Evidence
CAnimal replicated
Key risks
LDN (1.5-4.5 mg/day) has a consistently excellent safety profile across all trials. Most commonly reported side effect: vivid dreams or sleep disturbance (typically transient, first 1-2 weeks; resolved by timing the dose in the morning rather than at night). No serious adverse events attributable to LDN reported in RCTs. No organ toxicity. No addiction liability. No withdrawal. No dependence. The safety profile is one of the most favorable of any prescription drug used for chronic conditions.
Two Drugs, One Molecule
The most important concept in this chapter. Standard naltrexone (50 mg) and LDN (1.5-4.5 mg) are the same chemical compound used at doses so different that they produce fundamentally different pharmacological profiles. At standard dose: sustained opioid receptor blockade, used for addiction. At low dose: brief blockade, endorphin rebound, microglial modulation, anti-inflammatory — used for neuroinflammatory and autoimmune conditions. They are not related versions of the same treatment. They are different treatments that use the same molecule at different doses.
FDA-Approved Indications (50 mg)
Opioid Use Disorder (OUD): prevents opioid euphoria; used as part of MAT (medication-assisted treatment) alongside counseling. Alcohol Use Disorder (AUD): reduces alcohol craving; standard dose 50 mg/day oral. Extended-release injectable form (Vivitrol, 380 mg IM monthly): for OUD and AUD with adherence advantages. NOT approved for LDN uses: fibromyalgia, MS, Crohn's, Long COVID, ME/CFS, autoimmune conditions, general immune optimization.
LDN — Off-Label Indications (Evidence-Based)
Fibromyalgia: strongest LDN evidence; multiple RCTs; 2024 Lancet Rheumatology trial (n=100, 6 mg, DBRPCT — significant pain improvement). Multiple Sclerosis: Cree 2010 (DBRPCT, n=60 — improved quality of life, MSFCS). Crohn's Disease: Smith 2007 (open-label pilot positive); subsequent small RCTs mixed. Long COVID/ME-CFS: emerging evidence; several pilot studies positive; systematic review 2025 preliminary. Complex Regional Pain Syndrome (CRPS): pilot data positive. Depression: one pilot trial positive. These are all off-label uses requiring physician supervision and compounding pharmacy preparation.
The Commercial Absence Problem
Naltrexone is a generic drug. Patent-expired. No pharmaceutical company has commercial incentive to fund the Phase 2/3 trials needed to establish LDN for new FDA-approved indications — the cost of trials exceeds the revenue from a generic drug. This explains why the LDN evidence base consists mostly of small investigator-initiated trials rather than industry-funded Phase 3 programs. The absence of large trials does NOT necessarily indicate absence of efficacy. It may reflect the economics of generic drug development. This context is essential for interpreting the evidence.
Why a small molecule
Naltrexone is a small molecule, It is included in this reference because: (1) it is commonly used by the same community that uses peptides for immune optimization, longevity, autoimmune conditions, and chronic inflammation; (2) it acts on the endogenous opioid system, which overlaps with mechanisms relevant to multiple peptide compounds; (3) its inclusion provides the complete picture of the neuroinflammatory and immunomodulatory toolkit.