Can Dihexa treat OCD (obsessive-compulsive disorder)?

No. There is no clinical trial of Dihexa in any OCD or obsessive-compulsive spectrum population. Dihexa (PNB-0408) is an unscheduled research chemical with no approved human use for any condition. The mechanistic case is unusually interesting because Russo and Pietsch (2013, Biomarker Insights) found significantly decreased plasma hepatocyte growth factor (HGF) and gamma-aminobutyric acid (GABA) in individuals with OCD compared with neurotypical controls, with decreased urokinase plasminogen activator (uPA) and uPAR levels correlating with symptom severity. That is the single most direct biological link between the HGF/c-Met system Dihexa engages and OCD pathology. But there is a significant directionality concern: OCD is increasingly understood as a disorder of pathologically over-strengthened cortico-striato-thalamo-cortical (CSTC) loops in which the orbitofrontal cortex, anterior cingulate, ventromedial caudate and mediodorsal thalamus learn and consolidate compulsive behavioural sequences. A synaptogenic HGF/c-Met-activating peptide that augments BDNF/TrkB-dependent synaptic plasticity could plausibly reinforce rather than relieve these maladaptive learned loops — the same direction-of-effect problem that arises in tinnitus, in psychosis prodrome, and at the manic pole of bipolar disorder. Anyone with OCD in the UK should follow the NICE CG31 pathway via their GP — not self-experiment with research peptides.

What did the Russo 2013 paper actually find about HGF and GABA in OCD?

Anthony J. Russo and Stefanie C. Pietsch published 'Decreased Hepatocyte Growth Factor (HGF) and Gamma Aminobutyric Acid (GABA) in Individuals with Obsessive-Compulsive Disorder (OCD)' in Biomarker Insights in August 2013, examining plasma from 15 individuals with OCD and 17 neurotypical controls. They found: (1) significantly decreased plasma HGF in OCD versus controls; (2) significantly decreased plasma GABA in OCD versus controls, with low GABA correlating with high Y-BOCS symptom severity; (3) significantly decreased plasma urokinase plasminogen activator (uPA) and its receptor uPAR, with low uPA and uPAR correlating with high symptom severity; and (4) a biological link via the established literature that HGF directly modulates GABAergic interneuron migration and inhibition. This is the most direct mechanistic anchor connecting Dihexa's HGF/c-Met pharmacology to OCD pathology. The study is small (n=15 OCD, n=17 controls), single-centre, has not been replicated, and was published in a low-impact open-access journal — so the finding is hypothesis-generating, not definitive. But it sits inside a broader Russo programme that also documented decreased serum HGF in depression (2010), anxiety (2010), bipolar disorder (2010) and autism spectrum disorder (2014) — a remarkably consistent transdiagnostic HGF deficiency signal that the field has barely engaged with.

What happened to the Biohaven troriluzole Phase 3 OCD trial?

Biohaven's troriluzole (BHV-4157) is a third-generation glutamate-modulator prodrug of riluzole (the same molecule approved for ALS as Rilutek/Tiglutik). The OCD programme — targeting glutamatergic dysregulation in the cortico-striato-thalamo-cortical circuit — comprised two pivotal Phase 3 studies (NCT04693351 and NCT04641143, the so-called PROUDD-1 and PROUDD-2 trials) of troriluzole as adjunctive therapy on top of an SSRI in adults with OCD who had failed standard treatment. Topline data from the two studies were expected in the first and second half of 2025 respectively. The trials read out negative: in mid-to-late 2025, Biohaven disclosed that the OCD Phase 3 programme did not detect an efficacy signal versus placebo on the primary Y-BOCS endpoint. The OCD indication has effectively been discontinued. (Troriluzole received a separate FDA PDUFA decision for spinocerebellar ataxia (SCA) in Q4 2025 on the back of the HOPE-1/2/3 programme.) The pattern is important context for OCD: even a sophisticated glutamate-modulator built on decades of riluzole-augmentation literature failed to clear Phase 3 efficacy in OCD. It tightens the priors against any unproven peptide claim.

What is the current UK NHS treatment pathway for OCD in 2026?

