Dihexa for ME/CFS (Myalgic Encephalomyelitis / Chronic Fatigue Syndrome): DecodeME, BDNF, Microglial Neuroinflammation, LDN & the 2026 UK Review

Around 250,000 UK adults and children live with Myalgic Encephalomyelitis / Chronic Fatigue Syndrome (ME/CFS) on combined Action for ME and ME Association figures, with women representing 75–85% of cases and roughly 25% of patients housebound or bedbound. The 2025–2026 window has been the most consequential in decades: on 6 August 2025 the DecodeME genome-wide association study preprint reported eight genome-wide significant loci across 15,579 European-ancestry ME/CFS cases, with lead genes (RABGAP1L, BTN2A2, OLFM4, FBXL4, CA10) implicating viral-defence, immune and mitochondrial biology and a striking female-only sex-specific signal; on 22 July 2025 the UK Department of Health and Social Care published My Full Reality - the final UK ME/CFS Delivery Plan; in April 2025 the ME Association funded the UBC low-dose naltrexone trial in post-COVID fatigue syndrome and ME/CFS led by Dr Luis Nacul; in October 2024 Assistant Coroner Deborah Archer issued the Maeve Boothby O’Neill Prevention of Future Deaths report; and the February 2024 NIH Walitt deep-phenotyping Nature Communications paper reframed post-infectious ME/CFS as a central rather than peripheral disorder. Within this picture, Dihexa — a synaptogenic peptide that activates the HGF/c-Met growth-factor system — is mechanistically interesting for the cognitive and neuroinflammatory components of ME/CFS, but is also potentially risky given the post-exertional malaise (PEM) directionality concern. This 2026 UK evidence review summarises the biology, the regulatory landscape, the comparison with licensed and adjunctive treatments, and where the evidence is genuinely absent.

ME/CFS in 2026: From Contested Diagnosis to Biologically Defined Disease

For decades, Myalgic Encephalomyelitis / Chronic Fatigue Syndrome (ME/CFS) was the most contested diagnosis in UK medicine. Patients were told their fatigue was deconditioning. Graded exercise therapy was the recommended treatment. Cognitive behavioural therapy was, at one point, claimed as a cure. Severe ME — patients bedbound, tube-fed, unable to tolerate light or sound — was treated with scepticism in some NHS settings. That history is the necessary context for everything that follows.

The picture in 2026 looks very different, for four reasons:

• NICE NG206 (October 2021) removed graded exercise therapy, downgraded CBT to a non-curative supportive role, made post-exertional malaise a required diagnostic feature, and explicitly stated that ME/CFS is not caused by deconditioning, depression or psychological factors.
• Long COVID generated a second, large post-infectious ME/CFS cohort that could not be dismissed. The January 2025 RECOVER analysis showed 4.5% of post-COVID participants met ME/CFS criteria versus 0.6% of uninfected controls, with new ME/CFS cases running approximately 15× pre-pandemic baseline.
• The DecodeME GWAS preprint (August 2025) reported the first robust common-variant genetic architecture for ME/CFS, definitively establishing a biological basis (and pointing to immune and mitochondrial, not psychological, mechanisms).
• The Maeve Boothby O’Neill inquest (July–August 2024) and the subsequent October 2024 Regulation 28 Prevention of Future Deaths report forced UK Government engagement at the highest level and was explicitly referenced in the July 2025 Delivery Plan.

The biology that has emerged is converging on a recognisable picture: a post-infectious, immune-mediated, neuroinflammatory disorder with mitochondrial bioenergetic dysfunction, autonomic dysregulation and centrally mediated exertion intolerance. Patients describe the cognitive component — the ‘brain fog’ covered in the Long COVID review — as the second most disabling symptom after PEM itself. Within this circuit-based view, the question is no longer “is ME/CFS real” but “which biological subgroups exist, and how do we treat each one”. That is the question Dihexa’s mechanism — covered in detail in the mechanism of action guide — was originally engineered to address in Alzheimer’s disease and is now being asked about in many adjacent post-infectious cognitive conditions.

DecodeME August 2025: The First Robust Genetic Architecture of ME/CFS

The single most important neuroscience event of 2025 for ME/CFS was the DecodeME preprint, posted to medRxiv on 6 August 2025. Led by Professor Chris Ponting at the MRC Human Genetics Unit, University of Edinburgh, in partnership with Action for ME and funded jointly by the MRC and NIHR, DecodeME was specifically designed to be the world’s first well-powered (~25,000-case) GWAS of ME/CFS.

The headline findings:

• Recruitment of over 27,000 participants with clinically confirmed ME/CFS via UK and international cohorts.
• Primary GWAS analysis on approximately 15,579 European-ancestry cases versus 259,909 population controls.
• Eight genome-wide significant loci reaching the conventional 5×10^-8 threshold.
• Lead genes near the significant SNPs converge on three biological themes:
  • Innate immunity and viral defence: RABGAP1L, BTN2A2, OLFM4. Each of these genes is involved in response to viral or bacterial infection.
  • Mitochondrial function: FBXL4. Biallelic loss-of-function variants in FBXL4 cause severe mitochondrial DNA depletion syndrome, a known mitochondrial disorder. The common-variant ME/CFS signal in the same gene is biologically striking.
  • Synaptic biology: CA10. Carbonic anhydrase 10 is a synaptic organising molecule that interacts with neurexins.
• A female-only sex-specific signal: three of the six primary loci replicated in a female-only analysis (12,833 cases), while zero loci reached significance in a male-only analysis (2,746 cases). This is among the clearest sex-specific genetic architectures reported in any common disease and likely reflects both real biological differences and the substantially larger female cohort.
• Strong genetic correlation with depression and chronic pain conditions; weaker correlation with classical autoimmune diseases.

