Dihexa for Iron Deficiency & Anaemia Brain Fog: Low Ferritin, the 2025 Perimenopause Iron Study, Dopamine, Myelin & the 2026 UK Review

Iron deficiency is the most common nutritional deficiency in the world, and "brain fog" — poor concentration, mental fatigue and a slowed, effortful quality of thinking — is one of its earliest and most under-recognised effects. In April 2025, a University of Oklahoma team reported in Nutrients that women in the menopause transition whose blood iron was simply "below expected" for their age — not even clinically deficient, and none of them anaemic — performed measurably worse on memory, attention and cognition than those with adequate iron. The biology is direct: iron is the essential cofactor for tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis, and for the oligodendrocytes that build myelin, and in animal models iron deficiency downregulates hippocampal BDNF — the same plasticity endpoint that Dihexa, a positive modulator of HGF/c-Met synaptogenesis, also reaches. That overlap is exactly why people ask whether a synaptogenic peptide belongs in the conversation. This 2026 UK review walks through the new Oklahoma data, iron deficiency without anaemia, the dopamine-myelin-BDNF mechanism, the treatment evidence in non-anaemic women, who is at risk, and where Dihexa actually sits — which is behind a ferritin test and a course of iron, not in front of it.

Iron Deficiency and Brain Fog in 2026: The Commonest Deficiency, the Quietest Symptom

Iron deficiency is the most common nutritional deficiency on earth, and in the UK it is strikingly common in exactly the people most likely to complain of brain fog. A 2025 UK analysis of health-aware adults found that almost one in ten women were anaemic, with anaemia most common in those aged 18–50, and that nearly one in three women had absolute iron deficiency. Iron deficiency without anaemia is more common still. For a symptom as widespread as brain fog, iron is one of the first things worth ruling in or out — and one of the most frequently overlooked.

Iron matters to the brain out of all proportion to the tiny amounts involved. It is the cofactor at the centre of three systems that bear directly on clear thinking: dopamine synthesis (iron activates tyrosine hydroxylase, the rate-limiting enzyme), myelination (oligodendrocytes need iron to build and maintain the insulating sheath around nerve fibres), and oxygen delivery (haemoglobin, when deficiency tips into anaemia). When iron runs low, attention, processing speed, working memory and motivation are the cognitive domains that suffer first — precisely the ones patients describe as "fog".

That cognitive symptom is not folklore. The NHS overview of iron deficiency anaemia lists tiredness and lack of energy, and difficulty concentrating, among the core symptoms, alongside breathlessness, palpitations and pale skin. NICE Clinical Knowledge Summaries frame the diagnosis around the full blood count and serum ferritin and stress that, in adults, the deficiency must be investigated, not merely corrected — a point that turns out to matter enormously for the Dihexa question.

What makes iron deficiency unusual among the conditions reviewed on this site is how tractable it is — and how revealing. It is detected with an inexpensive blood test, treated with cheap, widely available iron, and, in adults, frequently reversible. But unlike most causes of brain fog, an iron deficiency in an adult is also a clue: it can be the first sign of slow gastrointestinal blood loss, which is why the work-up reaches beyond the supplement bottle. The patient-facing question echoes the one running through the nutritional posts elsewhere on this site — the B12 deficiency review and the coeliac review: "my brain fog has a real, documented biological cause — does something like Dihexa belong anywhere in the conversation?" In iron deficiency, more than almost anywhere, the honest answer turns on a single fact: the cause is a missing mineral, and you can simply put it back — while finding out where it went.

The April 2025 Oklahoma Study: "Below Expected" Iron and the Perimenopausal Brain

The most important recent piece of evidence in this area — and the reason iron and the brain were back in the headlines in 2025 — is a University of Oklahoma study published in the journal Nutrients (2025; 17(5): 745), titled "Cognitive Performance in Relation to Systemic and Brain Iron at Perimenopause". The researchers examined iron status and cognition in women going through the menopause transition — a window when monthly blood loss can still deplete iron even as it becomes erratic.