The current pathway is anchored by NICE CG31 (November 2005), 'Obsessive-compulsive disorder and body dysmorphic disorder: treatment'. NICE plans to consult on a first batch of guideline updates in autumn 2026, but CG31 remains the active reference. Treatment is stratified by functional impairment severity: mild impairment — low-intensity CBT including Exposure and Response Prevention (ERP), up to 10 therapist hours, often via NHS Talking Therapies (the renamed IAPT service); moderate impairment — choice of SSRI or more intensive CBT/ERP (>10 therapist hours); severe impairment — combined SSRI and intensive CBT/ERP. NICE-recommended SSRIs are fluoxetine, sertraline, fluvoxamine, paroxetine, escitalopram and citalopram, typically at higher doses than for depression and titrated to BNF maximum. Clomipramine (a serotonergic tricyclic) is the licensed alternative for SSRI non-response. If adequate response (a 25-35% Y-BOCS reduction) is not achieved within 12 weeks of an SSRI alone or after >10 therapist hours of CBT alone, a multidisciplinary review and consideration of treatment-resistant pathway options follows: SSRI augmentation with low-dose antipsychotics (risperidone, aripiprazole, quetiapine), specialist tertiary referral, and for the most refractory minority, consideration of deep brain stimulation, deep TMS or ablative neurosurgery in a tertiary national service. Waiting times for NHS Talking Therapies ERP vary considerably by region; OCD-UK and OCD Action maintain helplines for navigating access.

Is psilocybin or DBS being approved for OCD in the UK?

Psilocybin: not yet approved for OCD. The Compass Pathways COMP360 25mg synthetic psilocybin programme has reported two positive Phase 3 trials in treatment-resistant depression (COMP005 in 2025, COMP006 in 2026), but no Phase 3 OCD readout exists. Yale's OCD Research Clinic (Pittenger group) is running a randomised, double-blind, placebo-controlled, non-crossover single-dose psilocybin OCD study and a separate repeated-dosing study. Initial Phase 1/2 data from Yale and University Hospitals Cleveland Medical Center have suggested rapid Y-BOCS reductions in small open-label cohorts, but a Phase 3 OCD programme has not been initiated as of May 2026. DBS: deep brain stimulation of the ventral capsule / ventral striatum (VC/VS) has held an FDA Humanitarian Device Exemption since 2009 for refractory OCD, and the Medtronic Reclaim system is the available device. In the UK, DBS for refractory OCD is delivered in a small number of NHS tertiary centres (Cambridge, Oxford, Bristol, Frenchay) on a highly selected patient basis — typically after failure of multiple SSRIs, clomipramine, augmentation, and intensive specialist CBT, with Y-BOCS scores typically >30. The 2021 Cambridge BNST (bed nucleus of the stria terminalis) trial reported sustained responder status at 15-month endpoint. BrainsWay deep TMS using the H7 coil received FDA approval in 2018 and NICE IPG 2021 covered it; it is available in private clinics in the UK but variable NHS availability.

What is the theoretical risk that Dihexa could make OCD worse rather than better?

This is the central concern. OCD is increasingly understood as a disorder of pathologically over-strengthened cortico-striato-thalamo-cortical (CSTC) loops — the orbitofrontal cortex, anterior cingulate, ventromedial caudate, and mediodorsal thalamus learn and consolidate compulsive behavioural sequences that resist extinction. The 2025 Gonzalez Journal of Neurochemistry review framed Crym-positive striatal astrocytes as gatekeepers of perseverative behaviour through their effects on cortico-striatal presynaptic terminals. SAPAP3-knockout and SLITRK5-knockout mice show compulsive grooming driven by exactly this circuit. The therapeutic logic of effective OCD treatments (high-dose SSRIs, ERP, ablative cingulotomy, VC/VS DBS) is to weaken or disrupt this maladaptive cortico-striatal loop. A synaptogenic HGF/c-Met-activating peptide that augments BDNF/TrkB-dependent dendritic spine formation and synaptic strengthening could, in principle, consolidate rather than weaken these learned loops — the OCD analogue of the central-gain risk in tinnitus, the prodromal-psychosis risk in schizophrenia, and the manic-switch risk in bipolar disorder. Russo's finding of decreased plasma HGF in OCD could be read either as 'low HGF is part of the OCD problem' or 'low HGF is the brain's protective downregulation against further consolidation' — and we genuinely don't know which. This is why mechanistic plausibility is necessary but not sufficient evidence for a clinical claim.

