The evolution of Low-Dose Naltrexone: A comprehensive timeline from opioid antagonist to potential game-changer in chronic autoimmune conditions

Low dose naltrexone (LDN) is a prominent example of drug repurposing in which a well?characterised opioid receptor antagonist, originally developed for substance use disorders, has been investigated at substantially lower doses for potential immunomodulatory and anti inflammatory effects. This review summarises the chronological development of LDN research, highlighting key mechanistic frameworks and influential research groups—from early observations of dose?dependent biological divergence to later work implicating the OGF–OGFr axis, microglial modulation, and innate immune signalling pathways (including TLR4 related hypotheses).

Five key takeaways

• Translation remains constrained by evidence quality and heterogeneity-Despite mechanistic sophistication and encouraging preclinical/observational findings, the clinical evidence base remains limited by small sample sizes, variable endpoints, and incomplete replication across indications; consequently, the relative contribution of each proposed mechanism likely varies by condition and requires further rigorous clinical evaluation.
• LDN represents a dose-dependent pharmacological paradigm shift-The LDN literature consistently emphasises that low-dose administration may produce qualitatively different biological effects compared with standard-dose naltrexone, supporting the broader concept that exposure pattern and blockade duration can alter downstream signalling.
• The OGF–OGFr axis provides a mechanistic scaffold linking endogenous opioids to immune regulation-Work by Zagon and McLaughlin substantially advanced the field by characterising the OGF–OGFr pathway and demonstrating that intermittent blockade can modulate enkephalin dynamics, with downstream relevance to immune function and experimental autoimmune models.
• Neuroimmune mechanisms broadened the explanatory model beyond classical opioid receptor pharmacology-The “glial modulation” hypothesis (including microglial activation states and immunometabolic shifts) reframed LDN as a candidate neuroimmune modulator, offering a plausible mechanistic bridge to symptom domains such as pain, fatigue, and central sensitisation.
• Innate immune signalling (including TLR4-related pathways) emerged as a plausible opioid-independent mechanism-The integration of TLR4 into the LDN discussion—often associated with glial/innate immune work—supported the hypothesis that some observed anti-inflammatory effects may not be fully explained by opioid receptor antagonism alone.

Introduction

Low-dose naltrexone (LDN) represents a remarkable example of drug repurposing, transforming from a high-dose opioid antagonist for addiction treatment into a promising immunomodulatory agent for chronic autoimmune diseases. This literature review presents a comprehensive timeline of low dose naltrexone’s development, highlighting key discoveries, leading researchers, and mechanistic breakthroughs that have shaped our understanding of LDN’s therapeutic potential. From Bernard Bihari’s pioneering observations in 1985 to the recent discovery of stereoselective TLR4 antagonism, the journey of LDN exemplifies how persistent scientific inquiry can reveal unexpected therapeutic applications [1].

The Foundation Era (1963-1985): From opioid blockade to immunomodulation

Initial development as an opioid antagonist

Naltrexone was first synthesised in 1963 as an opioid receptor antagonist, designed to block the effects of morphine and heroin without activating opioid receptors [1]. The compound underwent extensive development and clinical testing throughout the 1970s, with particular focus on its application in treating opioid and alcohol dependence. The Food and Drug Administration (FDA) approved naltrexone in 1984 for opioid use disorder at a standard dose of 50 mg per day, marking the culmination of over two decades of development [2]. This approval established naltrexone’s role in addiction medicine, though its true potential remained unexplored.

Bernard Bihari’s paradigm-shifting discovery

The trajectory of naltrexone research changed dramatically in 1985 when Dr Bernard Bihari made a groundbreaking observation that would reshape the field. Bihari discovered that when naltrexone is administered in very low doses (1-5 mg/day) before bedtime, it produces effects entirely different from its standard high-dose application [1]. His key insight was that low-dose administration results in transient opioid receptor blockade lasting only 2-4 hours, which triggers a compensatory upregulation of endogenous opioid production. This rebound effect leads to increased endorphin secretion in the early morning hours, serving as an indirect opioid agonist and immunomodulatory agent [1]. Bihari’s initial work focused on AIDS patients, where he demonstrated that this extra endorphin secretion could enhance immune system response [1].