The peer-reviewed publication remained outstanding as of May 2026, but the preprint has already reshaped UK research priorities. Expert reaction at the Science Media Centre emphasised three implications:

• The genetic signal supports an infection-susceptibility model of ME/CFS rather than a primary psychological aetiology.
• The mitochondrial finding revives interest in bioenergetic-targeted interventions including coenzyme Q10, NADH and the oxaloacetate programmes covered below.
• The synaptic CA10 signal is intriguing for any compound — including Dihexa — that engages synaptogenesis. Whether it points to a synaptic deficit (which a synaptogenic agent might address) or to a sensitisation/consolidation problem (which a synaptogenic agent might worsen) is not resolved.

The July 2025 UK ME/CFS Delivery Plan: 'My Full Reality'

On 22 July 2025, the Department of Health and Social Care published the final UK ME/CFS Delivery Plan, ‘My Full Reality’. It was the product of multi-year consultation with patient organisations, clinicians and researchers, and was the first time the UK government had committed to a structured response to ME/CFS.

The plan is organised around three pillars and a set of cross-cutting commitments:

• Research. The NIHR Application Development Award scheme provides £200,000 grants for repurposed pharmaceuticals in post-acute infection syndromes including ME/CFS. The MRC PRIME infrastructure programme was launched in 2025 to build UK research capacity. The UKRI ME/CFS Priority Area was announced to coordinate funding across MRC and NIHR.
• Attitudes and education. Optional NHS e-learning modules including a specific severe-ME module; primary-care guidance updates; medical-school curriculum review.
• Living with ME/CFS. Strengthening the existing NHS specialist clinic network; commitment to consider commissioning a severe-ME inpatient service (in response to the Maeve Boothby O’Neill PFD report); accessibility and benefits navigation.

Patient organisations welcomed the publication but flagged structural limitations. Forward-ME, #ThereForME, the ME Association and MEAction noted that:

• There is no new ring-fenced research funding at the scale of need. The historical UK ME/CFS research spend (around £6 million over 2015–2020) compares poorly with £53 million for Parkinson’s disease and £22 million for multiple sclerosis over the same period.
• By late 2025, fewer than 50 NHS staff had completed the severe-ME e-learning module.
• No commissioned NHS service exists for very severe ME in England, Scotland or Northern Ireland. A new integrated ME/CFS service launched in North Wales (Betsi Cadwaladr UHB) in 2025, branching from the existing Long COVID service.
• The £200,000 application development grants are insufficient to fund Phase 2 trials of repurposed agents; they essentially fund grant applications, not the trials themselves.

The Delivery Plan is the policy backdrop against which all of the trials, the DecodeME data, and the research-chemical curiosity discussed on this page is happening. It is a serious advance on previous government engagement, and a long way from being adequate to the scale of need.

February 2024 NIH Walitt Deep-Phenotyping Paper: Central Rather Than Peripheral

On 21 February 2024, the NIH Intramural Research Program published “Deep phenotyping of post-infectious myalgic encephalomyelitis/chronic fatigue syndrome” in Nature Communications (PMC10881493). The lead author was Brian Walitt, working with senior author Avindra Nath. The study enrolled 17 patients with post-infectious ME/CFS (PI-ME/CFS) and 21 healthy controls, and applied an extensive multi-organ phenotyping battery: brain MRI, autonomic testing, immune profiling, cardiopulmonary exercise testing (CPET), muscle physiology, and the Effort Expenditure for Rewards Task (EEfRT) as a behavioural readout of central effort processing.

The headline findings:

• Patients with PI-ME/CFS showed an altered ‘effort preference’ on the EEfRT task — biased toward low-effort low-reward choices — that the authors interpreted as a centrally mediated rather than peripheral fatigue.
• Altered central catechol pathway signalling: reduced cerebrospinal fluid catechol metabolites consistent with reduced central dopamine and noradrenaline drive.
• Immune profiling showed expansion of naive B cells and reduction in switched memory B cells — an immune-aged but immunologically distinct signature.
• Sex-specific differences in immune and autonomic findings.
• No peripheral muscle dysfunction sufficient to explain the fatigue.

The interpretation generated significant controversy in the patient community. The phrase “effort preference” was widely read as implying a behavioural or motivational cause, despite the authors’ explicit statement that it reflects brain dysfunction, not deconditioning, not depression, and not psychogenic illness. The patient critique was that the framing was rhetorically equivalent to the historic ‘PACE-trial era’ assumptions that NICE NG206 had just rejected. Avindra Nath and Walitt issued clarifying statements in subsequent interviews emphasising that the central-fatigue interpretation does not blame the patient and points toward CNS biology as the locus of pathology.

For Dihexa-relevant biology, the Walitt paper is significant for three reasons:

• It identifies a central catechol deficit that, in principle, a synaptogenic agent could plausibly contribute to addressing (the catecholaminergic system is partly dependent on noradrenergic/dopaminergic synaptic plasticity).
• It supports a circuit-based view of post-exertional malaise that locates the ‘effort regulation’ problem in the brain rather than the muscle.
• It reinforces the directionality risk: if effort regulation is centrally tuned and pathologically restrictive, what does a peptide that drives rapid synaptogenesis in those exact circuits do? The honest answer is that nobody knows. This is the same directionality concern raised for fibromyalgia and OCD on this site.

Microglial Neuroinflammation, BDNF and the Synaptogenic Hypothesis of ME/CFS

If there are two molecular findings that anchor the synaptic-plasticity-and-neuroinflammation hypothesis of ME/CFS, they are microglial activation on PET imaging and BDNF dysregulation.