OCD & Anxiety Spectrum Published: 23 May 2026 · 32 min read

Dihexa for OCD (Obsessive-Compulsive Disorder): HGF/GABA Russo 2013, BDNF, Cortico-Striatal Circuit, Troriluzole BHV-4157, Psilocybin COMP360 & the 2026 UK Review

Around 750,000 UK adults — roughly 1.2% of the population at any point in time — live with obsessive-compulsive disorder (OCD), with a 1-2% lifetime prevalence rising to 2-3% under broader case definitions, on Priory 2026 statistics consistent with OCD-UK figures. 2025-2026 has been a turbulent period in the field. In August 2013, Russo and Pietsch published in Biomarker Insights the only paper in the literature directly linking decreased plasma hepatocyte growth factor (HGF) and GABA to obsessive-compulsive disorder — an unusually direct biological anchor for the HGF/c-Met axis that Dihexa engages. In 2025 the Gonzalez group’s Journal of Neurochemistry review reframed OCD as an astrocyte disorder, identifying Crym-positive striatal astrocytes as gatekeepers of perseverative behaviour through cortico-striatal presynaptic regulation, and Zhu and colleagues’ Psychiatry & Clinical Neurosciences 1H-MRS meta-analysis consolidated decreased striatal N-acetylaspartate and elevated thalamic choline as the neurometabolic signature of OCD. The 2025 Frontiers in Psychiatry striatal-subregion functional-connectivity paper mapped the static and dynamic abnormalities to ventromedial vs dorsolateral caudate territory. In September 2025, Biohaven’s troriluzole (BHV-4157) — the most-watched glutamate-modulator adjunctive therapy in OCD — read out negative across both Phase 3 PROUDD pivotal trials with no efficacy signal. The Yale OCD Research Clinic (Pittenger group) progressed its randomised, double-blind, placebo-controlled, non-crossover single-dose psilocybin OCD protocol — the first rigorous test of a psychedelic in OCD. NICE has confirmed an autumn 2026 consultation on updates to CG31 (November 2005). Against this backdrop, does Dihexa, the synaptogenic HGF/c-Met-activating peptide, have anything to offer the UK’s 750,000 OCD sufferers — and is there a real theoretical risk that more cortico-striatal synaptic plasticity could consolidate rather than weaken the maladaptive loop? This rigorous 2026 UK review covers what is actually known, what is speculation, and where the evidence is genuinely absent. Readers may also want to read the closely related Dihexa for Anxiety & Chronic Stress review (the dominant OCD comorbidity), the Dihexa for Depression & Mood review (50-60% lifetime co-occurrence), the Dihexa for ADHD review (high paediatric OCD comorbidity), the Dihexa for Bipolar Disorder review (sister Russo HGF paper) and the Dihexa for PTSD review (the broader anxiety-disorders OCD comorbidity).

Not Medical Advice. Dihexa (PNB-0408) is an unscheduled research chemical with no approved human use for any condition, including obsessive-compulsive disorder. Nothing on this page is medical advice. The evidence-based 2026 UK pathway for OCD is GP-led assessment and referral under NICE CG31 to NHS Talking Therapies for Exposure and Response Prevention (ERP), an SSRI titrated to BNF maximum, and tertiary specialist referral if treatment-resistant. Anyone with OCD — especially with comorbid depression, suicidal thinking, hoarding presenting safety risk, or paediatric/perinatal onset — should be assessed clinically rather than self-experiment with research peptides. If you are in crisis, call Samaritans on 116 123 (free, 24/7) or contact NHS 111. Read the full legal disclaimer.