The importance of Bihari’s discovery cannot be overstated—it established the fundamental principle of intermittent receptor blockade, which was later elaborated upon by subsequent researchers. His work revealed that the duration and completeness of receptor blockade were critical determinants of biological response, a concept that would become central to understanding LDN’s mechanisms of action [3].

Figure 1. Comprehensive timeline of low-dose naltrexone development from 1963 to 2025. The timeline illustrates major discoveries, regulatory milestones, mechanistic insights, and clinical applications across four distinct eras. Bubble size represents the relative importance of each discovery.

The OGF-OGFr Era (1990-2010): Molecular mechanisms unveiled

Zagon and McLaughlin’s pioneering work

The period from 1990 to 2010 witnessed the systematic elucidation of the molecular mechanisms underlying LDN’s effects, primarily through the work of Ian Zagon and Patricia McLaughlin at Pennsylvania State University. Their research program, spanning nearly three decades, identified and characterised the opioid growth factor (OGF)-OGF receptor (OGFr) axis, providing a molecular framework for understanding how endogenous opioids regulate cell proliferation and immune function [4].

Zagon and McLaughlin demonstrated that OGF, chemically identified as met-enkephalin, functions as an inhibitory growth factor that maintains homeostatic cell replication [5]. When bound to its specific receptor, OGFr, located on the outer nuclear envelope, OGF upregulates cyclin-dependent inhibitory kinases p16 and p21, thereby slowing cell replication through G1/S phase delay [5]. This mechanism proved fundamental to understanding not only cancer biology but also immune regulation.

The intermittent blockade paradigm

A critical insight from Zagon and McLaughlin’s work was the recognition that the duration and completeness of OGFr blockade determines the biological outcome. They established that intermittent blockade of the OGF-OGFr pathway with low doses of naltrexone results in a biofeedback mechanism that upregulates serum enkephalin levels. In contrast, complete blockade produces the opposite effect—accelerated cell proliferation [5]. This elegant demonstration explained Bihari’s earlier observations and provided a mechanistic rationale for the specific dosing requirements of LDN therapy.

In their studies of experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis, Zagon and McLaughlin showed that immunisation alone resulted in reduced enkephalin levels [5]. Critically, therapy with LDN restored serum enkephalin levels in EAE mice, resulting in improved behavioural scores and diminished central nervous system (CNS) pathology [5]. These preclinical findings provided the first direct evidence that LDN could modulate autoimmune disease processes through the OGF-OGFr axis.

Clinical translation and early MS studies

The work of Zagon and McLaughlin extended beyond mechanistic studies to clinical observations. Their research demonstrated that serum enkephalin levels were decreased in patients with multiple sclerosis relative to subjects with other neurological disorders [5]. Clinical studies reported that low-dose naltrexone was beneficial in enhancing quality of life, reducing fatigue, and increasing motor activity in humans with fibromyalgia, Crohn’s disease, and multiple sclerosis, with treatment well tolerated even after several years of therapy [5]. Long-term observational studies showed that patients with relapsing-remitting MS maintained stable health over 10-year periods when treated with LDN, either alone or as adjunct therapy [6].

The Stanford/Younger Revolution (2010-2015): Glial modulation paradigm

A new perspective on neuroinflammation

The period from 2010 to 2015 witnessed a paradigm shift in understanding LDN’s mechanisms of action, driven primarily by the work of Jarred Younger and colleagues at Stanford University. Younger’s group proposed that low-dose naltrexone acts as a novel anti-inflammatory agent in the central nervous system via direct action on microglial cells, effects that appear entirely independent of naltrexone’s better-known activity at classical opioid receptors [7]. This represented a fundamental reconceptualisation of LDN’s therapeutic potential, shifting focus from compensatory opioid upregulation to direct modulation of neuroinflammatory processes.

Younger and colleagues demonstrated that LDN has been shown to reduce symptom severity in conditions such as fibromyalgia, Crohn’s disease, multiple sclerosis, and complex regional pain syndrome [7]. Their research suggested that at doses of 1-5 mg, LDN acts as a glial modulator with neuroprotective effects by inhibiting microglial activation [3]. This dual mechanism—transient opioid receptor blockade combined with microglial modulation—provided a more comprehensive explanation for LDN’s broad therapeutic effects across diverse conditions.