The provocative finding is in who was affected. As lead investigators emphasised, none of the women in the study were iron-deficient by standard criteria, and none were anaemic. Yet a substantial number had serum ferritin below what would be expected for their age and background — the cohort's mean serum ferritin sat around 62 µg/L, in the 40th percentile — and it was these women who performed worse on measures of memory, attention and cognition. In other words, the cognitive cost of low iron began well above the line that defines "deficiency".

The study made a second, reassuring point that is just as important for anyone tempted to "boost" iron aggressively. Using brain imaging, the team found that having sufficient iron in the blood did not translate into unsafe iron accumulation in the brain — the kind of brain-iron overload that has been linked to neurodegenerative diseases such as Alzheimer's. Adequate systemic iron supported cognition without raising brain-iron risk, which strengthens the case for correcting a genuine deficiency while cautioning against indiscriminate high-dose supplementation.

Iron Deficiency Without Anaemia: Why a "Normal" Blood Count Misses It

One reason iron-related brain fog is so often missed — and why people with genuine symptoms are sometimes told their bloods are "fine" — is that the routine test most people receive is the full blood count, which flags anaemia, not iron status. Iron deficiency progresses in stages: stores fall first (measured by ferritin), then the iron available to make new red cells drops (measured by transferrin saturation), and only at the end does haemoglobin fall far enough to be called anaemia. The brain, with its high and constant demand for iron, can feel the squeeze during those earlier stages — which is why iron deficiency without anaemia is a real and recognised cause of fatigue and cognitive symptoms.

This is not a fringe idea. Beyond the Oklahoma perimenopause data, a systematic review in the Journal of Nutritional Science examined iron deficiency, cognition, mental health and fatigue in women of childbearing age and found consistent associations even in the absence of anaemia. Work in other groups points the same way: a 2025 imaging study linked iron deficiency without anaemia to reduced basal-ganglia iron content in young people, and a 2025 study in children associated iron deficiency without anaemia with cognitive impairment.

The practical message for anyone with brain fog who has been reassured by a "normal" blood count is to ask specifically about ferritin (with a CRP to interpret it, because ferritin rises with inflammation) and transferrin saturation — and not to conclude that a normal haemoglobin has ruled iron out. It is the same logic as the active-B12 argument in the B12 review: the routine number can sit comfortably "in range" while the tissue that matters is starved.

The Dopamine–Myelin Mechanism: How Low Iron Reaches the Synapse

For the Dihexa-specific question, the decisive biology is the chain that links a missing mineral to a malfunctioning brain — and iron sits at several of its key nodes at once. A 2025 review in Annals of Medicine sets out how central iron is to brain development, ageing and neurodegeneration; three threads matter most for brain fog.

Dopamine. Iron is a required cofactor for tyrosine hydroxylase, the rate-limiting enzyme that converts tyrosine into the dopamine precursor L-DOPA. Dopaminergic projections drive sustained attention, working memory, motivation and the "get-up-and-go" that brain fog so conspicuously drains. As a 2020 Journal of Neuroscience study showed, brain iron tracks with cognition during development, and low brain-iron content is associated with poorer cognitive performance — mechanistically, low iron means less efficient dopamine synthesis and signalling. This is also why iron deficiency overlaps with the ADHD and dysautonomia literatures, and with restless legs, all of which involve dopaminergic and iron biology.

Myelin. Oligodendrocytes — the cells that wrap nerve fibres in myelin — have a high metabolic demand and depend on iron as a cofactor for lipid synthesis. Iron deficiency disrupts normal myelination, and white matter is the brain's wiring: when the insulation is thin, regions communicate more slowly, which shows up as reduced processing speed. This parallels the white-matter story in the B12 review and the vascular dementia review, where slow, poorly-myelinated wiring underlies the foggy, effortful quality of thinking.

BDNF and the hippocampus. Here is where iron deficiency converges most directly on Dihexa's pharmacology. In animal models, iron deficiency produces a long-term reduction of hippocampal BDNF, and it does so partly through chromatin remodelling at the Bdnf locus — repressive epigenetic marks that hold the gene down. Early-life iron deficiency also alters neurotrophic-factor expression and hippocampal neuron differentiation. BDNF binds the TrkB receptor and drives dendritic-spine maturation, long-term potentiation and memory consolidation; suppress it and synaptic plasticity falters.