Key Findings: Dihexa & OCD (Obsessive-Compulsive Disorder)

Human evidence in OCD: None. Zero clinical trials of Dihexa in OCD or any obsessive-compulsive spectrum disorder.
UK scale: ~750,000 UK adults; ~1.2% point prevalence, 1-2% lifetime (OCD-UK, Priory 2026).
The mechanistic anchor: Russo & Pietsch (2013, Biomarker Insights) documented significantly decreased plasma HGF, GABA, uPA and uPAR in OCD versus controls — the single most direct biological link between Dihexa’s HGF/c-Met pharmacology and OCD pathology.
2025 astrocyte reframe: Gonzalez et al. (2025, J Neurochem) identified Crym-positive striatal astrocytes as gatekeepers of perseverative behaviour through cortico-striatal presynaptic regulation.
2025 neurometabolic signature: Zhu et al. (2025) 1H-MRS meta-analysis — decreased striatal NAA, elevated thalamic choline.
2025 troriluzole failure: Biohaven’s BHV-4157 Phase 3 PROUDD-1/PROUDD-2 trials in adjunctive OCD-on-SSRI failed with no efficacy signal — tightening the priors against any unproven OCD therapy claim.
2025 psilocybin signal: Yale OCD Research Clinic single-dose psilocybin RCT protocol active; Compass COMP360 Phase 3 success in TRD does not translate to OCD evidence yet.
UK guideline: NICE CG31 (Nov 2005) with autumn 2026 update consultation; SSRI + ERP first-line, clomipramine second-line, antipsychotic augmentation third-line, DBS / deep TMS / ablative neurosurgery for the refractory tail.
Clinical cousin: Fosgonimeton (ATH-1017) — the closest HGF-pathway molecule with human data — has never been tested in any OCD population.
Theoretical directionality risk: OCD’s pathology is pathologically over-strengthened CSTC loops; a synaptogenic peptide could plausibly consolidate rather than weaken them — the OCD analogue of the central-gain problem in tinnitus.
Bottom line: The Russo 2013 HGF/GABA finding is one of the most direct biological links to Dihexa biology of any psychiatric condition — yet completely untested clinically, with a real theoretical risk of CSTC consolidation. Cannot be recommended for OCD in 2026.

OCD in the UK in 2026: Scale, Definitions & Why It Matters

Obsessive-compulsive disorder (OCD) is one of the most common, most disabling, and most under-treated chronic psychiatric conditions in adult medicine. The Priory 2026 OCD statistics report and OCD-UK aligned figure put the UK adult point prevalence at roughly 1.2% (around 750,000 adults living with diagnosed OCD), with a lifetime prevalence of 1-2% on conservative case definitions and as high as 2-3% under broader criteria. The World Health Organization has consistently ranked OCD among the top 10 most disabling medical conditions worldwide on years-lived-with-disability metrics, comparable to chronic schizophrenia. The average diagnostic delay from symptom onset to first effective treatment in the UK is still measured in years — often a decade or more.

The diagnostic framework recognised in NICE CG31 (November 2005) — aligned with DSM-5 and ICD-11 — defines OCD by the co-occurrence of obsessions (recurrent, intrusive, ego-dystonic thoughts, images, urges or doubts — the dominant content domains are contamination, harm, symmetry/“just right”, sexual, religious/scrupulosity, and relationship ROCD themes) and compulsions (repetitive overt or mental acts the person feels driven to perform to reduce distress or prevent a feared outcome; in “Pure O” purely obsessional OCD the compulsions are predominantly covert mental acts). The Yale-Brown Obsessive Compulsive Scale (Y-BOCS) — 0-40 score — remains the gold-standard severity measure: 0-7 subclinical, 8-15 mild, 16-23 moderate, 24-31 severe, 32-40 extreme.

The obsessive-compulsive and related disorders chapter in DSM-5 includes body dysmorphic disorder (BDD; covered alongside OCD in NICE CG31), hoarding disorder, trichotillomania, excoriation (skin-picking) disorder, and substance/medication-induced OCD. Demographics: OCD shows a bimodal age of onset — early peak at ages 10-12 (often male-predominant, more tic-related) and adult peak at 19-25 (more female-predominant); approximately 50% of cases present before age 18. Heritability is consistently 40-65% in twin studies, with leading candidate gene contributions from SLC1A1 (EAAT3 glutamate transporter), GRIN2B, SLITRK5, SAPAP3 and the BDNF Val66Met polymorphism.

Comorbidity is the rule. Approximately 60-65% have lifetime major depressive disorder, 30-50% have a comorbid anxiety disorder, ~20% of adults have comorbid ADHD, ~17% have comorbid autism spectrum disorder, ~10-15% have bipolar disorder, and 12-25% of OCD patients have a schizophrenia-spectrum comorbidity (so-called “schizo-obsessive” presentation). Paediatric OCD has substantial tic and Tourette syndrome overlap, including the PANDAS / PANS post-infectious autoimmune subset. The OCD suicide-risk relative is approximately 5-10 times general-population baseline, with lifetime ideation ~30% and lifetime attempt ~10%.

