Naltrexone
Also known as: LDN, Low-Dose Naltrexone, ReVia, Vivitrol
Opioid Antagonist | Low-Dose Anti-Inflammatory & Immune Modulation
Overview
Naltrexone is an opioid receptor antagonist originally developed and FDA-approved at full dose (50 mg) for the treatment of opioid and alcohol use disorders. At this dose, it competitively blocks mu-opioid receptors, preventing the euphoric and reinforcing effects of opioids and reducing alcohol cravings. However, naltrexone has gained enormous popularity in the biohacking and functional medicine communities at dramatically lower doses (1-4.5 mg), commonly referred to as Low-Dose Naltrexone (LDN). At these sub-therapeutic doses, naltrexone produces a brief, transient blockade of opioid receptors lasting only a few hours, which triggers a compensatory upregulation of endogenous endorphins and enkephalins. This rebound effect, combined with direct modulation of the Opioid Growth Factor (OGF) - OGF receptor axis, produces broad anti-inflammatory and immunomodulatory effects that have shown promise across a wide range of autoimmune, inflammatory, and chronic pain conditions.
Key benefits
- Broad anti-inflammatory and immunomodulatory effects via OGF-OGFr axis upregulation
- Reduction in pro-inflammatory cytokines (TNF-alpha, IL-6, IL-12) through TLR4 antagonism
- Compensatory upregulation of endogenous endorphins and enkephalins (200-300% increase)
- Improved immune regulation and rebalancing of Th1/Th2/Th17 responses
- Reduction in chronic pain through central and peripheral opioid system modulation
- Potential improvement in mood, anhedonia, and overall well-being via endorphin enhancement
- Extremely well-tolerated with minimal side effects at low doses
- Low cost, especially as compounded LDN formulation
Mechanism of action
At low doses (1-4.5 mg), naltrexone produces a brief nocturnal blockade of opioid receptors that lasts approximately 4-6 hours. This transient blockade triggers a compensatory upregulation of endogenous opioid production, including beta-endorphin and met-enkephalin (also known as Opioid Growth Factor, OGF). Elevated OGF interacts with the OGF receptor (OGFr) to modulate cell proliferation and immune function. LDN also directly antagonizes Toll-like receptor 4 (TLR4) on microglia and macrophages, reducing neuroinflammation and systemic inflammatory cytokine production including TNF-alpha, IL-6, and IL-12. The net effect is a shift from a pro-inflammatory Th1/Th17-dominant immune profile toward a more balanced regulatory state. Additionally, LDN has been shown to increase circulating endorphin levels by 200-300%, which contributes to improved mood, reduced pain perception, and enhanced immune surveillance. The bedtime dosing strategy is deliberate: the brief receptor blockade occurs during the natural nocturnal endorphin surge, maximizing the compensatory rebound effect.
Molecular data
- Type
- Opioid antagonist (C20H23NO4)
- Half-life
- ~4 hours
Indications
What the research community uses this compound for, with self-reported effectiveness.
Autoimmune & Inflammatory
Chronic Pain & Fatigue
Mental Health & Neurological
Dosing protocols
Common protocols by delivery method. Adjust the curve below to model accumulation in your own cycle.
Delivery method
| Protocol | Dose | Frequency | Duration |
|---|---|---|---|
| — | 1.5 mg, titrate to 4.5 mg | Once daily at bedtime | — |
| — | 0.5-1.0 mg, titrate slowly to 4.5 mg | Once daily at bedtime | — |
| — | 50 mg/day | Once daily | — |
| — | 50 mg/day | Once daily | — |
Safety
Reported adverse effects, contraindications, and what to monitor on cycle.
Common side effects
- Vivid dreams or unusually intense dreaming - the most frequently reported side effect, typically diminishes over 1-2 weeks
- Initial sleep disruption or insomnia during the first week of treatment
- Mild nausea, particularly during the first few days
- Transient headache during dose initiation or titration
Rare side effects
- Temporary worsening of autoimmune symptoms (immune rebalancing flare) during the first 1-2 weeks
- Anxiety or irritability during initial titration
- Mild hair thinning (reported anecdotally, typically reversible with dose adjustment)
- Hepatotoxicity (only documented at full 50 mg dose in rare cases, not reported with LDN dosing)
Contraindications
- Current use of opioid medications or active opioid dependence (must be opioid-free 7-10 days minimum)
- Acute hepatitis or severe hepatic impairment (primarily relevant at full dose)
- Known hypersensitivity to naltrexone
- Anticipated need for opioid pain medication (e.g., upcoming surgery - discontinue LDN 3-7 days prior)
Monitoring
- Liver function tests (AST/ALT): at baseline; periodic monitoring primarily recommended for full-dose (50 mg) use
- Symptom tracking: maintain a log of pain levels, energy, mood, and sleep quality to assess response
- Autoimmune markers (if applicable): CRP, ESR, and disease-specific antibodies at baseline and every 3-6 months
- Thyroid function: in Hashimoto's patients, monitor TSH and free T4 as LDN may improve thyroid function, potentially requiring dose reduction of thyroid medication
References
Primary literature and clinical-trial data informing this entry.