Microglial Activation (Nakatomi 2014; Younger 2025)

The Nakatomi et al. 2014 Journal of Nuclear Medicine paper remains a foundational reference. Using 11C-(R)-PK11195 PET — a first-generation translocator protein (TSPO) ligand — in nine patients with ME/CFS versus ten controls, Nakatomi’s team found significant microglial / astrocytic activation in:

• Cingulate cortex
• Hippocampus
• Thalamus
• Midbrain
• Pons

The hippocampal and cingulate signal correlated with fatigue and cognitive symptom scores. The study has well-known limitations — small sample size, first-generation TSPO ligand, no arterial input function for absolute quantification — but it provided the first imaging evidence of brain neuroinflammation in ME/CFS, and has been replicated conceptually in subsequent work.

In August 2025, the Jarred Younger group at the University of Alabama at Birmingham reported a whole-brain MRI-thermometry / lactate study (covered by Health Rising in August 2025) showing diffuse temperature and lactate elevation across the ME/CFS brain consistent with widespread low-grade neuroinflammation. The strength of MRI thermometry is that it does not require a radioactive tracer and can therefore be repeated in the same individual over time — useful for tracking treatment response in any future ME/CFS trial.

If microglial activation is causal rather than merely correlative, it points toward several therapeutic targets: TLR4 modulation (the LDN mechanism discussed below), TSPO ligands, microglial calming agents such as low-dose naltrexone, palmitoylethanolamide, minocycline, and centrally penetrant anti-inflammatories.

BDNF Hypomethylation and Elevated Peripheral BDNF (Polli 2020)

The seminal BDNF paper in ME/CFS is Polli et al. 2020 in Arthritis & Rheumatology: “DNA Methylation and Brain-Derived Neurotrophic Factor Expression Account for Symptoms and Widespread Hyperalgesia in Patients With CFS and Comorbid Fibromyalgia” (PMID 32562379). In 28 patients with CFS plus comorbid fibromyalgia versus 26 controls, Polli found:

• Hypomethylation of the BDNF gene at specific CpG sites.
• Elevated serum BDNF protein.
• Correlation between elevated BDNF and symptom severity, widespread hyperalgesia and conditioned pain modulation deficits.

The directionality is the same paradox covered in the dedicated fibromyalgia review: BDNF is elevated, not deficient, in the periphery in CFS-with-fibromyalgia. That is the opposite of the BDNF deficit pattern in depression, Alzheimer’s disease and the post-stroke recovery setting where synaptogenic BDNF-augmenting interventions are theoretically attractive. In ME/CFS-with-fibromyalgia, the picture is more complicated: peripheral BDNF elevation could be driving the central sensitisation, the chronic pain and the cognitive symptoms; in which case a peptide that further engages BDNF-convergent plasticity pathways could plausibly worsen rather than improve symptoms. A 2022 medRxiv preprint linked high BDNF with low psychological flexibility and fatigue symptoms in a separate ME/CFS-adjacent cohort.

The relevant question for Dihexa is whether the central versus peripheral BDNF compartment matters. The honest answer is that it almost certainly does, but the directionality of central BDNF in ME/CFS (as opposed to peripheral serum BDNF) has not been adequately characterised by 2026 standards. This is biologically important: a peptide intervention that elevates central BDNF in the prefrontal cortex (good for executive function) but also amplifies central sensitisation in the pain matrix and PEM circuits (potentially harmful) is the kind of net-effect uncertainty that ME/CFS desperately needs trials to resolve.

The full mechanistic and potency comparison with BDNF, including the interpretation of the often-quoted “10 million times more potent” figure, is in the Dihexa vs BDNF deep-dive.

NICE NG206 and the Removal of Graded Exercise Therapy

The UK regulatory backbone of ME/CFS care is NICE NG206 (Myalgic encephalomyelitis (or encephalopathy)/chronic fatigue syndrome: diagnosis and management), published on 29 October 2021. No major update had been issued by May 2026.

The headline content:

• Post-exertional malaise (PEM) is a required diagnostic feature, alongside debilitating fatigue not relieved by rest, unrefreshing sleep, and either cognitive impairment or orthostatic intolerance.
• Three-month symptom duration is required for diagnosis; clinical investigation should be pursued during this period rather than after.
• Graded exercise therapy (GET) is not to be offered as a treatment. NICE explicitly rejected the evidence base on grounds of low quality and risk of harm.
• Cognitive behavioural therapy is not a cure. CBT is recommended only as a supportive coping framework, with the explicit caveat that it should not be presented to patients as treating the underlying illness.
• Pacing and energy management — with reference to the patient-led concept of the ‘energy envelope’ — are the foundation of treatment.
• Symptomatic management of orthostatic intolerance, sleep, pain, mood and cognitive symptoms is recommended.
• Referral to a specialist clinic is recommended where available.
• ME/CFS is not caused by deconditioning, depression or psychological factors.
• Special provisions for severe and very severe ME, including avoidance of bright light, sound and unnecessary movement; recognition that hospitalisation may be required and that some patients cannot tolerate standard hospital environments.

NG206 is a substantial corrective to the previous CG53 (2007), and reflects the patient-community-driven evidence reanalysis of the PACE trial and the subsequent change in international consensus. The clinical implication is that any future trial of a synaptogenic agent in ME/CFS will need to respect PEM physiology: trial designs that require any form of exertion challenge will need to monitor for, and protect against, post-exertional symptom exacerbation.