Clinical evidence and mechanistic insights

The Stanford group’s work was particularly important in establishing LDN as potentially “one of the first glial cell modulators to be used for the management of chronic pain disorders” [7]. Their clinical trials in fibromyalgia patients demonstrated significant reductions in pain severity and fatigue, supporting the glial modulation hypothesis. However, Younger and colleagues appropriately noted that despite the initial promise of efficacy, the use of LDN for chronic disorders remained highly experimental, with published trials having low sample sizes and few replications [7].

Recent studies have further elaborated on these mechanisms, showing that LDN induces a shift from a highly activated pro-inflammatory phenotype (iNOS^high^CD206^low^) to a quiescent anti-inflammatory M2 phenotype (iNOS^low^CD206^high^) in microglial cells [8]. Changes in the inflammatory profile are accompanied by cellular metabolic switching, transitioning from high glycolysis to mitochondrial oxidative phosphorylation (OXPHOS), with LDN-treated cells able to maintain a metabolically suppressive phenotype that supports OXPHOS and high oxygen consumption [8].

Figure 2. Key mechanistic discoveries and clinical research applications over time. The left panel shows the relative importance of the four significant mechanistic insights. The right panel displays the progression of clinical research across different disease conditions from 2000-2025.

The TLR4 Discovery and Integration Era (2015-2025): Stereochemistry and molecular targeting

Discovery of TLR4 antagonism

From around 2015 onwards, a key strand of LDN research began to explain some of its anti-inflammatory effects without relying on classical opioid receptor blockade. This shift was driven largely by the “glial/TLR4” line of work, most closely associated with Hutchinson and colleagues, who helped bring TLR4 (and the TLR4/MD2 complex) into the conversation as a plausible non-opioid pathway relevant to pain and neuroinflammation.

Building on that foundation, Xiaohui Wang and colleagues provided a more chemistry-led piece of the puzzle by showing that naltrexone’s interaction with Toll-like receptor 4 (TLR4) appears to be highly stereoselective [9]. Their work revealed that (+)-naltrexone, the dextrorotatory stereoisomer, exhibits TLR4 antagonistic activity 100 times stronger than the standard racemic mixture, while not interacting with classical opioid receptors [9].

Why was stereoselectivity a breakthrough?

This stereochemistry angle was important because it supported the idea that “LDN effects” might not be explained purely by opioid receptor pharmacology. Wang’s group reported that (+)-naltrexone (and related precursors) demonstrated TLR4 antagonistic activity with signalling effects consistent with targeting the TLR4–TRIF pathway [9]. In vivo, these compounds reduced several morphine associated behavioural effects (such as sensitisation and conditioned place preference), alongside markers consistent with reduced microglial activation and lower TNF alpha expression in brain regions including the medial prefrontal cortex and ventral tegmental area [9].

Molecular optimisation and enhanced potency

Building on these findings, recent research has focused on optimising the TLR4 antagonistic properties of naltrexone derivatives. In 2024, Wang’s group reported the development of CIAC101, an isobutyl-substituted (+)-naltrexone derivative with nanomolar TLR4 antagonism, representing a remarkable 6,200-fold higher potency than (+)-naltrexone [10]. CIAC101 dose-dependently blocked lipopolysaccharide-induced NF-kB activation and reduced the expression of pro-inflammatory mediators in microglia [10]. Low-dose CIAC101 (0.2 mg/kg) attenuated methamphetamine-induced behavioural sensitisation and conditioned place preference without intrinsic rewarding effects, mechanistically reducing microglial activation and inflammatory gene expression within addiction-relevant circuits [10].

The stereochemistry research also revealed that (+)-norbinaltorphimine, formed by linking two naltrexone units through a rigid pyrrole spacer, showed 25 times better TLR4 antagonist activity than naltrexone in microglial cells, whereas (-)-norbinaltorphimine lost TLR4 activity [11]. This enantioselectivity, confirmed in primary microglia, astrocytes, and macrophages, provided the first report showing enantioselective modulation of innate immune TLR signalling [11].