The three UK numbers that matter. ~750,000 UK adults live with diagnosed OCD; 1-2% lifetime prevalence; average diagnostic delay still measured in years. There is no NICE-recommended peptide for OCD in 2026 — the entire evidence base is high-dose SSRIs, intensive ERP-based CBT, clomipramine, antipsychotic augmentation, and for the refractory tail, DBS, deep TMS, or ablative neurosurgery in tertiary national services.

The Modern Mechanistic Picture: CSTC Loop, Glutamate, GABA, BDNF & the HGF Anchor

The dominant explanatory framework for OCD in 2026 is pathological over-strengthening of cortico-striato-thalamo-cortical (CSTC) loops, layered on top of glutamatergic dysregulation, GABAergic interneuron dysfunction, recently-recognised astrocyte involvement, and an emerging serotonergic / neurotrophic story in which BDNF and HGF play structural roles.

The CSTC Circuit

Decades of neuroimaging, lesion data, primate physiology, mouse-genetic models and human DBS evidence converge on a single anatomical loop: orbitofrontal cortex (OFC) → ventromedial caudate / ventral striatum → globus pallidus internus / substantia nigra pars reticulata → mediodorsal thalamus → cortical re-entry to OFC and anterior cingulate. The standard model is that reduced inhibitory tone at the striatal level allows the loop to enter pathological positive feedback: an obsession triggers a compulsion, the compulsion transiently relieves distress, and the relief negatively reinforces the entire loop, consolidating the cortico-striatal synaptic strengths. The Vaghi CSTC working-memory framework and the 2025 “Rewiring the OCD brain” review survey the modern circuit-level evidence. The 2025 Frontiers in Psychiatry static and dynamic functional-connectivity paper showed OCD patients have abnormal ventromedial-caudate-to-OFC and dorsolateral-caudate-to-DLPFC connectivity; the default mode network never properly deactivates.

Glutamatergic Dysregulation

The single most important pharmacological insight of the last 20 years in OCD is that glutamatergic dysregulation in cortico-striatal pathways is at least as central as serotonergic dysfunction. The Zhu 2025 1H-MRS meta-analysis showed decreased striatal N-acetylaspartate and elevated thalamic choline, with Y-BOCS severity correlating with striatal choline. CSF glutamate is elevated in adult OCD; SLC1A1 (EAAT3) and GRIN2B are among the most replicated genetic signals. Glutamate-targeting molecules — riluzole, memantine, N-acetylcysteine, lamotrigine, ketamine — have all shown small-trial signals; the 2025 Biohaven troriluzole Phase 3 failure (below) is the most informative recent test. The Gonzalez 2025 Journal of Neurochemistry review reframed OCD as an astrocyte disorder, with Crym-positive striatal astrocytes directly gating cortico-striatal presynaptic glutamate release.

GABAergic Inhibition Deficit

Excitatory glutamatergic over-drive in OCD is mirrored by a GABAergic inhibitory deficit — particularly in striatal parvalbumin-expressing fast-spiking interneurons. The Russo & Pietsch 2013 paper documented decreased plasma GABA in OCD versus controls, with low GABA correlating with high Y-BOCS severity. HGF is one of the most important positive regulators of GABAergic interneuron migration, maturation and inhibitory function in the developing and adult brain — the same interneuron population whose dysfunction is implicated in OCD CSTC over-activity. This is the deepest mechanistic link between Dihexa biology and OCD pathology.

BDNF & Synaptic Plasticity

The Mansueto 2024 Journal of Affective Disorders paper showed that in OCD responders to combined SSRI + CBT, serum BDNF increases correlated with cognitive recovery on executive-function and processing-speed measures. The 2022 BDNF Alleviates Microglial Inhibition and Stereotypic Behaviours paper showed targeted BDNF delivery reversed stereotypic perseverative behaviours in a mouse OCD model — suggesting BDNF augmentation might reduce rather than reinforce compulsions. The May 2025 BDNF Transformative Target review and 2025 Science Advances autocrine MMP-9 paper consolidate BDNF as a foundational target.

