Naltrexone: An Opioid Blocker That Gets Around

Naltrexone (brand names include Vivitrol and ReVia) blocks opioid receptors just like Narcan (naloxone), which is used to treat opioid overdoses. Both drugs prevent any opioids in the vicinity From being able to latch onto opioid receptors and do their opioid thing. While Narcan and fast- and short-acting, naltrexone works more slowly and is longer-acting.  It’s available as a once-daily pill or as a monthly injection. It’s FDA approved for use in addictions, but it’s also been used off-label in quite a wide range of other conditions.

Addictions

Not surprisingly, naltrexone can be used to treat opioid addiction. However, it really gets around, and it can be used in a number of other conditions, suggesting that our body’s natural opioid system is probably busier than we might think.

Naltrexone can be used for alcoholism, even though alcohol doesn’t act at opioid receptors. It’s also been used for dextromethorphan (the DM in cough syrup) dependence.

Mental health-related uses

There have been a few case studies published of naltrexone being helpful for compulsive sexual behaviour and kleptomania.

A number of studies have found positive results in PTSD with co-occurring alcohol use disorder. There is also some indication that naltrexone may have some effectiveness as an add-on treatment for PTSD without alcoholism.

Naltrexone has been used for dissociative disorders, including dissociative identity disorder. It’s also shown some effectiveness for dissociation and self-injury in borderline personality disorder (BPD). The exact link to the opioid system is unclear.

A small pilot study showed positive results from adding naltrexone for breakthrough symptoms of major depressive disorder in people who were already on a particular set of medications. I didn’t come across any follow-up studies.

Pain disorders

There’s been some research to suggest that at lower than standard doses, naltrexone can have an anti-inflammatory effect that targets a number of different inflammatory and immune mediators in the body as well as microglial cells in the brain. Calming down microglia could, at least theoretically, help to reduce neuropathic (nerve) pain.

Some studies have shown that naltrexone can decrease pain in fibromyalgia. Fibromyalgia is thought to have a neuro-immune component, which may explain how naltrexone is helpful.

In multiple sclerosis, there is some evidence that it can improve energy and quality of life.

There are some early indications of efficacy in Crohn’s disease, diabetic neuropathy, and chronic lower back pain, but there isn’t enough research yet to give a clear indication as to whether it actually works for these conditions.

Other

The combination of naltrexone and the antidepressant bupropion (brand names Contrave, Mysimba) is used for obesity, with each component decreasing appetite by a different mechanism.

Why the diverse uses?

While there are quite a few drugs that do multiple different things, naltrexone is interesting in terms of how disconnected some of these uses seem at first glance. Then again, there are also connections.

Compulsive behaviours and addictions seem like they would logically share elements of underlying mechanisms. If you consider that the body’s natural opioid system responds to pain, and dissociation may be a defense strategy in certain types of painful situations, the link to naltrexone seems plausible.

Then there’s the anti-inflammatory element. There seems to be a steadily growing body of evidence that inflammation places a fundamental role in a wide variety of conditions. Science really needs to find a way for us to flick a switch to tell our bodies’ inflammatory systems to calm the f*** down.

In the meantime, we’ve got naltrexone.

References

• Mischoulon, D., et al. (2017). Randomized, proof-of-concept trial of low dose naltrexone for patients with breakthrough symptoms of major depressive disorder on antidepressants. Journal of Affective Disorders, 208(2017), 6-14.
• Moghaddas, A., et al. (2017). The potential role of naltrexone in borderline personality disorder. Iranian Journal of Psychiatry, 12(2), 142-146.
• Pape, W. & Wöller, W. (2015). Low dose naltrexone in the treatment of dissociative symptoms. Der Nervenarzt, 86(3), 346-351.
• Patten, D.K., Schultz, B.G., & Berlau, D.J. (2018). The Safety and Efficacy of Low-Dose Naltrexone in the Management of Chronic Pain and Inflammation in Multiple Sclerosis, Fibromyalgia, Crohn’s Disease, and Other Chronic Pain Disorders. Pharmacotherapy, 38(3), 382-389.
• Wikipedia: Naltrexone