This matters for two reasons. First, it explains why iron deficiency produces a genuine, mechanism-backed brain fog rather than an imagined one. Second, it pinpoints exactly where the convergence with Dihexa's pharmacology lies: the end-state of iron deficiency is reduced dopamine signalling, impaired myelination and suppressed BDNF-TrkB plasticity — the same downstream triad Dihexa's HGF/c-Met mechanism is claimed to support. We return to that overlap, and its limits, after the treatment evidence.

What the Treatment Evidence Shows: Iron Can Lift the Fog in the Right People

If low iron is doing the damage, can replacing it restore cognition? In adults — and unlike some early-life scenarios — the evidence is encouraging, and it is the strongest single argument against reaching for anything exotic.

A frequently cited randomised trial found that iron treatment "normalised" cognitive functioning in young women with iron deficiency, with the cognitive gains scaling with the improvement in iron status. More recently, a 2025 systematic review and meta-analysis of iron supplementation in non-anaemic children, adolescents and menstruating adults found benefits for cognitive and psychiatric outcomes — important because it speaks directly to the iron-deficient-but-not-anaemic group that standard testing misses. A study in older patients likewise found iron deficiency associated with cognitive impairment and improvement in cognitive scores after ferritin rose with treatment.

Where oral iron fails, is poorly tolerated or needs to work quickly, intravenous iron is increasingly used. The PREFER randomised, placebo-controlled study of single-dose intravenous ferric carboxymaltose in fatigued, iron-deficient women assessed fatigue, quality of life and cognitive function; and trials of intravenous iron for postpartum anaemia have targeted the fatigue and reduced cognitive ability that accompany it — the same territory as the postpartum brain fog review.

Early-Life vs Adult Iron Deficiency: Why Timing Changes the Story

The reversibility of iron-related cognitive symptoms depends heavily on when the deficiency happens, and this nuance is worth stating plainly because it is sometimes used to over-sell the case for "rescue" interventions.

In adults, correcting iron generally restores the dopamine, myelin-maintenance and neurotrophic systems, and cognition tends to recover with stores. In early life — fetal, neonatal and infant — the picture is different: iron deficiency during the brain's rapid building phase can produce persistent epigenetic suppression of BDNF and lasting neurocognitive effects that iron repletion alone only partly reverses. Studies of prenatal iron deficiency and choline supplementation show that some, but not all, of these marks can be mitigated — and that interventions which look helpful in deficiency can be unhelpful in iron-sufficient brains.

For the adult reading this with brain fog, the lesson is reassuring and pointed at once: your iron-related fog is likely to respond to correcting the iron, and the developmental data are an argument for prompt testing and treatment — not a reason to layer an unproven peptide on top of an unmeasured iron level. If anything, the early-life findings underline how specifically the brain needs iron at the right time, which is not something a synaptogenic compound provides.

Who Gets Iron Deficiency Brain Fog: The Risk Groups That Matter

Iron brain fog is not random. It clusters in identifiable groups, and recognising yourself in one of them is a far more useful step than any self-experiment.

Menstruating women and heavy periods

Monthly blood loss is the single biggest driver of iron deficiency in the UK, and heavy menstrual bleeding is a common, treatable cause that is frequently normalised by patients and clinicians alike. This is why iron deficiency is so much more common in women aged 18–50, and why the cognitive toll lands disproportionately on women. Investigating and managing heavy periods is part of the cure, not an afterthought.

Pregnancy and the postpartum period

Pregnancy roughly doubles iron requirements, and blood loss at delivery can tip women into postpartum iron deficiency or anaemia — a recognised contributor to the fatigue and "baby brain" covered in the pregnancy and postpartum review. Iron is one of the few clearly modifiable drivers of postpartum cognitive symptoms.

Coeliac disease and malabsorption

Unexplained iron deficiency is one of the classic presentations of coeliac disease, which impairs iron absorption in the small bowel — often alongside folate and B12, producing a genuinely multifactorial fog. Inflammatory bowel disease, atrophic gastritis and bariatric surgery similarly impair iron handling. This is why guidelines suggest coeliac testing in adults found to be iron-deficient without an obvious cause.