HGF/c-Met — The Most Direct Mechanistic Anchor in Psychiatry

The Russo & Pietsch 2013 paper in Biomarker Insights is the single most important Dihexa-relevant finding in the OCD literature. In a study of 15 individuals with OCD versus 17 neurotypical controls, the authors documented significantly decreased plasma hepatocyte growth factor (HGF), GABA (low GABA correlating with high Y-BOCS), urokinase plasminogen activator (uPA; low uPA correlating with Y-BOCS), and uPAR. The biological framing: HGF is a master regulator of GABAergic interneuron function, and reduced HGF/uPA/uPAR signalling would drive reduced cortical and striatal GABAergic inhibition. Caveats: the study is small, single-centre, unreplicated. But it sits inside a strikingly consistent Russo programme that has documented decreased serum HGF in depression (2010), anxiety (2010), bipolar disorder (2010; see our bipolar review), and autism spectrum disorder (2014). The Benoist 2014 JPET paper established Dihexa's HGF/c-Met dependence; Wright & Harding 2015 reviewed the brain HGF/c-Met system as therapeutic target.

The 2026 UK Treatment Landscape: NICE CG31, SSRIs, ERP, Clomipramine & Augmentation

UK OCD management is anchored by NICE CG31 (November 2005), with an autumn 2026 consultation on updates confirmed. Treatment is stratified by impairment severity:

Mild impairment: Low-intensity CBT with ERP (up to 10 therapist hours) via NHS Talking Therapies (formerly IAPT).
Moderate impairment: Choice of SSRI (fluoxetine, sertraline, fluvoxamine, paroxetine, escitalopram or citalopram, titrated to BNF maximum, ≥12 weeks) or intensive CBT/ERP (>10 hours).
Severe impairment: Combined SSRI + intensive ERP-based CBT first-line.

~One-third fail first-line. Escalation: switch SSRI; clomipramine (TCA, requires ECG/plasma monitoring); SSRI + clomipramine combination; low-dose antipsychotic augmentation (risperidone, aripiprazole, quetiapine); specialist tertiary referral (South London & Maudsley Anxiety Disorders Residential Unit, Bethlem; Oxford Health OXTOP; Springfield Hospital London; tertiary services in Cambridge/Oxford/Bristol).

Adjunctive & Off-Label Pharmacology — The Glutamate Stack

None NICE-recommended, all specialist-prescribed: NAC 2400-3000mg (BFRBs), memantine 10-20mg, riluzole (parent of troriluzole), lamotrigine, topiramate, pregabalin, ondansetron, agomelatine, inositol (Sayyah double-blind), CBD. IV ketamine produces rapid short-lived Y-BOCS reductions; aversive dissociative experience limits utility.

Refractory Interventions: DBS, Deep TMS & Ablative Neurosurgery

For the refractory minority (Y-BOCS >30; failure of multiple SSRIs, clomipramine, augmentation and intensive CBT): VC/VS DBS — FDA Humanitarian Device Exemption since 2009, Medtronic Reclaim system; international multicentre cohorts ~60% Y-BOCS responder rate. UK DBS available in Cambridge/Oxford/Bristol/Frenchay. The 2021 Cambridge BNST trial reported all participants achieved responder status at 15 months. STN DBS from the 2008 Mallet NEJM French trial. BrainsWay deep TMS H7 coil FDA-approved 2018; NICE IPG 709 (2021) covered. Bilateral capsulotomy, anterior cingulotomy and MRgFUS focused ultrasound retain a refractory-tail niche.

The 2026 OCD Drug-Development Landscape: Troriluzole Failure & Psilocybin Promise

Biohaven Troriluzole (BHV-4157) Phase 3 PROUDD Failure (September 2025)

Troriluzole (BHV-4157) is a third-generation prodrug of riluzole. The OCD programme built on a decade of open-label data from Christopher Pittenger's group at Yale. Biohaven's two pivotal Phase 3 placebo-controlled studies of troriluzole 200mg adjunctive on SSRI — NCT04693351 (PROUDD-1) and NCT04641143 (PROUDD-2) with the NCT04708834 long-term safety extension — were expected to read out in 1H 2025 and 2H 2025. They read out negative: no efficacy signal on the primary Y-BOCS endpoint. Biohaven disclosed the failure in mid-to-late 2025 and the OCD indication has effectively been discontinued. Troriluzole received a separate FDA PDUFA decision for spinocerebellar ataxia (SCA) in Q4 2025. The PROUDD result is informative: even a sophisticated, biology-anchored glutamate-modulator with 20 years of supporting literature failed Phase 3 in OCD — tightening the priors against any unproven mechanism claim.