The Maeve Boothby O'Neill Inquest and the October 2024 Prevention of Future Deaths Report

The single most consequential event for UK ME/CFS policy in 2024 was the inquest into the death of Maeve Boothby O’Neill, a young woman with very severe ME who died in Devon in 2021 after a prolonged period of inability to tolerate adequate nutrition. The inquest concluded in July–August 2024, and on 7 October 2024 Assistant Coroner Deborah Archer issued a Regulation 28 Prevention of Future Deaths report directed at NHS England, the Department of Health and Social Care, NICE and three other parties.

The report identified specific concerns:

• No specialist hospital or hospice provision for very severe ME in England.
• Lack of training across NHS clinical staff in recognising and managing very severe ME, including its tolerance limitations (light, sound, movement, oral intake).
• Underfunding of research into the condition.
• Variability in the quality of NHS specialist clinics, with some operating at long waiting times and others closed entirely.
• Specific concerns about decision-making capacity assessment in patients too ill to communicate verbally.

The 25% ME Group, Forward-ME, ME Association and #ThereForME campaign continued to use the Maeve PFD report as the central reference point for ongoing advocacy through 2025 and into 2026, including the request that NHS England commission a severe-ME inpatient service. The Delivery Plan (July 2025) referenced the PFD report in its commitment to consider commissioning specialist provision, but no commissioned service had been announced by May 2026.

For anyone reading this page who is housebound, bedbound or otherwise severely affected: please contact the 25% ME Group, the Action for ME severe-ME service, or the ME Association ME Connect helpline. Self-experimentation with research peptides in this population is particularly inadvisable, both because of the additional health risks and because of the absence of any specialist supervision capacity should adverse events occur.

The 2025 ME Association / UBC Low-Dose Naltrexone Trial

The single most-watched ME/CFS pharmacology event of 2025–2026 is the low-dose naltrexone (LDN) trial at the University of British Columbia Complex Chronic Diseases Program (CCDP), led by Dr Luis Nacul (also affiliated with the London School of Hygiene & Tropical Medicine).

The trial is a double-blind, randomised, placebo-controlled study of LDN 1.0–4.5 mg versus placebo in patients with post-COVID fatigue syndrome with ME/CFS overlap (NCT05430152). Primary outcomes are fatigue, post-exertional malaise and inflammatory biomarkers. In April 2025, the ME Association announced a £132,000 investment to support recruitment and follow-up on top of the existing Canadian Institutes of Health Research funding.

The mechanistic rationale for LDN is:

• TLR4 antagonism on microglia at low doses (typically 1.0–4.5 mg, well below the opioid-blocking dose of 50 mg). The Younger group has argued that low-dose naltrexone calms microglial activation in the chronic-pain and chronic-fatigue circuits.
• Endogenous opioid rebound. Brief opioid receptor blockade overnight is hypothesised to lead to upregulation of endogenous opioid signalling during the rest of the 24-hour cycle.
• TRPM3 ion channel restoration. A 2025 mechanistic paper (PMC12127304) found that LDN restored TRPM3 channel function in natural killer cells from Long COVID patients, providing a NK-cell-specific molecular basis distinct from the TLR4 mechanism.

As of October 2025, 208 participants had been pre-recruited, 123 dosed and 76 completed protocol; trial completion was expected by 31 December 2025 with full results in 2026. The earlier observational and small-RCT evidence base for LDN in ME/CFS is the Bolton et al. 2020 case series and the May 2025 Annals of Medicine and Surgery LDN systematic review and meta-analysis covered in detail in the fibromyalgia review.

In the UK, LDN is not licensed for ME/CFS and is most commonly accessed via Dickson Chemist in Glasgow as a special-order or specials prescription on a private basis (private prescriber required; cost approximately £30–50 per month). NHS ICB funding for LDN remains variable and patient-specific.

Other 2024-2026 ME/CFS Treatment Programmes

The Delivery Plan and the DecodeME data are accelerating, but the pharmacological landscape remains thin. The notable programmes:

• Rintatolimod (Ampligen). AIM ImmunoTech’s TLR3 agonist remains FDA unapproved in the US and unapproved in the UK. The January 2025 AMP-518 readout in Long COVID-associated fatigue was modest. No UK access via NHS or specials.
• BC 007 (Berlin Cures). The aptamer-based GPCR autoantibody scavenger Phase 2 trial in Long COVID failed its primary endpoint in November 2024; the company subsequently halted development.
• Oxaloacetate. The RESTORE-ME RCT (Cash & Kaufmann 2024 in Frontiers in Neurology, PMC11632837) reported positive fatigue outcomes in ME/CFS; the REGAIN trial extended this to Long COVID in 2025. Oxaloacetate is available as a supplement but not as a licensed medicine.
• Coenzyme Q10 plus NADH. The Castro-Marrero et al. 2021 double-blind RCT (n=207, PMC8399248) reported improvements in fatigue, health-related quality of life and sleep with 200 mg CoQ10 + 20 mg NADH for 12 weeks. The 2024 Castro-Marrero review in International Journal of Molecular Sciences (PMC10779395) provides the mitochondrial-dysfunction context.
• Pyridostigmine (Mestinon). The David Systrom group at Brigham & Women’s Hospital has championed pyridostigmine for preload-failure POTS and ME/CFS based on invasive cardiopulmonary exercise testing. Not licensed for this indication; available on private prescription in the UK.
• Low-dose aripiprazole. The Crosby 2021 observational case series reported symptom improvement on 0.2–2.0 mg aripiprazole; no RCT has been published to confirm this.
• Rapamycin. Open-label observational use only; no controlled trial data in ME/CFS.
• Cortene CT38. A small InTime trial closed; no further development announced.
• Beta-blockers (propranolol, ivabradine). Used symptomatically for POTS and inappropriate sinus tachycardia in ME/CFS.