Vegetarian and vegan diets

Plant (non-haem) iron is less readily absorbed than the haem iron in meat, so people following vegetarian or vegan diets without attention to iron sources, vitamin-C pairing and absorption inhibitors (tea, coffee, calcium with meals) are at higher risk. This is among the most preventable causes — and it overlaps with the B12 risk discussed in the B12 review.

Gastrointestinal blood loss — the one that must be excluded

In men, and in women without an obvious gynaecological cause, an iron deficiency in an adult can be the first sign of slow bleeding from the gut — including ulcers, polyps and bowel cancer. This is the reason UK guidance triggers investigation of the gastrointestinal tract in many iron-deficient adults, and it is the single most important reason not to "treat" iron brain fog with anything that masks the symptom without finding the cause.

The reason this list matters to the Dihexa question is simple: each entry points to a specific, treatable (and sometimes urgent) action — manage heavy periods, treat coeliac disease, adjust the diet, investigate the gut. None of those actions is "take a synaptogenic peptide", and none of them is replaced by one.

The BDNF–HGF–c-Met Chain: Where Dihexa Enters the Picture

With the deficiency biology in place, the molecular overlap with Dihexa is easy to state — and easy to over-read. Iron deficiency converges on reduced hippocampal BDNF-TrkB signalling, impaired dopaminergic transmission and degraded myelination. Two of those — the BDNF endpoint and the white-matter/cerebrovascular support — are, point for point, systems Dihexa's mechanism is claimed to address.

Hippocampal BDNF binds the TrkB receptor and drives dendritic-spine maturation, LTP and memory consolidation. Independently, HGF/c-Met signalling drives synaptogenesis through the PI-3K/AKT and MAPK pathways — a parallel track to the same cellular outcome — and, unusually for a procognitive mechanism, it also supports cerebrovascular angiogenesis and blood-brain-barrier integrity. A 2021 Frontiers in Cell and Developmental Biology review details how MET expression in the cortex sustains adult synaptogenesis and angiogenesis.

Dihexa — a small peptide analogue derived from angiotensin IV — is a positive modulator of the HGF/c-Met pathway. Full detail is on the mechanism of action page; the foundational pharmacology is Benoist et al. (2014, JPET). Its relevance to iron brain fog rests on three points of overlap — and three matching caveats:

• Synaptogenesis as a parallel route to plasticity. When iron deficiency suppresses BDNF-TrkB signalling, a pathway that pushes synaptogenesis from a different axis is conceptually interesting. Caveat: the word is conceptually — there are no iron-deficiency data for Dihexa at all.
• Cerebrovascular and white-matter support. Iron deficiency impairs myelination and oxygen delivery; HGF/c-Met has a documented vascular and white-matter-relevant component. Caveat: mechanism is not evidence, and the iron that the brain actually needs is iron, not a peptide.
• The directionality problem is decisive. In iron deficiency the upstream driver — a missing mineral — is removable. Pushing synaptogenesis downstream while dopamine synthesis is throttled and myelin maintenance is starved is biologically back-to-front. The intervention that fixes the cause is iron, not a peptide layered on top of an unresolved deficiency.

This is the genuine mechanistic case for being curious about Dihexa here. The rest of the article is about why curiosity is not evidence — and why, in iron deficiency specifically, the existence of a cheap definitive treatment, plus the need to find the cause, makes the case for an unlicensed peptide weaker than almost anywhere else on this site.

Replacement First: The Only Evidence-Based Treatment

Any honest review of iron brain fog has to begin with iron replacement, because it is not merely first-line — it is the only treatment with an evidence base, and it is disease-modifying rather than cosmetic. Correcting iron restores tyrosine hydroxylase activity and dopamine synthesis, re-supplies oligodendrocytes for myelin maintenance, and (in animal models) lifts the epigenetic brake on hippocampal BDNF. Where absorption is intact, this means oral iron — commonly ferrous sulfate, ferrous fumarate or ferrous gluconate, increasingly given on alternate days to improve absorption and tolerability; where oral iron fails or is poorly tolerated, intravenous iron (ferric carboxymaltose or ferric derisomaltose) rebuilds stores quickly.

