The benefits and studies of

Low-dose Naltrexone (LDN)

How it works, summary of mechanism of action, side effects, contraindications, and clinical research.

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Naltrexone is often classified as an opiate antagonist. However, at low-doses, Naltrexone acts to inhibit certain inflammatory pathways, which involve Toll-Like Receptors (TLRs). Naltrexone’s traditional use is in treating addiction to opiate drugs, such as heroin or morphine, or to treat acute overdose of these opioids. The daily dose of Naltrexone used for this purpose is usually between 50 mg (moderate dose naltrexone) to 300mg (high dose Naltrexone).

In the USA, Low-dose Naltrexone (LDN) has been used for the treatment of autoimmune diseases since 1985. Although LDN has used at low-dosages for many years by patients with autoimmune disorders, the occurrence of significant introductory-effects of LDN, as well as long-term side-effects of LDN, have not been extensively studied. A widely used LDN dosage protocol was first developed in the 1980s by the late Dr. Bernard Bihari, who was qualified in Neurology, Internal Medicine, and Psychiatry.


LDN is most commonly being used for Chronic Fatigue, Multiple Sclerosis (MS), autoimmune diseases, thyroid conditions, and various cancers. Many autoimmune diseases seem to respond to LDN. Low-Dose Naltrexone is known to be a potent antagonist to certain opioid receptors, as well as a wide range of inflammation-mediating Toll-Like Receptors (e.g. TLR4, TLR7/8/, TLR9).

It is important to emphasize that Naltrexone (the drug in LDN prescriptions) is produced in a 50:50 mixture of two different chemical shapes (called isomers). It has been recently discovered that one chemical-isomer binds to immune cells, whilst the other chemical isomer binds to opioid receptors. Although having the same atomic composition, the two chemical-isomers of Naltrexone have quite different therapeutic activities.

The LEVO (left-handed) version of Naltrexone blocks opiate receptors. The DEXTRO (right-handed) version blocks receptors on immune cells. These include “Toll-Like Receptors” (TLRs), which are heavily involved in immunity. LDN is a potent antagonist of TLR-4, as well as an antagonist of TLR7/8 and TLR-9 (ref 10).

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Taking Naltrexone in larger doses of 50-300mg seems to negate the immunomodulatory effect by overwhelming the opioid receptors. The Naltrexone dose must be in the range of 0.5mg, usually maxing out its benefit at 4.5mg in clinical experience. However, some individuals experience positive clinical effects at lower doses, others at higher doses than 4.5mg.

Levo-Naltrexone is an antagonist for the Opiate/Endorphin receptors

  • This causes increased Endorphin release
  • Increased Endorphins modulate the immune response
  • This reduces the speed of unwanted cells growing

Dextro-Naltrexone is an antagonist for at least one, if not more immune cells

  • Antagonises “TLR,” thereby suppressing cytokine modulated immune system
  • Antagonises TLR-mediated production of NF-kB – thereby reducing inflammation, potentially down-regulating oncogenes


Many patients who start LDN do not experience any severe side effects. Some patients may see an increase in symptoms when first starting LDN therapy. In Multiple Sclerosis (MS), this can be characterized by increased fatigue, or increased spasticity. In Chronic Fatigue Syndrome (CFS/ME), this can be the onset of apparent flu-like symptoms. LDN can cause sleep disturbances if taken at nighttime – this is most likely because of the increase in endorphin release. These disturbances can take the form of vivid dreams, or insomnia.

In various studies (and anecdotal accounts), the number of T-Lymphocytes has been shown to dramatically increase when a patient starts on LDN. This may account for some of the benefits patients feel when they are being treated for an autoimmune disease, or cancer. This has not been directly evidenced in Multiple Sclerosis.

Clinical experience shows that in less than ten percent of cases treated, increased introductory symptoms may be more severe or more prolonged than usual, lasting sometimes for several weeks. Rarely, symptoms may persist for 2-3 months before the appropriate beneficial response is achieved.

If side effects are troublesome, then reducing dose by 50% for 7 days, before increasing it again, is a good idea.

Rarely, some patients experience gastrointestinal (GI) side effects, such as nausea and or constipation/diarrhea. The reason for this is currently unknown. The side effects may be due to the presence of large numbers of delta-opiate receptors in the intestines. Patients experiencing GI side-effects can request LDN Sublingual Drops, which transfer the LDN directly into the bloodstream – avoiding the GI tract.

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Over the past 15 years, there has been a strong growing body of research on the efficacy of Low-Dose Naltrexone therapy in many disease states.

There are currently over 580 LDN research articles, papers, and case studies on PubMed.

See the table below for more information about LDN and a specific condition.


Print out this Patient-Prescriber LDN Leaflet and take it to your prescriber to help start the conversation about LDN as a treatment option.

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