None of these is licensed by the MHRA specifically for ME/CFS in 2026. The Delivery Plan’s NIHR Application Development Awards are specifically intended to support repurposed-pharmaceutical applications in this category, but the application volume is small and the funding ceiling is low.

Long COVID and ME/CFS Overlap

The COVID-19 pandemic produced the largest single-cohort epidemiological natural experiment in post-infectious ME/CFS biology. The evidence is now consistent:

• Wong & Weitzer 2021 in Medicina: systematic review finding 25 of 29 ME/CFS symptoms reported in Long COVID populations.
• Dehlia & Guthridge 2024 in Journal of Infection: meta-analysis estimating approximately 51% of Long COVID patients meet ME/CFS criteria.
• RECOVER January 2025 (Vernon et al.): 4.5% of post-COVID participants met ME/CFS criteria versus 0.6% of uninfected controls; new ME/CFS cases approximately 15× pre-pandemic baseline.
• UK NHS Long COVID service data through 2025 shows substantial proportions of post-COVID-19 syndrome patients fulfilling NICE NG206 criteria when assessed against PEM and PEM-equivalent post-exertional symptom exacerbation (PESE).

The clinical implication is that the ME/CFS biology evidence base is now effectively shared with the Long COVID research community. The DecodeME data, the Walitt deep-phenotyping paper, the microglial-activation imaging and the BDNF biology described above are increasingly being treated as relevant to both populations. Discussion of Long COVID brain fog, including the PESE concept and the LDN trial overlap, is covered in the dedicated Long COVID review.

The ME/CFS Comorbidity Cluster: Fibromyalgia, POTS, MCAS, Long COVID, Mood and Migraine

ME/CFS rarely travels alone. Anyone presenting with ME/CFS should be considered against the backdrop of a well-characterised comorbidity cluster:

• Fibromyalgia. Approximately 30–70% of ME/CFS patients meet fibromyalgia criteria on the ACR 2016 widespread pain index. The shared central sensitisation, BDNF elevation and small-fibre neuropathy biology is covered in the Dihexa for fibromyalgia review.
• POTS and dysautonomia. Postural orthostatic tachycardia syndrome is highly comorbid. Heart-rate variability is reduced; orthostatic intolerance is one of the four NICE NG206 alternative diagnostic features.
• Mast cell activation syndrome (MCAS). A subset of patients show pronounced histaminergic, flushing, GI and skin features consistent with MCAS; H1/H2 blocker trials are common.
• Long COVID. ~50% of Long COVID patients meet ME/CFS criteria (Dehlia 2024). Covered in the Long COVID brain fog review.
• Hypermobile Ehlers-Danlos syndrome (hEDS). The hEDS-POTS-MCAS triad is over-represented in ME/CFS cohorts.
• Depression and anxiety. Common but explicitly secondary in NICE NG206 (not causal). Bidirectional. Covered in the Dihexa depression review and the Dihexa anxiety review.
• Migraine. Substantially over-represented compared with the general population.
• IBS and small intestinal bacterial overgrowth (SIBO). Common; gut-brain axis interest in the post-infectious context.
• Endometriosis. Over-represented; shared inflammatory biology.
• Menstrual cycle and menopausal worsening. Many female patients describe perimenstrual and perimenopausal worsening — the menopause overlap is covered in the menopause brain fog review.
• Sleep apnea. A surprising fraction of ME/CFS-spectrum patients have undiagnosed mild OSA contributing to fatigue and brain fog; covered in the Dihexa for sleep apnea review.
• Mild cognitive impairment. The long-term cognitive trajectory of severe long-standing ME/CFS overlaps with MCI; covered in the Dihexa for MCI and brain aging review.

The cognitive picture in any individual ME/CFS patient is rarely ‘pure’. By the time most patients present, they have some combination of central sensitisation, autonomic dysregulation, sleep architecture disruption and mood comorbidity layered on top of the core PEM-and-fatigue phenotype. This is why a single intervention — pharmacological or otherwise — rarely produces total remission, and why the most robust UK ME/CFS clinics combine pacing, autonomic support, sleep restoration, mood management and symptomatic medication.

Cognitive Dysfunction and 'Brain Fog' in ME/CFS

Approximately 85–90% of ME/CFS patients report significant cognitive dysfunction. The pattern is consistent across multiple cognitive batteries (Cockshell & Mathias 2010 meta-analysis; Bansal et al.; Robinson 2025 UK series):

• Information processing speed is the most consistently affected domain.
• Working memory is impaired, particularly under cognitive load and over time.
• Sustained and divided attention deteriorate with task duration — the cognitive analogue of PEM.
• Word-finding difficulty and verbal fluency are widely reported.
• Executive function — planning, task-switching, inhibitory control — is affected.
• Encoding rather than consolidation appears to be the dominant memory problem; long-term consolidated memory is relatively spared.

The structural correlates are still being characterised. Smaller-volume hippocampal MRI findings in ME/CFS have been reported but with substantial heterogeneity. Resting-state fMRI work has consistently shown altered default mode network connectivity. PET imaging suggests the cingulate-hippocampal-thalamic-midbrain circuit hit by microglial activation overlaps substantially with the circuitry of attention and executive function. The 2025 reviews from MDPI Brain Sciences (February 2025) and Trends in Neurosciences (March 2025) have synthesised the literature.