Several practical points follow, and they map closely onto the logic in the B12 review:

• Check ferritin with CRP. Ferritin is an acute-phase protein and rises with inflammation, so a "normal" ferritin in someone with active inflammation can hide depleted stores. Transferrin saturation helps when ferritin is ambiguous.
• Find out why. Replacement treats the deficiency; it does not explain it. Heavy periods, coeliac disease, diet and gastrointestinal blood loss each need their own follow-up — and in adults, excluding gut bleeding is not optional.
• Recovery takes time, and stores take longer. Symptoms often improve over weeks, but ferritin should be rebuilt to a comfortable level and treatment usually continues for months after haemoglobin normalises to refill stores — stopping too early invites relapse.
• Don't over-correct. The 2025 Oklahoma imaging data are reassuring about brain-iron safety at adequate systemic levels, but iron is not a "more is better" nutrient; the target is repletion, not loading.

Notice what is absent from that list: any role for a synaptogenic peptide. That is not an oversight — it is where the evidence sits.

When Brain Fog Persists Despite Iron Replacement

Some people continue to feel foggy after their iron is corrected, and this is the scenario in which the temptation to reach for something like Dihexa is strongest. Before any unlicensed compound, structured assessment is far more likely to find a treatable answer:

• Stores not actually rebuilt. A haemoglobin that has normalised does not mean ferritin is healthy. Re-checking ferritin and transferrin saturation confirms whether replacement has done its job, or whether ongoing loss is outpacing intake.
• Co-existing deficiencies. B12 and folate often travel with iron deficiency, especially in malabsorption; each independently causes brain fog and each needs correcting.
• A second diagnosis. Iron deficiency commonly coexists with thyroid disease, menopause, depression, anxiety and sleep disorders — any of which can independently sustain cognitive symptoms.
• Post-viral overlap. Iron handling is disturbed in inflammation, and serum ferritin during hospitalisation has been linked to brain fog after COVID-19; the Long COVID and ME/CFS reviews cover that fatigue-and-fog territory.
• The "low-normal" zone. Per the Oklahoma data, some people with replaced-but-still-low iron may remain functionally short; this is a conversation about optimising ferritin with a clinician, not about experimental chemistry.

The point is the same as ever: persistent iron brain fog almost always has a findable, treatable explanation that an unlicensed peptide would do nothing to address — and might obscure.

Iron-Specific Risks of Dihexa Use

Beyond the general safety considerations on the side effects page, iron deficiency raises specific concerns.

Masking a cause that can be serious. This is the central, and uniquely sharp, risk. In adults, iron deficiency is not merely a nutrient gap — it can be the first sign of gastrointestinal blood loss, including bowel cancer. Anything that produces a subjective lift — placebo included — while the deficiency goes uninvestigated is genuinely dangerous, because it can delay a diagnosis where time matters. In few conditions is masking this consequential.

Not addressing the deficiency at all. A peptide aimed at the downstream synapse does nothing for dopamine synthesis, myelin maintenance or oxygen delivery, all of which need iron. Taking it instead of checking ferritin is the same error as treating the surface while the cause continues underneath — just in a more expensive and unproven form.

The general c-Met / oncology caution. The standard Dihexa concern applies: c-Met activation is implicated in tumour growth and invasion across several cancers, so anyone with a personal or family history of c-Met-relevant cancers should not consider Dihexa for any indication — iron brain fog included. This caution is sharpened here by the fact that the deficiency itself may be pointing at an undiagnosed malignancy.

Unknown product quality and interactions. Unlicensed research chemicals carry no guarantee of composition, purity or labelling, and there are no pharmacokinetic data for Dihexa in anyone, let alone in a person with malabsorption or active blood loss.

The Fosgonimeton Parallel and the Limits of Mechanism

The most instructive cautionary tale for any HGF/c-Met-based cognitive claim is fosgonimeton (ATH-1017), Athira Pharma's HGF/MET positive modulator and the closest clinical-stage relative to Dihexa. Fosgonimeton was a genuine, injectable, clinically tested drug developed specifically to enhance HGF/c-Met signalling for cognition — exactly the mechanism Dihexa is promoted on. In 2024 it missed its primary endpoint in the Phase 3 LIFT-AD Alzheimer's trial.

