Improved mental health outcomes and normalised spontaneous EEG activity in veterans reporting a history of traumatic brain injuries following participation in a psilocybin retreat

Psilocybin is a serotonergic psychedelic that acts mainly at 5-HT2A receptors and has been proposed to promote neuroplasticity and to reorganise functional connectivity in networks supporting emotion and cognition. Veterans are at elevated risk of traumatic brain injury (TBI) and commonly experience chronic neurological and psychiatric sequelae such as depression, anxiety and post-traumatic stress disorder (PTSD). Electroencephalography (EEG) studies of TBI have repeatedly documented persistent abnormalities in spectral power and coherence, most notably elevated slow-wave activity in delta and theta bands and attenuated alpha and beta rhythms, which are thought to reflect disrupted thalamocortical and cortical network function. Blest-Hopley and colleagues set out to evaluate whether participation in residential psilocybin retreats was associated with improvements in mental health and concomitant changes in resting-state EEG among veterans reporting prior TBI. The authors hypothesised that retreat attendance would reduce delta power and normalise theta activity, while increasing alpha and beta power and coherence, with effects localising primarily to frontal and temporal regions. Psychological outcomes were to be measured with validated questionnaires and neurofunctional changes assessed using pre- and post-retreat EEG recordings collected at the retreat site.

This was an observational, naturalistic study of veterans recruited via the Heroic Hearts Project who attended one of two six-day psilocybin retreats in Jamaica organised by Beckley Retreats. Inclusion required a self-reported history of suspected chronic TBI and current psychological distress; exclusion criteria applied by the programme and medical staff excluded participants with serious cardiovascular conditions, psychotic or personality disorders, or other contraindicated medical or psychiatric conditions. Participants completed three individual and three group preparatory coaching sessions prior to travel. At the time of retreat attendance none were taking contraindicated psychoactive medications; medication histories were reviewed and any necessary discontinuations were managed under physician supervision. The intervention comprised two ceremonial administrations of dried Psilocybe cubensis mushroom tea spaced 48 hours apart. Initial dried mushroom doses ranged from 1.5 g to 3.5 g with an option to increase the second dose typically to 3 g–5 g; the authors estimated these ranges corresponded approximately to 15–35 mg psilocybin for the first session but acknowledged uncertainty due to natural product variability. Small booster doses (up to 1 g) could be offered within the early onset window. All dosing decisions were made collaboratively between participants and retreat staff and sessions were facilitated by experienced personnel. Psychological measures were collected remotely at baseline (four weeks pre-retreat) and at follow-up (four weeks post-retreat) using validated questionnaires administered on a digital platform. Key instruments reported include the PTSD Checklist for DSM-5 (PCL-5), Patient Health Questionnaire (PHQ-9), State-Trait Anxiety Inventory (STAI), Rivermead Post-Concussion Questionnaire (RPQ), Quality of Life after Brain Injury (Qolibri-OS), PROMIS Sleep Disturbance scale and the Warwick-Edinburgh Mental Well-being Scale (W-EMWS), among others. Resting-state EEG was recorded at the retreat site using a 19-electrode dry-cap system (10/20 montage) with participants seated, eyes open. Recordings were obtained on day one prior to any psilocybin and again on the final day at least 36 hours after the last ceremony. EEG analyses focused on canonical frequency bands (delta, theta, alpha, beta), spectral power, spatial variance, coherence/connectivity matrices and multivariate approaches including canonical correlation analysis (CCA) and representational similarity analysis. Behavioural pre-post comparisons used paired t-tests (two-tailed), with Bonferroni correction for multiple testing; EEG within-subject comparisons used Wilcoxon signed-rank tests (a non-parametric paired test) with false discovery rate correction across electrodes. Subgroup analyses stratified participants by prior psychedelic use (psychedelic-experienced versus naive).