Psilocybin: Compass COMP360 in TRD, Yale OCD Research Clinic in OCD

Compass Pathways reported two positive Phase 3 trials of COMP360 25mg synthetic psilocybin in treatment-resistant depression: COMP005 (2025; 258 patients; MADRS −3.6, p<0.001) and COMP006 (2026; two fixed doses 3 weeks apart; MADRS −3.8, p<0.001). No Phase 3 OCD readout exists yet. The principal active OCD work is the Yale OCD Research Clinic single-dose psilocybin RCT and a separate repeated-dosing study. Earlier Phase 1/2 work by Moreno (2006) and Wilcox (2014) showed rapid Y-BOCS reductions in small open-label cohorts.

Where Could Dihexa Theoretically Fit in OCD Biology?

OCD pathology axis	Dihexa mechanistic rationale	Strength of case
HGF/uPA/uPAR deficiency (Russo 2013)	Dihexa is a positive allosteric modulator of HGF/c-Met; directly addresses the documented deficiency.	Strongest in psychiatry. Most direct link of any psychiatric condition; single unreplicated study.
GABAergic inhibition deficit	HGF/c-Met regulates parvalbumin-interneuron migration / maturation.	Plausible. Strong developmental literature.
CSTC loop over-strengthening	Dihexa augments BDNF/TrkB synaptogenesis — the machinery consolidating the maladaptive loop.	Concerning. Could consolidate rather than weaken.
BDNF cognitive recovery (Mansueto 2024)	Could support cognitive recovery in effective OCD treatment; possible ERP augmentation.	Weak-to-moderate. Adjunct only.
Astrocyte dysfunction (Gonzalez 2025)	HGF regulates astrocyte function and glutamate-transporter expression.	Weak. No direct data.

The honest summary: the biological case is more direct than for most psychiatric conditions, but is contradicted by a serious directionality concern. OCD is, fundamentally, a disorder of too much cortico-striatal synaptic plasticity in the wrong place. The therapeutic logic of every effective OCD intervention is fundamentally disruptive rather than synaptogenic. A peptide whose primary action is to build new synapses in the same circuit is at minimum a directional gamble.

The One Plausible Frame: ERP Augmentation Through Extinction-Learning Consolidation

The strongest theoretical case for a synaptogenic peptide in OCD is not as standalone treatment but as ERP augmentation — using the peptide to consolidate the extinction learning that ERP induces, by analogy with the d-cycloserine ERP-augmentation literature. The peptide would be dosed acutely around an intensive ERP session to strengthen new safety-learning. This is the most defensible mechanistic frame for a hypothetical future Dihexa OCD trial. It remains entirely hypothetical: no preclinical Dihexa-plus-extinction-learning model, no Phase 1 work in any anxiety-spectrum population. Fosgonimeton (ATH-1017), the closest HGF-pathway molecule with human data, has never been tested in any anxiety or OCD indication.

Risks & Theoretical Concerns Specific to OCD

Beyond the generic risks in the Dihexa side-effects review, OCD-specific concerns include: CSTC consolidation (core directionality risk); pro-anxiety pharmacodynamics (BDNF augmentation has anxiogenic signals in some preclinical models — see Anxiety review); manic switch in comorbid bipolar (~10-15% OCD-bipolar comorbidity — see Bipolar review); prodromal psychosis risk in schizo-obsessive presentations (see Schizophrenia review); paediatric onset (~50% of cases begin before age 18; no paediatric Dihexa data; HGF/c-Met developmentally critical — off-label paediatric use contraindicated); SSRI / clomipramine drug-drug interactions (serotonin-syndrome risk in clomipramine + SSRI already real); c-Met oncogenicity (chronic c-Met activation concern, particularly given the younger OCD demographic and potential decades-long exposure).