The lesson is not that HGF/c-Met is irrelevant to cognition; it is that a coherent, well-funded, professionally executed attempt to turn that mechanism into clinical benefit failed its definitive test. If a purpose-built drug with proper trials could not convert the mechanism into measurable cognitive benefit in a defined population, the case for an unlicensed research chemical converting the same mechanism into benefit in iron brain fog — a condition that already has a cheap, definitive treatment and a mandatory cause-finding step — is weaker still. Mechanism-first reasoning is a hypothesis generator, not evidence.

Who Should Not Consider Dihexa for Iron Brain Fog

Bringing the threads together, Dihexa should not be considered by:

• Anyone who has not had ferritin (with CRP) and a full blood count checked — the blood test comes first, always.
• Anyone with confirmed iron deficiency who has not completed proper replacement and had the cause investigated (periods, coeliac, diet, and — crucially — the gastrointestinal tract where indicated).
• Anyone with rectal bleeding, change in bowel habit, weight loss, abdominal pain or other red-flag symptoms — these need urgent assessment, not a peptide trial.
• Anyone with a personal or family history of breast, ovarian, lung, gastric, bowel or other c-Met-relevant cancers.
• Anyone who is pregnant, breastfeeding or trying to conceive — iron status is critical in pregnancy, and Dihexa has no reproductive safety data.
• Anyone whose cognitive symptoms have not been distinguished from comorbid thyroid disease, menopause, depression or anxiety.

What the Evidence Actually Supports for Iron Brain Fog in 2026

Stripped to essentials, the evidence-based approach to iron brain fog is cheap, fast and effective:

• Test properly. Ferritin with CRP, plus a full blood count and transferrin saturation — don't be reassured by a "normal" haemoglobin if symptoms fit; ask about iron stores.
• Replace the iron. Oral iron (often alternate-day) where absorption is intact; intravenous iron where oral fails, is not tolerated, or needs to work fast. Continue long enough to refill stores, not just to fix the haemoglobin.
• Find and fix the cause. Heavy periods, coeliac disease, diet, and — in adults where indicated — investigation of the gastrointestinal tract.
• Recheck and don't over-correct. Re-measure ferritin; aim for repletion, not loading, given brain-iron safety considerations.
• Treat the comorbidity. Thyroid, menopause, mood, sleep and B12 each independently worsen cognition and each has evidence-based treatment.

What is absent from that list is any role for an unlicensed synaptogenic peptide — an honest reflection of where the evidence sits in 2026.

The Bottom Line in 2026

Iron deficiency brain fog is real, biological and unusually well understood. The NHS recognises the cognitive symptom; iron's role as a cofactor for dopamine synthesis and myelination explains how a missing mineral reaches the synapse, and animal work shows iron deficiency suppressing hippocampal BDNF; the 2025 meta-analysis shows replacing iron can help even non-anaemic adults; and the April 2025 Oklahoma study suggests the cognitive effects begin even at "below expected" but technically normal iron. The biology converges on reduced BDNF-TrkB plasticity and degraded myelin — the same downstream endpoint Dihexa's HGF/c-Met pharmacology reaches.

But iron deficiency is the condition where mechanism-first reasoning is at its very weakest, for two reasons: the upstream cause is a missing mineral you can simply replace, and the deficiency itself, in an adult, demands that you find out why — sometimes uncovering a problem far more important than the fog. Correcting iron restores dopamine and myelin and, caught early, lifts the fog — cheaply and definitively. The honest reading of the 2026 evidence is therefore: test first, replace second, find the cause third, treat comorbidity fourth, and research chemicals essentially last — if at all. With new data pushing toward measuring iron stores rather than waiting for anaemia, the momentum in this field is toward catching the deficiency sooner, not reaching past it for an unproven peptide. In a condition that can be the first sign of something serious, that distinction is not academic — it is the whole point.