Integration of multiple mechanisms

Contemporary understanding recognises that LDN’s therapeutic effects result from the integration of multiple mechanistic pathways working synergistically. Low-dose naltrexone acts through at least four distinct but interconnected mechanisms: (1) compensatory upregulation of endogenous opioids through transient receptor blockade, (2) modulation of the OGF-OGFr axis affecting cell proliferation and immune regulation, (3) direct anti-inflammatory effects through glial cell modulation, and (4) TLR4 antagonism reducing pro-inflammatory cytokine production [3]. This mechanistic diversity explains LDN’s broad therapeutic potential across seemingly disparate conditions.

Clinical translation: EAE/MS and broader autoimmune applications

Preclinical evidence in autoimmune models

The experimental autoimmune encephalomyelitis (EAE) model has proven particularly valuable for understanding LDN’s effects in autoimmune diseases. Recent comprehensive studies by Zagon, McLaughlin, and colleagues demonstrated that both prophylactic and therapeutic administration of LDN significantly ameliorated EAE pathology [12]. Prophylactically treated EAE mice receiving either OGF or LDN had markedly reduced spinal cord inflammation (OGF: p=0.03; LDN: p<0.01) and white matter blood vessel density (OGF: p<0.0001; LDN: p<0.0001) compared to vehicle-treated EAE mice [12].

Therapeutic administration also proved effective, with EAE mice receiving OGF or LDN showing improved clinical behaviour and reduced white matter blood vessel density after 3 weeks of treatment [12]. These studies provided the first demonstration of a role for LDN and the OGF-OGFr axis in reducing angiogenesis in EAE mice, a novel mechanism relevant to MS pathophysiology [12]. The timing of treatment initiation proved critical, with prophylactic treatment delaying disease onset and suppressing neutrophil replication and lymphocyte proliferation, while traditional therapy initiated at disease presentation reversed behavioural deficits and restored OGF and IL-17 serum levels within 8 days [13].

Reduced serum OGF levels in untreated EAE mice correlated with increased microglia activation within lumbar spinal cords. However, both OGF and LDN reduced microglial activation, but only prophylactic treatment stopped CNS macrophages from clustering. Overall, the findings suggest that when OGF or LDN is started changes the outcome: earlier treatment can help prevent, and later treatment can help reverse, behavioural deficits, inflammatory cytokine activity, and spinal cord pathology [13].

Peripheral immune modulation

An important mechanistic insight from EAE studies was LDN’s effect on peripheral immune cell populations. Endogenous opioid inhibition of T and B cell subpopulation proliferation in response to immunisation was demonstrated through flow cytometry studies [14]. Exogenous OGF or endogenous OGF following LDN suppressed T and B lymphocyte proliferation in the spleen and inguinal lymph nodes of myelin oligodendrocyte glycoprotein (MOG)-immunised mice [14]. Suppression of peripheral immune cell CD4+ and CD8+ T cell proliferation at 5 and 12 days correlated with reductions in clinical behaviour, providing novel mechanistic pathways underlying the efficacy of OGF and LDN therapy for MS [14].

Clinical evidence and registry studies

Clinical evidence for LDN’s efficacy in autoimmune diseases has accumulated through observational studies and registry analyses. A particularly important contribution came from a Norwegian nationwide register-based controlled quasi-experimental before-and-after study examining LDN use in rheumatoid and seropositive arthritis [15]. In persistent LDN users, there was a 13% relative reduction in cumulative defined daily doses (DDD) of all medicines examined, corresponding to -73.3 DDD per patient (95% CI -120.2 to -26.4, p = 0.003), and a 23% reduction of analgesics (-21.6 DDD, 95% CI -35.5 to -7.6, p<0.009) [15]. Persistent LDN users had significantly reduced DDDs of NSAIDs and opioids, and a lower proportion of users of disease-modifying antirheumatic drugs (DMARDs), TNF-alpha antagonists, and opioids [15].

Clinical observations in MS patients treated with LDN over long-term follow-up (150 months post-diagnosis) showed that the therapy appeared non-toxic and inexpensive, with no significant differences in clinical laboratory values, timed walking tests, or changes in MRI between LDN-treated patients and those on conventional disease-modifying therapies [6]. These data suggested that LDN, if taken alone, did not result in exacerbation of disease symptoms and maintained stable health in patients with relapsing-remitting multiple sclerosis [6].