Twenty-one male veterans provided EEG data and a subset of 13 participants completed the psychological questionnaires at both timepoints. Mean age for the EEG group was 38.52 years (SD = 6.20) and 38.15 years (SD = 6.61) for the questionnaire completers. Most participants were from the United States and educational and employment distributions were reported descriptively. Behavioural outcomes (n = 13) showed statistically significant pre-to post-retreat improvements on multiple measures. Depressive symptoms on the PHQ-9 decreased from a baseline mean of 15.538 (SD = 4.115) to 5.308 (SD = 5.186), p < 0.001, and this survived Bonferroni correction. State anxiety (STAI) decreased from 53.769 (SD = 7.259) to 38.500 (SD = 11.533), p < 0.001, also surviving correction. The Rivermead Post-Concussion Questionnaire (RPQ) decreased from 34.692 (SD = 9.013) to 18.538 (SD = 12.258), p < 0.001 (survived correction). Quality of life (Qolibri-OS) increased from 41.614 (SD = 13.764) to 67.522 (SD = 17.277), p < 0.001, surviving correction. The Military to Civilian Questionnaire (M2C) scores, indicating reintegration difficulties, decreased from 2.174 (SD = 0.677) to 0.959 (SD = 0.871), p < 0.001, and this result also survived correction. PTSD symptoms measured by PCL-5 fell from 40.769 (SD = 16.799) to 20.923 (SD = 19.410), p = 0.010, but this change did not survive Bonferroni adjustment (adjusted p = 0.235). Measures of sleep disturbance and mental well-being showed improvements that reached uncorrected significance but did not consistently survive multiple-comparisons correction. Subgroup analyses stratified by prior psychedelic exposure indicated that participants with previous psychedelic use (n = 9) showed statistically significant reductions across the primary psychological measures (PHQ-9, STAI, RPQ, M2C, PROMIS-SD) and improvements in quality of life. Psychedelic-naïve participants (n = 4) exhibited directionally similar changes that did not reach statistical significance; the authors note these subgroup comparisons are limited by small sample sizes. EEG findings (n = 21) indicated systematic changes after the retreat. Spectral analyses revealed reductions in delta power and theta power localized especially to frontal and temporal regions, and modulation of alpha and beta activity with increased beta power observed in frontal and central regions. Spatial variance of band power increased post-retreat for theta (p = 4.17 × 10^-6), alpha (p = 1.00 × 10^-6) and beta (p = 1.00 × 10^-6) bands, while delta variance showed a more modest increase (p ≈ 0.039). Pairwise and electrode-wise comparisons identified enhanced inter-band distinction—particularly increased segregation between delta and higher-frequency bands—at electrodes including P3, C3, C4, P4, Cz, T5 and A2. Connectivity analyses showed changes in coherence patterns: pre-retreat recordings displayed widespread moderate connectivity without clear clustering, whereas post-retreat matrices exhibited strengthened connectivity especially in frontal and central regions. The authors report the delta band showed the most pronounced post-treatment enhancement in connectivity strength, while beta-band connectivity remained widespread with some frontal strengthening. Multivariate analyses (CCA, representational similarity) suggested a post-retreat reconfiguration toward more homogeneous within-subject patterns and increased inter-individual convergence. The authors note they did not collect adverse event data and therefore provide no safety statistics.

Blest-Hopley and colleagues interpret their observational findings as evidence that participation in a structured psilocybin retreat was associated with multidimensional improvements in mental health and measurable changes in resting-state EEG among veterans reporting prior TBI. After Bonferroni correction, statistically robust improvements were observed in depressive symptoms, state anxiety, post-concussive symptoms, quality of life and civilian reintegration. PTSD symptom reductions and other wellbeing measures improved but did not survive correction and are therefore presented cautiously. In terms of neurophysiology, the authors propose that reductions in delta and theta power and increased spatial variance and inter-band segregation reflect enhanced oscillatory specificity and improved neural integration, particularly across frontal, temporal and central regions implicated in TBI. Increased beta activity and frontal-parietal connectivity are discussed as consistent with prior work linking beta oscillations to recovery trajectories. Multivariate findings suggesting more homogeneous post-retreat brain representations are interpreted as potential indicators of network reorganisation and greater functional synchronisation. The authors acknowledge several limitations that constrain causal inference and generalisability. The study is observational, unblinded and lacks a control group, so non-specific factors such as expectancy, group support, natural recovery or other retreat elements may account for some or all observed changes. Sample sizes were small (EEG n = 21, psychological n = 13), subgroup analyses were underpowered (psychedelic-naïve n = 4), and adverse events were not collected. EEG acquisition used a dry-cap system with potential signal-quality limitations, and post-retreat EEGs were obtained at least 36 hours after dosing so residual drug effects cannot be fully excluded. The authors also note pharmacokinetic uncertainty arising from natural mushroom preparations and emphasise that mechanistic biological claims (for example regarding synaptogenesis, BDNF, mTOR, or anti-inflammatory effects) remain speculative because corresponding biomarkers were not measured in this protocol. Given these caveats, the authors recommend larger, rigorously controlled studies—ideally randomised, placebo-controlled trials with standardised dosing, comprehensive safety monitoring, longer follow-up and more granular connectivity metrics—to determine whether the observed clinical and EEG changes can be causally attributed to psilocybin and to clarify underlying mechanisms. They also suggest future work should be powered to test whether specific EEG changes predict or mediate clinical improvements.

The study reports that veterans with self-reported TBI who attended structured psilocybin retreats experienced significant reductions in depressive and anxiety symptoms, improvements in quality of life and reintegration, and changes in resting-state EEG indicative of reduced slow-wave dominance and increased higher-frequency differentiation and connectivity. While these findings support the potential therapeutic value of psilocybin retreats for this population, the authors emphasise that the observational design, small sample sizes, lack of control conditions and other methodological constraints preclude definitive attribution of effects to psilocybin alone. They call for larger, controlled trials with standardised dosing, biomarker assessment and comprehensive safety monitoring to validate and extend these preliminary observations.