Takeaway & Abstract
One-sentence takeaway: In a 2026 rat model of Fragile X, repeated low doses of psilocybin improved object-recognition memory through a TrkB-dependent pathway without requiring 5-HT2A activation; Xycota is preparing a 28-day study in adults with mild PTSD to test whether low-dose psilocybin changes human PTSD symptoms. Post-traumatic stress disorder (PTSD) is associated with dendritic spine loss and reduced synaptic connectivity in the medial prefrontal cortex (mPFC) and hippocampus (Peters et al., Science 2010). Preclinical pharmacology indicates that TrkB-dependent plasticity effects in animals can be separated from 5-HT2A-driven behavioral effects (Moliner et al., Nat Neurosci 2023; Ascone et al., Neuropsychopharmacology 2026). Those animal findings motivate Xycota's investigational lead candidate, XYCO-02 (sub-perceptual oral psilocybin capsule), for which a Canadian Clinical Trial Application is in preparation. XYCO-02 is preclinical and not approved, and human clinical benefit has not yet been demonstrated.
Chronic stress and traumatic exposure are associated with reduced neurotrophin signaling, disrupted glutamate homeostasis, and retraction of dendritic spines in the hippocampus and prefrontal cortex. In preclinical fear-extinction models, exogenous Brain-Derived Neurotrophic Factor (BDNF) infusion in the hippocampal-infralimbic medial prefrontal circuit is sufficient to induce fear extinction even without extinction training (Peters et al., Science 2010).
When dendritic arborization is compromised, top-down prefrontal inhibition of the amygdala weakens. A central research question is whether supporting BDNF and Tropomyosin receptor kinase B (TrkB) signaling can help restore synaptic connectivity in trauma-related circuits.
Historically, psychedelic research assumed that neuroplastic effects required high-dose, perception-altering sessions driven by 5-HT2A receptor agonism. Recent preclinical receptor studies have tested whether those pathways can be separated in animals.
In a 2023 study in Nature Neuroscience, Moliner and colleagues reported that psilocin and LSD bind directly to TrkB as allosteric modulators of endogenous BDNF signaling (Moliner et al., 2023). In their animal models, effects on plasticity depended on TrkB binding and endogenous BDNF signaling rather than 5-HT2A activation, whereas the head-twitch response depended on 5-HT2A.
Xycota's hypothesis: The animal finding gives Xycota a reason to investigate low-dose psilocybin in people. The clinical question is whether people with mild PTSD experience a change in symptoms when taking a sub-perceptual dose formulated to minimize noticeable psychedelic effects.
One of the central methodological challenges in high-dose psychedelic trials is functional unblinding. In published trials of perceptible doses (such as 25 mg of psilocybin), over 90% of participants or raters correctly identify treatment assignment (Muthukumaraswamy et al., Expert Rev Clin Pharmacol 2021), and each 25 mg administration requires a supervised clinic session lasting 6 to 8 hours (Goodwin et al., NEJM 2022).
| Published macrodose protocols (25 mg) | Planned XYCO-02 study (sub-perceptual) |
|---|---|
| Functional unblinding exceeding 90% in published trials (Muthukumaraswamy et al., 2021) | Dosing goal: Minimize perceptual effects; repeated-dose blinding in mild PTSD remains an open question |
| 25 mg in a supervised clinic session lasting 6 to 8 hours (Goodwin et al., 2022) | Planned study: 28 days, at-home oral dosing |
| Acute perceptual and subjective effects expected during dosing | Sub-perceptual dose formulated to reduce the risk that noticeable effects reveal treatment assignment |
| In-clinic supervision required during each dosing session | Planned study design: Double-blind outpatient protocol |
What "sub-perceptual" means: Sub-perceptual describes the design goal for XYCO-02. The low-dose oral regimen is formulated to stay below the threshold of noticeable psychedelic effects. Blinded single-dose research in healthy adults has evaluated low-dose oral psilocybin to characterize perceptual thresholds relative to placebo (read the single-dose study in healthy adults). Whether participants with mild PTSD can distinguish XYCO-02 from placebo during repeated dosing remains an open question.
Xycota is preparing a Canadian Clinical Trial Application (CTA) for XYCO-02 in adults with mild PTSD, working with contract research organization KGK Science. The company is not yet in formal dialogue with Health Canada. Key elements of the planned study include:
Preclinical studies in animals show that TrkB-dependent behavioral and synaptic effects can occur without 5-HT2A activation, and single-dose research in healthy adults has evaluated low-dose oral psilocybin to characterize perceptual thresholds. Whether repeated sub-perceptual dosing of XYCO-02 changes PTSD symptoms or maintains blinding in adults with mild PTSD remains to be tested in the planned clinical trial.
Peters J, Dieppa-Perea LM, Melendez LM, Quirk GJ. Induction of fear extinction with hippocampal-infralimbic BDNF. Science. 2010;328(5983):1288-1290. doi:10.1126/science.1186909.
Muthukumaraswamy SD, Forsyth A, Lumley T. Blinding and expectancy confounds in psychedelic randomized controlled trials. Expert Review of Clinical Pharmacology. 2021;14(9):1133-1152. doi:10.1080/17512433.2021.1933434.
Goodwin GM, Aaronson ST, Alvarez O, et al. Single-dose psilocybin for a treatment-resistant episode of major depression. New England Journal of Medicine. 2022;387(18):1637-1648. doi:10.1056/NEJMoa2206443.
Moliner R, Girych M, Brunello CA, et al. Psychedelics promote plasticity by directly binding to BDNF receptor TrkB. Nature Neuroscience. 2023;26(6):1032–1041. doi:10.1038/s41593-023-01316-5.
Ascone F, Buzzelli V, Mottarlini F, et al. Neuropsychopharmacology (2026), 51(8):1454-1463. doi:10.1038/s41386-026-02361-x.
Levy-Cooperman N, et al. Single-ascending-dose study of oral psilocybin in healthy adults. Pharmaceuticals. 2026. PMID: 42797541.