Figure 3. Key researchers and their contributions to LDN development. The network illustrates the chronological progression of major contributors and their impact across various clinical application areas, showing how discoveries have built on one another over time.

Integrative mechanisms: Multiple pathways converge

The Compensatory Upregulation Pathway

The compensatory upregulation mechanism, first described by Bihari, remains a cornerstone of LDN’s therapeutic effects. At low doses (1-5 mg), LDN transiently blocks opioid receptors, enhancing endorphin release through a rebound effect [16]. This transient blockade upregulates opioid signalling, resulting in increased levels of endogenous opioid production—the so-called opioid rebound effect [3]. The increased production and sensitivity of OGF, met-enkephalin (ME), and OGF receptor (OGFr) in the bloodstream enhance quality of life and contribute to immunomodulatory effects [1].

The OGF-OGFr regulatory axis

The OGF-OGFr axis functions as a tonically active negative regulator in neoplasia and immune regulation. OGF is an inhibitory growth factor that upregulates p16 and/or p21 cyclin-dependent inhibitory kinases to slow cell replication [5]. Intermittent blockade of the OGF-OGFr pathway with LDN triggers a biofeedback mechanism that upregulates serum enkephalin levels, whereas complete blockade accelerates cell proliferation and growth [5]. This mechanism explains why dose and timing are critical for therapeutic efficacy—the goal is intermittent, not complete, receptor blockade.

Glial and microglial modulation

LDN’s effects on glial cells represent a distinct mechanism involving direct cellular reprogramming. By modulating phenotypic features through metabolic switching of activated microglia, naltrexone was found to be an effective and powerful tool for immunometabolic reprogramming [8]. In a dose-dependent manner, naltrexone modulated mTOR/S6K expression, which underlies the regulation of cell metabolic phenotype, microglial immune properties, and adaptation [8]. The metabolic shift induced by the transition from glycolysis to mitochondrial oxidative metabolism was more prominent in cells pretreated with immunometabolic modulators such as lipopolysaccharide (LPS) and interferon-gamma [8].

TLR4-mediated anti-inflammatory effects

The TLR4 antagonism mechanism operates independently of classical opioid receptors and targets innate immune signalling. LDN binds to Toll-like receptor 4 and acts as an antagonist, inhibiting downstream cellular signalling pathways that ultimately lead to the production of pro-inflammatory cytokines, thereby reducing the inflammatory response [3]. Naltrexone inhibited production of IL-6 and TNF-alpha in monocyte and plasmacytoid dendritic cell subsets within peripheral blood mononuclear cell populations after treatment with TLR7/8 and TLR9 ligands, respectively [17]. These findings indicate that LDN can modulate cytokine responses to TLR signalling, supporting the hypothesis that it may have immunomodulatory effects [17].

Comparative importance of discoveries and researchers

Foundational contributions

Bernard Bihari (1985) deserves recognition as the pioneer who initiated the LDN field through his observation of compensatory upregulation. His work established the fundamental principle that low-dose administration produces qualitatively different effects than high-dose administration, setting the stage for all subsequent research. Importance rating: 9/10 (foundational but mechanistically incomplete).

Ian Zagon and Patricia McLaughlin (1990-2025) made the most sustained and comprehensive contributions to the field, spanning over three decades. Their identification and characterisation of the OGF-OGFr axis provided the first molecular framework for understanding LDN’s effects. Their extensive preclinical work in EAE models demonstrated clear therapeutic efficacy and elucidated peripheral immune mechanisms. Their work bridged basic science and clinical application, making them arguably the most important contributors to the field. Importance rating: 10/10 (comprehensive mechanistic understanding and clinical translation).

Paradigm-shifting insights

Jarred Younger and Stanford colleagues (2014) revolutionised the field by identifying LDN as a glial cell modulator, shifting the focus from purely opioid-mediated mechanisms to direct anti-inflammatory effects on microglia. This work opened new avenues for understanding chronic pain and neuroinflammatory conditions and positioned LDN as a potential first-in-class glial modulator. Importance rating: 9.5/10 (paradigm shift with broad implications).

