Low-dose naltrexone (LDN)

01Key questions

02Overview

Low-dose naltrexone (LDN) is the off-label use of naltrexone — a competitive opioid receptor antagonist FDA-approved at 50–100 mg/day for opioid use disorder and alcohol use disorder — administered at about a tenth of that (published studies mostly used 1–5 mg/day, most often 4.5 mg) to achieve anti-inflammatory, immunomodulatory, and analgesic effects through mechanisms distinct from its primary opioid-blocking action.

LDN is widely prescribed by integrative and functional medicine practitioners for fibromyalgia, ME/CFS, Crohn's disease, multiple sclerosis, complex regional pain syndrome (CRPS), various autoimmune conditions, and increasingly Long COVID. It is not FDA-approved for any of these indications. Naltrexone itself is generic and inexpensive; no commercial sponsor has funded large Phase 3 trials for LDN, which is the principal reason the evidence base remains modest.

03Mechanism of Action

LDN acts through several non-mutually-exclusive pathways, distinct from the high-dose opioid blockade used in addiction medicine:

• Opioid Growth Factor Receptor (OGFr) antagonism — Transient blockade of OGFr (the receptor for opioid growth factor / met-enkephalin) appears to promote cell proliferation and tissue repair. First characterized in intestinal epithelial and cancer-cell models.
• Toll-Like Receptor 4 (TLR4) modulation — LDN antagonizes TLR4 signaling on microglia and other innate immune cells, reducing production of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) and attenuating microglial activation in the CNS.
• Transient opioid receptor antagonism → rebound — Brief nightly blockade of μ-opioid receptors is hypothesized to cause a compensatory upregulation of endogenous opioids (β-endorphin, met-enkephalin) and increased opioid receptor expression.
• TRPM3 ion channel restoration — Mechanistic studies suggest LDN may restore TRPM3 channel function, with downstream effects on calcium signaling in sensory neurons. Mechanism inferred from indirect data.
• Hormesis-like dose response — Beneficial effects emerge only at low doses; standard opioid-blocking doses do not produce these immunomodulatory benefits.

04Evidence Separation

Crohn's Disease (Tier 2)

• Pilot open-label (2007) — PMID 17222320 — Smith JP et al. Am J Gastroenterol 2007;102(4):820–828. Mean CDAI dropped significantly (p=0.01); 89% response rate, 67% remission. Most common AE: sleep disturbance (n=7). No laboratory abnormalities.
• Randomized placebo-controlled trial (2011) — PMID 21380937 — Smith JP, Bingaman SI, Ruggiero F, Mauger DT, Mukherjee A, McGovern CO, Zagon IS. Dig Dis Sci 2011;56(7):2088–2097. doi 10.1007/s10620-011-1653-7. NCT00663117. Penn State College of Medicine. Double-blind, placebo-controlled, 12-week primary endpoint with pseudo-crossover (all patients received open-label LDN for 3 additional months). Primary outcome: ≥70-point CDAI reduction at 12 weeks; secondary: endoscopic mucosal healing with biopsy. LDN-treated subjects showed significant CDAI improvement and histological reversal of inflammation; placebo-armors did not.
• Evidence grade: Modest but consistent across pilot + RCT from a single investigative team. Limitations: small n, single center, unblinded follow-on phase, lack of independent replication in large RCTs.

Multiple Sclerosis (Tier 3)

• Small pilot trials and observational reports (e.g., Cree et al., 2010 — secondary progressive MS) suggest symptomatic benefit (fatigue, pain, quality of life), but no large confirmatory RCT.
• Mechanism hypotheses (TLR4 microglial modulation) biologically plausible but unproven for MS disease modification.

Fibromyalgia (Tier 3)

• Multiple small RCTs and observational series (e.g., Younger et al., 2013) suggest reductions in pain, fatigue, and inflammatory cytokines. Sample sizes small; effect sizes moderate; independent replication limited.

ME/CFS (Tier 3)

• Observational cohorts (e.g., Bolton et al.) report symptom improvement in subsets of patients. No RCT-grade evidence.

Long COVID / Post-COVID-19 Condition (Tier 3, evolving)

• Systematic review (May 2025) — Byambasuren et al., medRxiv 2025 (Bond University, Institute for Evidence-Based Healthcare). Reviewed published and registered studies up to May 2025. Findings:
• 0 RCTs identified.
• 4 pre–post observational studies, n=155 total.
• Pooled Hedges' g (negative = improvement):
• Fatigue: g = −0.74 (moderate)
• Brain fog: g = −0.53 (moderate)
• Sleep: g = −0.xx (moderate, magnitude not captured in source)
• Author conclusion: "While current research is not conclusive a therapeutic trial of LDN in Long COVID is reasonable and safe and can improve fatigue, sleep, pain, brain fog and daily function at doses of 1–6 mg/day."
• Evidence grade: Preliminary. Effect sizes encouraging but biased by uncontrolled pre–post design (regression to the mean, placebo effect, natural history of Long COVID all confound).

Other Investigated Indications (Tier 3, limited)

• Complex regional pain syndrome (CRPS)
• Hailey-Hailey disease, psoriasis, hidradenitis suppurativa, rheumatoid arthritis (dermatology/autoimmune small series)
• Gulf War Illness (small trials)

05Preclinical / Mechanistic

• OGFr antagonism demonstrated in intestinal epithelial cells, neuroblastoma, and animal colitis models.
• TLR4 modulation on microglia reduces pro-inflammatory cytokine release in vitro and in animal models of neuroinflammation.
• Animal colitis models (DSS-induced) showed that intermittent low-dose naltrexone reduced bowel inflammation and improved inflammatory index (precedent for Crohn's RCTs).
• Cancer biology: OGFr pathway explored as a target in pancreatic and other cancers; high-dose naltrexone + chemotherapy combinations investigated. Distinct from LDN; do not conflate.

06Uses

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07Safety Profile

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08Regulatory & Commercial Landscape

• Pricing: Naltrexone generic, ~$0.30–$1/day at LDN doses; specialty compounding $30–$100/month.
• LDN Research Trust, LDN Science — patient advocacy and information hubs.
• Claims audit: Cannot claim "cures" or "treats" FDA-unapproved indications. Permitted language: investigational; small-trial/observational data; off-label use.

09Evidence Summary Table

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What studies and practitioners report

Amounts as reported in the cited sources: trial doses with the population studied, and practitioner-reported ranges marked as such. Not medical advice.

• Trial 4.5 mg/day · LDN women with fibromyalgia, n=31 PMID 23359310
• Trial 4.5 mg/day · LDN adults with active Crohn's disease PMID 42701992
• Trial 0.1 mg/kg (max 4.5 mg) · LDN children with Crohn's disease (Cochrane review) PMID 29607497

Further reading: detailed protocols

• LDN Research Trust: prescriber and research guides ldnresearchtrust.org

10Connections

11Sources

1. PMID 17222320 — Smith JP et al. Am J Gastroenterol 2007;102(4):820–828 — open-label pilot in active Crohn's (n=17), 67% remissionPubMed 17222320
2. PMID 21380937 — Smith JP et al. Dig Dis Sci 2011;56(7):2088–2097 — RCT, naltrexone 4.5 mg in active Crohn's, mucosal healing demonstratedPubMed 21380937
3. DOI 10.1007/s10620-011-1653-7DOI 10.1007/s10620-011-1653-7
4. NCT00663117 — Penn State Crohn's RCT registry entryNCT00663117

12Entry history

Heretic informs and never prescribes. Where amounts appear, they describe what published studies used. Talk to a qualified clinician before acting on anything here.