an implant which lasts up to six months.
How Does the Naltrexone Implant Work?
A naltrexone implant is surgically implanted under a patient’s skin in a fairly noninvasive procedure. The implant then works by slowly administering naltrexone at a steady rate without a patient needing to monitor their naltrexone use or otherwise take it on a daily basis.
How Effective is Naltrexone Implant for OUD Compared to Pills or Monthly Injections?
Naltrexone implants are quite new, and evidence on their efficacy is limited both in terms of quantity and quality at this time.
With that said, there is promising limited evidence that naltrexone implants may help in the treatment of OUD similarly to that of pill or injectable forms 
People struggling with multiple substance disorder or other limitations such as poor social support may have difficulty taking daily Naltrexone pills. The main advantage of implants is that patients don’t have to remember to take naltrexone daily as they would with pills, so compliance is greatly improved [4, 5, 6]. The implant is always there and the patient does not need to do anything in order to ensure they get their daily medication. 
How Effective is Naltrexone Implant for OUD Compared to Suboxone or Methadone?
Very few studies have looked at the effectiveness of the Naltrexone implant compared to buprenorphine/naloxone (Suboxone) and methadone. Most studies that have compared Naltrexone to Suboxone or Methadone have looked at oral or injectable forms of Naltrexone, not implants. We can therefore only extrapolate the efficacy of a Naltrexone implant as compared to the pill or injectable forms that have been more studied.
In general, Naltrexone for OUD as compared to Suboxone and Methadone is less effective because it prevents overdose but does not actually address the cravings and withdrawal symptoms that drive most people to continued opioid misuse. Both Suboxone (buprenorphine) and methadone have been called “essential medicines” by the World Health Organization for the treatment of OUD. While Naltrexone is an alternative treatment option for patients who cannot tolerate Suboxone or Methadone, it is not the first line treatment for OUD.
Overall, Naltrexone implants are understudied, and more needs to be done comparing them to alternative options. However, these implants also seem to have helped at least some people overcome their struggles with substance use disorder. Some studies show implants comparing favorably to oral alternatives primarily due to increased compliance.
Who Is a Candidate for a Naltrexone Implant?
Any person who has an opioid use disorder is a candidate for Naltrexone, although as explained above, Suboxone and Methadone are still considered the most efficacious treatments available. Naltrexone is also used for alcohol use disorder and therefore it may be a good option for patients who are struggling with both misuse of alcohol and opioids.
Overall, implants may work well for those who would benefit from naltrexone but struggle with treatment compliance or cannot take pills or injectable forms of the medication for whatever reason.
Patients should speak to a medical professional who specializes in addiction treatment to see if the implant is a good fit for their needs.
By Elena Hill, MD, MPH
Elena Hill, MD; MPH received her MD and Masters of Public Health degrees at Tufts Medical School and completed her family medicine residency at Boston Medical Center. She is currently an attending physician at Bronxcare Health Systems in the Bronx, NY where ... Read More
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- Naltrexone. Substance Abuse and Mental Health Services Administration. https://www.samhsa.gov/medication-assisted-treatment/medications-counseling-related-conditions/naltrexone. April 2022. Accessed July 2022.
- Naltrexone for Opioid Use Disorders: A Review of Clinical Effectiveness, Cost-Effectiveness, and Guidelines. CADTH Rapid Response Report: Summary With Critical Appraisal. https://www.ncbi.nlm.nih.gov/books/NBK525041/. July 2014. Accessed July 2022.
- Slow Release Naltrexone Implant vs Oral Naltrexone for Improving Treatment Outcomes in Opioid Addicted Participants with HIV: A Placebo-Controlled Randomised Trial. The Lancet HIV. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6529232/. March 2019. Accessed July 2022.
- Implantable Naltrexone for Opioid Dependence. Boston University. https://www.bu.edu/aodhealth/2009/07/01/implantable-naltrexone-for-opioid-dependence/. 2009. Accessed July 2022.
- Effective Treatments for Opioid Addiction. National Institute on Drug Abuse. https://nida.nih.gov/publications/effective-treatments-opioid-addiction. November 2016. Accessed July 2022.
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