Xiaohui Wang and colleagues (2019-2024) made breakthrough discoveries regarding stereochemistry and TLR4 binding, revealing an entirely new mechanism independent of opioid receptors. Their development of dramatically more potent derivatives (CIAC101 with 6,200-fold greater potency) represents a potential leap forward in therapeutic applications. This work explains many previously poorly understood anti-inflammatory effects. Importance rating: 10/10 (novel mechanism with translational potential).

Tables: Key studies and mechanisms    

Table 1: Major clinical studies of LDN in autoimmune diseases

Study	Year	Disease	Design	N	Dose	Duration	Key Findings	Citation
Ludwig et al.	2016	RRMS	Retrospective	23	4.5 mg/day	10 years	Stable disease, no exacerbations, safe profile	[6]
Raknes & Smbrekke	2019	RA	Registry	360	1-5 mg/day	1 year	13% reduction in total medication use, 23% reduction in analgesics	[15]
Zagon et al.	2018	MS/EAE	Clinical review	Multiple	0.1-10 mg/kg	Variable	Reduced fatigue, improved QOL, restored enkephalin levels	[5]
Patel et al.	2021	EAE	Preclinical	Mouse	0.1 mg/kg	8 days	Reversed behavioural deficits, reduced microglial activation	[13]
Odom et al.	2025	EAE	Preclinical	Mouse	0.1 mg/kg	3 weeks	Reduced angiogenesis, decreased inflammation	[12]

Table 2: Mechanistic pathways of Low-Dose Naltrexone

Mechanism	Key Mediators	Timeline of Discovery	Discoverers	Primary Effects	Citation
Compensatory Upregulation	Endorphins, Enkephalins	1985	Bihari	? Endogenous opioid production, enhanced immune function	[1]
OGF-OGFr Axis	Met-enkephalin, OGFr, p16/p21	1990-2010	Zagon & McLaughlin	Cell cycle regulation, Immune modulation, ? Proliferation	[5]
Glial Modulation	Microglia, M1/M2 polarization	2014	Younger et al.	? Neuroinflammation, Metabolic switching, ? Pro-inflammatory cytokines	[7]
TLR4 Antagonism	TLR4-TRIF pathway, NF-?B	2019-2024	Wang et al.	? TNF-alpha ? IL-6, ? Microglial activation (opioid-independent)	[9]

Table 3: Evolution of LDN potency through molecular optimisation

Compound	Year	Relative TLR4 Potency	Key Features	Discoverers	Citation
Naltrexone (racemic)	1963-1984	1x (baseline)	Non-selective opioid antagonist	Original synthesis	[1]
(+)-Naltrexone	2019	100x	Stereoselective TLR4 antagonist, no opioid binding	Zhang et al., Wang et al.	[9]
(+)-14-hydroxycodeinone	2024	100x	TLR4-TRIF pathway selective	Gao et al.	[9]
(+)-Norbinaltorphimine	2019	25x	Bivalent ligand, enantioselective	Zhang et al.	[11]
CIAC101	2024	6,200x	Nanomolar TLR4 antagonism, isobutyl-substituted	Gao et al.	[10]

Current understanding and future directions

Dosing strategies and patient selection

Current evidence suggests optimal LDN dosing ranges from 1-5 mg daily, typically administered at bedtime to capitalise on circadian rhythms of endogenous opioid production [1]. However, dosing may need to be individualised based on specific conditions—registry data suggest that persistent users at these doses show the most significant benefit [15]. Patient selection criteria remain under investigation, though conditions characterised by elevated inflammatory markers and immune dysregulation appear most responsive. Patients with neuropathic pain or complex regional pain syndrome showed significantly greater likelihood of pain relief from LDN compared to those with spondylosis, suggesting disease-specific responses [18].

Combination therapies and adjunct use

LDN’s favourable safety profile and multiple mechanisms of action make it attractive for combination strategies. Long-term MS studies showed LDN could be safely used as adjunct therapy to conventional disease-modifying treatments without adverse interactions [6]. The Norwegian registry data demonstrated that LDN use was associated with reduced need for conventional medications, including analgesics, NSAIDs, and disease-modifying antirheumatic drugs [15]. Future studies should systematically evaluate optimal combinations and whether LDN can reduce reliance on more toxic immunosuppressive agents.