Frequently Asked Questions

Related Reading on Dihexa.co.uk

• Dihexa for Vitamin D Deficiency Brain Fog (2026) — the third member of the nutritional-fog trilogy, with the 2026 midlife vitamin D–tau study.
• Dihexa for Vitamin B12 Deficiency Brain Fog (2026) — the other nutritional deficiency that travels with iron and shares the "normal but not optimal" problem.
• Dihexa for Magnesium Deficiency Brain Fog (2026) — the mineral shortfall that clusters with low iron and is just as easily missed on a routine blood test.
• Dihexa for Coeliac Disease & Gluten Brain Fog (2026) — a classic cause of unexplained iron deficiency through malabsorption.
• Dihexa for Menopause Brain Fog (2026) — the perimenopausal window where the 2025 Oklahoma iron study was set.
• Dihexa for Baby Brain, Pregnancy & Postpartum Brain Fog (2026) — iron is a leading modifiable driver of postpartum fog.
• Dihexa for ADHD (2026) — the iron-dopamine overlap that links iron status to attention.
• Dihexa for Long COVID Brain Fog (2026) — where ferritin and inflammation tangle with cognitive symptoms.
• Dihexa for ME/CFS (2026) — the fatigue-and-fog overlap where iron should always be checked.
• Dihexa for MCI & Brain Aging (2026) — the BDNF-TrkB endpoint iron brain fog shares.
• Dihexa vs BDNF: What "10 Million Times More Potent" Actually Means — in-depth look at the BDNF mechanism claim.
• Mechanism of Action — HGF/c-Met, PI-3K/AKT, dendritic spines, cerebrovascular angiogenesis.
• Side Effects & Risks — the general safety picture.
• UK Legal Status — where Dihexa sits in UK law and MHRA advertising rules.
• Fosgonimeton & Athira — the cautionary Phase 3 story.

External Authoritative Sources Cited

• University of Oklahoma / ScienceDaily (28 April 2025). Low iron could cause brain fog during the menopause transition.
• Cognitive Performance in Relation to Systemic and Brain Iron at Perimenopause (Nutrients, 2025; 17(5):745).
• University of Oklahoma news release — Low iron could cause brain fog during menopause transition, OU study suggests (2025).
• NHS — Iron deficiency anaemia overview (symptoms, causes, treatment).
• NICE Clinical Knowledge Summaries — Anaemia: iron deficiency.
• Ironically unwell: anaemia and iron deficiency among health-aware adults in the UK (2025).
• Iron deficiency, cognition, mental health and fatigue in women of childbearing age: a systematic review (Journal of Nutritional Science).
• Psychiatric and cognitive outcomes of iron supplementation in non-anaemic children, adolescents and menstruating adults: a meta-analysis and systematic review (Neuroscience & Biobehavioral Reviews, 2025).
• Iron treatment normalises cognitive functioning in young women (American Journal of Clinical Nutrition).
• Longitudinal development of brain iron is linked to cognition in youth (Journal of Neuroscience, 2020).
• Role of iron in brain development, aging, and neurodegenerative diseases (Annals of Medicine, 2025).
• Long-term reduction of hippocampal BDNF activity after fetal-neonatal iron deficiency in adult rats (Pediatric Research, 2009).
• Fetal iron deficiency induces chromatin remodelling at the Bdnf locus in adult rat hippocampus (2014).
• Early-life iron deficiency anaemia alters neurotrophic factor expression and hippocampal neuron differentiation in male rats.
• Prenatal iron deficiency and choline supplementation epigenetically regulate Jarid1b and Bdnf in the rat hippocampus (Nutrients, 2021).
• Iron deficiency without anaemia and reduced basal-ganglia iron content in youths (2025).
• Association between iron deficiency without anaemia and cognitive impairment in children (2025).
• Iron deficiency can cause cognitive impairment in geriatric patients.
• PREFER: single-dose intravenous ferric carboxymaltose in fatigued, iron-deficient women (randomised, placebo-controlled).
• Maternal fatigue after postpartum anaemia treatment with intravenous iron vs oral iron (randomised controlled trial).
• Serum ferritin level during hospitalisation is associated with brain fog after COVID-19.
• HGF and MET in brain development and neurological disorders (Frontiers in Cell and Developmental Biology, 2021).
• Benoist CC et al. (JPET, 2014). Dihexa procognitive effects via HGF/Met.