For Dihexa, the cognitive profile is the part of ME/CFS biology where a synaptogenic, HGF/c-Met-engaging compound is most plausibly relevant. Information processing speed, working memory and sustained attention are exactly the domains where rapid synaptogenesis in prefrontal and hippocampal circuits could in principle help. The same population, though, is the population at highest PEM risk — and any cognitive challenge associated with measuring whether a peptide is working is itself a PEM trigger.

Where Dihexa Fits the ME/CFS Picture

Dihexa is a small-molecule peptide analogue developed from angiotensin IV (Nle¹-AngIV). Its mechanism, covered in full in the mechanism of action guide, has three features relevant to ME/CFS:

• Direct HGF/c-Met activation. The hepatocyte growth factor / c-Met receptor system is widely expressed in cortex, hippocampus and cerebral microvasculature, and is one of the strongest endogenous drivers of both synapse formation and angiogenic repair (Wright & Harding 2015; Benoist 2014).
• Rapid spine formation. Dihexa has been reported to induce new dendritic spines within hours in cell-culture and slice-physiology preparations.
• Blood-brain barrier penetration. Unlike BDNF or recombinant HGF, Dihexa was engineered for oral bioavailability and central penetration.

Within the synaptic-plasticity-and-neuroinflammation model of ME/CFS, that mechanistic profile is appealing for the cognitive component:

• Microglial activation has been documented (Nakatomi 2014; Younger 2025). HGF/c-Met has anti-inflammatory effects on microglia in some preclinical contexts.
• Cognitive symptoms are dominant. Synaptogenic effects in prefrontal cortex and hippocampus are exactly what an information-processing-speed deficit might respond to.
• Vascular and BBB dysfunction is described in subgroups. HGF/c-Met supports endothelial repair and BBB integrity.
• The DecodeME synaptic CA10 signal raises (without resolving) the question of whether synaptic biology is impaired or hyperactivated in ME/CFS.

On the other hand, three concerns are real and serious:

• PEM directionality risk. If post-exertional malaise involves pathologically strengthened sensorimotor and limbic circuits that consolidate the post-exertional response, a peptide that drives rapid synaptogenesis in those circuits could plausibly worsen rather than relieve the cardinal feature of the illness. There is no human evidence in either direction.
• BDNF directionality paradox. Peripheral BDNF is elevated, not deficient, in ME/CFS-with-fibromyalgia (Polli 2020). Whether central BDNF in PFC and hippocampus is elevated or reduced is not adequately characterised.
• c-Met oncogenicity in long-term dosing. Sustained c-Met activation is a known driver of tumour growth in several solid cancers. Long-term safety in any ME/CFS population — many of whom are young, female, and may be on the illness for decades — has not been studied.

The translational gap is the same as for anxiety, depression and most other conditions covered on this site. No published clinical trial has tested Dihexa in any ME/CFS, post-viral fatigue, post-exertional malaise or Long COVID population. No open-label series exists in the peer-reviewed literature. The closest clinical relative — fosgonimeton (ATH-1017) — was developed for Alzheimer’s disease and did not test ME/CFS endpoints; its Phase 3 LIFT-AD trial did not meet its primary cognitive endpoint in September 2024, and the SHAPE programme in Parkinson’s disease dementia and dementia with Lewy bodies was subsequently discontinued. A plausible mechanism is a reason to investigate, not evidence of effect, and decades of cognitive-enhancement drug development is full of compounds that worked in animal models and failed in humans.

The UK NHS ME/CFS Pathway and Where Patients Are Looking

The current UK ME/CFS pathway is broadly:

• Primary care assessment. History, examination, basic blood screen to exclude alternative diagnoses (anaemia, hypothyroidism, coeliac disease, B12/folate, vitamin D, liver and renal function, inflammatory markers, ferritin, HbA1c, fasting glucose). If symptoms persist after three months with PEM and other NICE NG206 features, ME/CFS diagnosis can be made.
• Referral to specialist clinic where available. England has 50+ NHS adult ME/CFS clinics of variable quality and waiting times; some paediatric services. North Wales now has a new integrated service (2025). Rest of Wales, Scotland and Northern Ireland have no commissioned specialist service.
• Pacing and energy management. Often delivered via occupational therapy or specialist clinic; patient-led pacing apps and the ‘energy envelope’ concept.
• Symptomatic management. Orthostatic intolerance (increased fluid and salt; compression garments; ivabradine, beta-blockers, midodrine, fludrocortisone, pyridostigmine off-label where appropriate). Sleep (sleep hygiene; melatonin; low-dose amitriptyline). Pain (non-pharmacological where possible; amitriptyline or duloxetine where required under NG193 chronic primary pain).
• Cognitive support. Pacing of cognitive activity; environmental adjustments; speech and language therapy referral where word-finding is severe.
• Severe and very severe ME provision. Limited; the Maeve PFD report and Delivery Plan acknowledge the gap. Home visits, severe-ME e-learning module for NHS staff, charity helpline support.
• Benefits navigation. Personal Independence Payment (PIP), Employment Support Allowance (ESA), Universal Credit Limited Capability for Work assessments. Action for ME and ME Association provide written guidance.

The result is a population of people who: have been on a specialist clinic waiting list for over a year, are pacing but still significantly affected, have tried off-label LDN privately, may be considering CoQ10 or oxaloacetate as supplements, and are looking for ‘the next thing’. That curiosity drives traffic to research-chemical pages like this one. It is also the reason this article is written as a careful evidence summary rather than a sales pitch.