Next-generation TLR4 antagonists

The development of CIAC101 with 6,200-fold greater TLR4 antagonism than (+)-naltrexone opens exciting possibilities for more potent anti-inflammatory therapies [10]. Low-dose CIAC101 (0.2 mg/kg) attenuated behavioural sensitisation and conditioned place preference in addiction models, demonstrating robust antineuroinflammatory activity [10]. These findings advance a neuroimmune strategy that could extend beyond addiction to autoimmune diseases. Further optimisation of (+)-naltrexone derivatives targeting specific inflammatory pathways may yield therapeutics with enhanced efficacy and specificity.

Unanswered questions and research needs

Despite substantial progress, several critical questions remain. Large-scale, well-designed randomised controlled trials with adequate sample sizes and duration are still lacking for most autoimmune conditions [7]. The relationship between B-cell repopulation dynamics, peripheral immune responses, and central nervous system effects requires clarification. Biomarkers predicting LDN response would facilitate patient selection and personalised dosing. The relative contributions of each mechanistic pathway to therapeutic effects across different diseases remain incompletely understood. Finally, long-term safety data beyond 10 years are needed to fully establish LDN’s risk-benefit profile for chronic use.

Conclusion

The journey of low-dose naltrexone from a high-dose opioid antagonist to a potential game-changer in chronic autoimmune conditions represents a remarkable example of scientific discovery building upon serendipitous observation. Bernard Bihari’s 1985 insight into compensatory upregulation initiated this journey, but the systematic mechanistic work of Zagon and McLaughlin over three decades provided the molecular foundation that explained and expanded upon Bihari’s observations. Jarred Younger’s recognition of glial modulation shifted the paradigm toward understanding LDN’s direct anti-inflammatory effects, while recent work by Wang and colleagues on TLR4 stereochemistry has revealed entirely new therapeutic mechanisms.

Each major discovery has weighted importance in the overall development of LDN therapeutics. Zagon and McLaughlin’s OGF-OGFr axis work (10/10 importance) provided the most comprehensive mechanistic framework and bridged preclinical to clinical research. Wang’s TLR4 discoveries (10/10 importance) opened new avenues for dramatically enhanced potency through molecular optimisation. Younger’s glial modulation paradigm (9.5/10 importance) reconceptualised LDN as a neuroinflammatory modulator with broad applications. Bihari’s initial observation (9/10 importance), although mechanistically incomplete, was foundational and launched the field.

Looking forward, the convergence of multiple mechanistic pathways—compensatory upregulation, OGF-OGFr modulation, glial reprogramming, and TLR4 antagonism—explains LDN’s broad therapeutic potential while highlighting opportunities for optimisation. The development of ultra-potent derivatives like CIAC101 suggests that the best applications of this therapeutic approach may still lie ahead. However, realising this potential requires well-designed clinical trials, identification of predictive biomarkers, and systematic evaluation of combination strategies. The LDN story exemplifies how persistent investigation of unexpected observations can yield transformative therapeutic insights, offering hope to millions of patients with chronic autoimmune conditions who currently lack effective, well-tolerated treatments.

This information is for general guidance only. For medical advice, please consult your doctor or healthcare provider.

References:

[1] Courier Pharmacy. (2025). How does LDN work? [online] Available at: https://courierpharmacy.co.uk/how-does-ldn-work/ [Accessed 10 Nov. 2025].

[2] R. Meyer, “Pharmacotherapy of Substance Use Disorders: Challenges and Opportunities.,” Journal of Clinical Psychopharmacology, Jul. 2020, doi: 10.1097/JCP.0000000000001218.

[3] D. Trofimovitch and S. J. Baumrucker, “Pharmacology Update: Low-Dose Naltrexone as a Possible Nonopioid Modality for Some Chronic, Nonmalignant Pain Syndromes,” The American journal of hospice & palliative care, Mar. 2019, doi: 10.1177/1049909119838974.

[4] I. Zagon and P. McLaughlin, “Biology of the Opioid Growth Factor  Opioid Growth Factor Receptor Axis: Bench to Bedside and Back,” Medical Research Archives, 2024, doi: 10.18103/mra.v12i6.5369.