UK Resources, Charities & Specialist Services for OCD

National charities: OCD-UK (Ashley Fulwood); OCD Action; International OCD Foundation (IOCDF); BDD Foundation; Mind; Rethink Mental Illness; Samaritans 116 123.

NHS pathway: GP referral to NHS Talking Therapies (self-referral available) for ERP-based CBT; tertiary referral to South London & Maudsley Anxiety Disorders Residential Unit (Bethlem), Oxford Health OXTOP; refractory DBS via Cambridge/Oxford/Bristol/Frenchay tertiary neurosurgery.

Research & professional bodies: NIHR Be Part of Research for open OCD trials; MQ Mental Health Research; BABCP (CBT therapist register — use “Find a Therapist”); Royal College of Psychiatrists CR152.

The 2026 Bottom Line

OCD is one of the most mechanistically interesting psychiatric conditions for the HGF/c-Met axis — and one of the most theoretically risky. The Russo & Pietsch 2013 paper provides the most direct biological link between Dihexa's pharmacology and any psychiatric condition. The 2025 astrocyte / striatal-connectivity / 1H-MRS reframe sharpens the underlying neurobiology. The 2024 Mansueto BDNF cognitive-recovery finding offers a coherent neurotrophic story for treatment response. But OCD is the condition where the direction-of-effect problem is most pointed. Every effective OCD treatment weakens or disrupts a pathologically over-strengthened cortico-striato-thalamo-cortical loop. The 2025 Biohaven troriluzole Phase 3 PROUDD failure tightens the priors against any unproven mechanism claim. No clinical trial of Dihexa in any OCD population has been conducted, registered, or planned. The evidence-based 2026 UK pathway is GP referral to NHS Talking Therapies for ERP-based CBT, SSRI titrated to BNF maximum, and tertiary specialist referral if treatment-resistant. OCD-UK and OCD Action are the principal navigation resources. The Russo 2013 finding deserves replication and proper preclinical development — not premature self-experimentation.

Selected References & External Sources

Russo AJ, Pietsch SC (2013). Decreased HGF and GABA in OCD. Biomarker Insights. — PMC3762604 · SAGE · PubMed 24023510
Gonzalez et al. (2025). Astrocyte Dysfunctions in OCD. J Neurochem. — Wiley · PMC12095986
Zhu et al. (2025). 1H-MRS meta-analysis in OCD. Psychiatry Clin Neurosci. — Wiley
Wang et al. (2025). Striatal subregion functional connectivity in OCD. Front Psychiatry. — Frontiers
Mansueto et al. (2024). BDNF in acute OCD treatment. J Affect Disord. — ScienceDirect
NICE CG31 (Nov 2005). OCD and BDD treatment. — nice.org.uk/guidance/cg31
BDNF stereotypic behaviour OCD mouse (2022). — PMC9325681
Pittenger psilocybin OCD protocol (2023). — PMC10166878 · Yale OCD Research Clinic
Biohaven Troriluzole Phase 3 OCD: NCT04693351 · NCT04641143 · NCT04708834 · SEC EDGAR
Compass COMP360 in TRD. — compasspathways.com · COMP006
Priory (2026). UK OCD statistics. — priorygroup.com
OCD-UK. — ocduk.org · OCD Action. — ocdaction.org.uk · IOCDF. — iocdf.org
Cambridge BNST DBS (2021). — Cambridge · PMC8007749
VC/VS DBS multicentre. — PMC7985042
NICE IPG 709 (2021) Deep TMS for OCD. — nice.org.uk/guidance/ipg709
BDNF Transformative Target (2025). — PMC12071950 · BDNF MMP-9 (2025). — Science Advances
Russo HGF transdiagnostic series: depression 2010 · anxiety 2010 · ASD 2014
Benoist et al. (2014). HGF/c-Met dependence of Dihexa. JPET. — PubMed 24403718 · Wright & Harding (2015). Brain HGF/c-Met. — PubMed 25711386
NHS Talking Therapies. — nhs.uk/talking-therapies · BABCP. — babcp.com · RCPsych. — rcpsych.ac.uk
Vaghi CSTC WM OCD. — PMC4854867 · Rewiring the OCD brain (2025). — ScienceDirect