Specific Risks of Self-Experimenting with Dihexa in ME/CFS

Even among the conditions covered on this site, ME/CFS carries specific risks that make self-experimentation particularly inadvisable:

• PEM amplification. The single most plausible adverse outcome. A peptide that drives rapid synaptic strengthening in already-sensitised circuits could amplify post-exertional malaise. Severe PEM can persist for weeks and is not always fully reversible.
• Masking diagnosis. A patient who attributes their fatigue and brain fog to ME/CFS but is in fact treating an undiagnosed alternative (B12 deficiency, hypothyroidism, sleep apnea, coeliac disease, Long COVID with treatable POTS) may delay essential investigation by self-medicating.
• Multi-drug interaction risk. ME/CFS patients are disproportionately on multiple symptomatic medications: SSRIs, SNRIs, low-dose amitriptyline, gabapentin, pregabalin, beta-blockers, ivabradine, pyridostigmine, LDN. None of these has documented interaction data with Dihexa.
• Severe and very severe ME population particularly vulnerable. Reduced ability to communicate adverse effects, reduced tolerance to any stimulus, and absence of specialist supervision make experimentation in this group particularly dangerous.
• Female patient population. 75–85% of ME/CFS patients are women, many of whom may be of reproductive age. No pregnancy, lactation or fertility safety data for Dihexa exists.
• Long-term safety unknown. ME/CFS is often a multi-decade illness. Cumulative exposure to sustained c-Met activation has not been characterised in any human population over that timescale.
• Mood destabilisation. Covered in the depression and bipolar disorder reviews.
• Cost. The cost of research peptides over months to years can be substantial and may displace funding for evidence-based supports (private LDN prescription, occupational therapy, home adaptations).

A Reasonable Non-Peptide Approach to ME/CFS Cognitive Symptoms

Anyone reading this page for solutions, rather than for the science, should consider that the evidence-based components of ME/CFS care — in approximate order of effect size for cognitive symptoms specifically — are well defined:

• Pacing and energy management. The single highest-yield intervention for almost all ME/CFS-spectrum patients. Reduces PEM frequency, severity and the cumulative cognitive load that drives brain fog.
• Exclude alternative diagnoses. A full blood screen and consideration of sleep apnea, vitamin deficiencies, thyroid disease and Long COVID. The sleep apnea review covers the overlap.
• Address orthostatic intolerance. Increased fluid and salt; compression garments; pharmacological support where appropriate. Many cognitive symptoms attributed to ME/CFS are actually driven by cerebral hypoperfusion in standing.
• Restore sleep architecture. CBT-I where appropriate, low-dose amitriptyline, melatonin. Sleep restoration produces some of the largest single-intervention cognitive gains in the literature.
• Try evidence-based supplements with caution. CoQ10 + NADH has RCT support (Castro-Marrero 2021); oxaloacetate has RCT support (Cash & Kaufmann 2024). Many ME/CFS patients trial these. The effect sizes are modest but real.
• Consider LDN under specialist supervision. The UBC trial readout will clarify the evidence; private UK access via Dickson Chemist Glasgow is the most common route in 2026.
• Treat comorbid mood, anxiety and pain. Symptomatic relief of these conditions reduces perceived cognitive symptoms even where the underlying ME/CFS biology is unchanged.
• Reduce overall cognitive demand. Workplace accommodations, reduced screen time, environmental simplification. The Equality Act 2010 requires reasonable adjustments for ME/CFS as a long-term health condition.
• Engage with patient organisations. The Action for ME and ME Association ME Connect helplines provide signposting and specialist referrals.
• Consider trial enrolment. The UK NIHR Be Part of Research portal lists current ME/CFS and Long COVID studies. Participation contributes to the data that will eventually answer the questions this page cannot.

An unscheduled research chemical with no human ME/CFS data is not a substitute for any of the above. It might one day, in a structured trial of patients with adequately paced ME/CFS but persistent cognitive symptoms, become an adjunct that supports residual recovery. It is not currently that.

The Bottom Line in 2026

Dihexa fits parts of the modern biological model of ME/CFS with reasonable mechanistic precision. Microglial neuroinflammation, BDNF dysregulation, mitochondrial dysfunction and centrally mediated effort regulation — the four main biological themes that emerged from DecodeME, the Walitt deep-phenotyping paper, the Nakatomi PET data, the Younger MRI thermometry work and the Polli BDNF series — are all biology that the HGF/c-Met system is, in principle, capable of engaging. A BBB-penetrant compound that drives synaptogenesis and supports endothelial repair in cortex, hippocampus and limbic circuits is, at the level of theory, the kind of agent ME/CFS neuroscience has been hoping someone will eventually develop and trial.

The other half of the picture is the directionality problem. Post-exertional malaise is the cardinal feature of ME/CFS, and its central neurobiology — not yet fully understood — appears to involve pathological strengthening, not weakening, of sensorimotor and limbic responses to exertion. A synaptogenic peptide that drives rapid spine formation in those exact circuits could in principle worsen rather than relieve the core feature of the illness. The same directionality risk applies in fibromyalgia, OCD and tinnitus. Without trial data, the net effect in ME/CFS cannot be predicted.

Theory is where the evidence stops. There is no human trial of Dihexa in ME/CFS, post-exertional malaise, post-viral fatigue syndrome or Long COVID. There is no published case series, no biomarker data, no controlled comparisons against pacing, low-dose naltrexone, CoQ10/NADH or pyridostigmine, no interaction studies with the SSRIs, beta-blockers and analgesics that ME/CFS patients are often on, and no long-term safety data in chronically dosed female patients of reproductive age. The closest clinical relative fosgonimeton was developed for Alzheimer’s disease, not ME/CFS, and its 2024 Phase 3 readout did not meet its primary endpoint. Community self-reports are heterogeneous and do not rise above the quality threshold of hypothesis-generation.