[5] I. Zagon and P. McLaughlin, “Intermittent blockade of OGFr and treatment of autoimmune disorders,” Experimental biology and medicine, Dec. 2018, doi: 10.1177/1535370218817746.

[6] M. D. Ludwig, A. Turel, I. Zagon, and P. McLaughlin, “Long-term treatment with low dose naltrexone maintains stable health in patients with multiple sclerosis,” Multiple sclerosis journal – experimental, translational and clinical, Sep. 2016, doi: 10.1177/2055217316672242.

[7] J. Younger, L. Parkitny, and D. Mclain, “The use of low-dose naltrexone (LDN) as a novel anti-inflammatory treatment for chronic pain,” Clinical Rheumatology, Feb. 2014, doi: 10.1007/s10067-014-2517-2.

[8] N. Kui, V. Raki, R. Verko, T. Vidovic, I. Grahovac, and J. Mri-Peli, “Immunometabolic Modulatory Role of Naltrexone in BV-2 Microglia Cells,” International Journal of Molecular Sciences, Aug. 2021, doi: 10.3390/ijms22168429.

[9] J. Gao et al., “Exploring the Function of (+)-Naltrexone Precursors: Their Activity as TLR4 Antagonists and Potential in Treating Morphine Addiction.,” Journal of Medicinal Chemistry, Feb. 2024, doi: 10.1021/acs.jmedchem.3c02316.

[10] J. Gao, C. Lin, L. Deng, H. Wang, and X. Wang, “Nanomolar TLR4 Antagonist CIAC101 Derived from (+)-Naltrexone Blocks Microglial Activation and Methamphetamine Addiction.,” Journal of Medicinal Chemistry, Nov. 2025, doi: 10.1021/acs.jmedchem.5c02596.

[11] X. Zhang et al., “Stereochemistry and innate immune recognition: (+)norbinaltorphimine targets myeloid differentiation protein 2 and inhibits tolllike receptor 4 signaling,” The FASEB Journal, Jun. 2019, doi: 10.1096/fj.201900173RRR.

[12] L. Odom, I. Zagon, and P. McLaughlin, “Prophylactic and Therapeutic Modulation of the OGF-OGFr Axis Ameliorates Angiogenesis-associated Pathology in Experimental Autoimmune Encephalomyelitis,” Journal of experimental neurology, 2025, doi: 10.33696/neurol.6.110.

[13] C. Patel, I. Zagon, M. Pearce-Clawson, and P. McLaughlin, “Timing of treatment with an endogenous opioid alters immune response and spinal cord pathology in female mice with experimental autoimmune encephalomyelitis,” Journal of Neuroscience Research, Nov. 2021, doi: 10.1002/jnr.24983.

[14] P. McLaughlin, D. McHugh, M. J. Magister, and I. Zagon, “Endogenous opioid inhibition of proliferation of T and B cell subpopulations in response to immunization for experimental autoimmune encephalomyelitis,” BMC Immunology, Apr. 2015, doi: 10.1186/s12865-015-0093-0.

[15] G. Raknes and L. Smbrekke, “Low dose naltrexone: Effects on medication in rheumatoid and seropositive arthritis. A nationwide register-based controlled quasi-experimental before-after study,” PLoS ONE, Feb. 2019, doi: 10.1371/journal.pone.0212460.

[16] W. Pietruszka et al., “Pain Relief Without Opioids? Revisiting Naltrexone in Low Doses for Chronic Pain,” Quality in Sport, May 2025, doi: 10.12775/qs.2025.41.59792.

[17] R. Cant, A. Dalgleish, and R. Allen, “Naltrexone Inhibits IL-6 and TNF Production in Human Immune Cell Subsets following Stimulation with Ligands for Intracellular Toll-Like Receptors,” Frontiers Media, Jul. 2017, doi: https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2017.00809/full

[18] A. McKenzie-Brown, D. Boorman, K. R. Ibanez, E. Agwu, and V. Singh, “Low-Dose Naltrexone (LDN) for Chronic Pain at a Single Institution: A Case Series,” Journal of Pain Research, Jun. 2023, doi: 10.2147/JPR.S389957.