For anyone with significant ME/CFS reading this in 2026, the honest reading of the evidence is: Dihexa is biologically interesting on the neuroinflammation and cognitive side, biologically risky on the post-exertional-malaise side, and clinically unverified. It cannot currently be recommended for ME/CFS. Evidence-based interventions — pacing and energy management, orthostatic and sleep management, treatment of comorbid mood and pain, supervised consideration of LDN, CoQ10 and oxaloacetate, and enrolment in trials — are the routes with measurable human effect sizes. If you are curious about Dihexa as a compound, the what is Dihexa, benefits and research and studies pages are the right starting points. If your ME/CFS is severe and unsupported, please contact Action for ME, the ME Association or the 25% ME Group.

Frequently Asked Questions

Selected References & Outbound Sources

1. Action for ME. UK patient charity: prevalence, helpline, severe ME service, advocacy. Accessed May 2026.
2. ME Association. UK patient charity: ME Connect helpline 0344 576 5326, research news, clinical updates. Accessed May 2026.
3. Ponting CP, DecodeME Steering Committee, Action for ME et al. Initial findings from the DecodeME genome-wide association study of myalgic encephalomyelitis/chronic fatigue syndrome. medRxiv preprint, 6 August 2025. DOI: 10.1101/2025.08.06.25333109.
4. UK Department of Health and Social Care. My Full Reality: the final UK ME/CFS Delivery Plan. 22 July 2025.
5. Walitt B, Singh K, LaMunion SR et al. Deep phenotyping of post-infectious myalgic encephalomyelitis/chronic fatigue syndrome. Nature Communications, 21 February 2024. DOI: 10.1038/s41467-024-45107-3. PMC10881493.
6. Nakatomi Y, Mizuno K, Ishii A et al. Neuroinflammation in patients with chronic fatigue syndrome/myalgic encephalomyelitis: an 11C-(R)-PK11195 PET study. J Nucl Med, 2014;55(6):945-50.
7. Younger J. UAB Birmingham brain neuroinflammation thermometry MRI study in ME/CFS — community coverage. Health Rising, August 2025.
8. Polli A, Ghosh M, Bakusic J et al. DNA Methylation and Brain-Derived Neurotrophic Factor Expression Account for Symptoms and Widespread Hyperalgesia in Patients With CFS and Comorbid Fibromyalgia. Arthritis Rheumatol, 2020. PMID 32562379.
9. ME Association. Press Release: Leading UK Charity invests in Canadian trial of drug treatment for ME/CFS and Long COVID (LDN, Nacul/UBC). April 2025.
10. ClinicalTrials.gov. NCT05430152 - Low-Dose Naltrexone for Post-COVID-19 Fatigue Syndrome (UBC, Nacul).
11. Archer D (Assistant Coroner). Maeve Boothby O'Neill: Prevention of Future Deaths report (Regulation 28). 7 October 2024.
12. National Institute for Health and Care Excellence (NICE). Myalgic encephalomyelitis (or encephalopathy)/chronic fatigue syndrome: diagnosis and management (NG206). October 2021.
13. Wong TL, Weitzer DJ. Long COVID and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): A Systemic Review and Comparison of Clinical Presentation and Symptomatology. Medicina, 2021;57(5):418.
14. Dehlia A, Guthridge MA. The persistence of SARS-CoV-2 in tissues and its association with long COVID symptoms: a cross-sectional cohort study in China — meta-analysis of ME/CFS overlap in Long COVID. Journal of Infection, 2024.
15. Vernon SD, Funk S, Bateman L et al. RECOVER analysis - COVID-19 increases risk of developing ME/CFS. January 2025.
16. Castro-Marrero J, Segundo MJ, Lacasa M et al. Effect of Coenzyme Q10 Plus Nicotinamide Adenine Dinucleotide Supplementation on Fatigue Perception and Health-Related Quality of Life in Individuals with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Prospective, Randomized, Double-Blind, Placebo-Controlled Trial. Antioxidants, 2021. PMC8399248.
17. Castro-Marrero J et al. Mitochondrial Dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome — review (EUROMENE consortium). Int J Mol Sci, 2024;25(1):574. PMC10779395.
18. Cash A, Kaufmann DA, Vernon SD. Anhydrous enol-oxaloacetate reduces ME/CFS fatigue in the RESTORE-ME randomised controlled trial. Frontiers in Neurology, 2024. PMC11632837.
19. UKRI / MRC. UKRI ME/CFS Priority Area. 2025.
20. Betsi Cadwaladr UHB. New service launches in North Wales to support people with ME/CFS. 2025.
21. 25% ME Group. UK charity for severe and very severe ME. Accessed May 2026.
22. #ThereForME. UK campaign for ME/CFS NHS reform. Accessed May 2026.
23. NIHR. Be Part of Research: UK ME/CFS and Long COVID trial portal. Accessed May 2026.
24. Wright JW, Harding JW. The brain hepatocyte growth factor/c-Met receptor system: a new target for the treatment of Alzheimer's disease. J Alzheimers Dis, 2015.
25. Benoist CC, Kawas LH, Zhu M et al. The procognitive and synaptogenic effects of angiotensin IV-derived peptides are dependent on activation of the hepatocyte growth factor/c-Met system. J Pharmacol Exp Ther, 2014.
26. Science Media Centre. Expert reaction to the DecodeME GWAS preprint. August 2025.
27. ME Association. MDPI Brain Sciences review of cognitive dysfunction in ME/CFS: aetiology and potential treatments. February 2025.
28. ME Association. Trends in Neurosciences: Cognitive dysfunction (brain fog) in various medical conditions including ME/CFS and Long COVID. March 2025.