Exploring the Therapeutic Effects of Psychedelics Administered to Military Veterans in Naturalistic Retreat Settings

Military veterans face elevated rates of mental health problems, notably post-traumatic stress disorder (PTSD), frequently co-occurring with depression, substance use and difficulties reintegrating into civilian life. Calnan and colleagues note that existing first-line treatments for PTSD, including manualised psychotherapies and pharmacotherapies, show substantial non-response and dropout, and that many veterans do not access care because of barriers such as stigma and limited availability. The authors argue that conventional approaches often underemphasise community and social support, despite evidence that peer connection and shared experience are important for veterans' recovery. This observational study explores whether psychedelic retreat programmes, which combine administration of psychedelic medicines with group-based preparation, ceremonial dosing and integration, are associated with improvements in mental health and civilian reintegration among veterans. The investigators hypothesised that attendance at a retreat would yield significant, positive changes across multiple measures of psychological distress and reintegration, and that participants with worse baseline scores would show larger proportional improvements. The study therefore examines both symptom change across a battery of questionnaires and the relationship between initial severity and percentage improvement following the retreat experience.

Design and recruitment: The study used a naturalistic, observational pre–post design. Veterans who had already confirmed attendance at a Heroic Hearts Project retreat were invited to self-enrol via email. All participants provided informed consent and the study received institutional ethics approval (Imperial College Research Ethics Committee, reference 18IC4346). Retreat eligibility screening by the provider excluded people with a history of psychotic disorders or borderline personality disorder, those on antidepressants, antipsychotics, monoamine oxidase inhibitors or certain supplements, and those deemed psychologically unsuitable. Participants and setting: Data were collected from 58 veterans (44 male, 14 female; mean age ≈ 40.9 years). Most attendees (n = 45) took part in ayahuasca retreats held in Peru, while 13 attended psilocybin retreats held in Jamaica. Substance assignment was determined by retreat availability rather than random allocation. Retreat participants completed remote individual and group coaching sessions both before travel and during the integration phase after the retreat. Intervention and dosing: Retreats were residential and immersive, typically lasting 5–7 days. Ayahuasca ceremonies comprised three consecutive 6–10 hour sessions, with doses titrated by local facilitators; psilocybin was administered as a brewed tea with individualized dosing (Session 1: 1.5–3.5 g; Session 2: 3–5 g) and optional 1 g boosters. Guides provided preparation and integration support; participants remained at the retreat site for the programme duration. Measures and timing: Participants completed a battery of eight self-report instruments up to 4 weeks before travel (baseline) and again 4 weeks after returning and completing integration. Key instruments included the Patient Health Questionnaire (PHQ-9) for depression, the PTSD Checklist (PCL-5) for PTSD symptoms, the Military to Civilian Questionnaire (M2C-Q) for reintegration, the State-Trait Anxiety Inventory—Trait scale (STAI-T), the Rivermead Post-Concussion Symptoms Questionnaire (RPQ), the QOLIBRI (quality of life after brain injury), SWEMWBS (mental well-being) and PROMIS sleep measures. The authors normalised scores to percentage improvement to enable comparisons across instruments with different scales and directionality. Statistical analysis: Analyses were performed in SPSS 28. Paired two-tailed t-tests compared baseline and follow-up scores; Cohen's d was calculated for effect sizes (thresholds defined by the authors), and the Holm–Bonferroni procedure was applied to correct for multiple comparisons. Participants with missing values were excluded from affected analyses. Exploratory post-hoc linear regressions examined the relationship between baseline severity and percent improvement for the two measures with largest average change. Post-hoc power calculations using G*Power were reported.

Sample characteristics: Fifty-eight veterans provided baseline data; 47 (81%) reported a PTSD diagnosis. The majority attended ayahuasca retreats (n = 45), and 13 attended psilocybin retreats. Sixteen participants (≈32.5%) were psychedelic-naïve prior to the retreat. Primary pre–post outcomes: Paired-sample t-tests indicated statistically significant improvements from baseline to 4-week follow-up across all eight self-report measures, with effect sizes described by the authors as medium to very large. Significant reductions were reported for depression (PHQ-9; p < 0.001, SD = 6.70, 95% CI [6.09, 9.61]), PTSD symptoms (PCL-5; p < 0.001, SD = 18.68, 95% CI not fully legible in the extraction), post-concussion symptoms (RPQ; p < 0.001, SD = 14.36), trait anxiety (STAI-T; p < 0.001, SD = 10.19), and improvements in mental well-being (SWEMWBS; p < 0.001, SD = 4.96), quality of life after brain injury (QOLIBRI; p < 0.001, SD = 16.06) and sleep (PROMIS; p < 0.001, SD = 11.91). The M2C-Q (reintegration) also showed a significant improvement (p < 0.001, SD = 0.84). Subgroup comparisons by substance and gender: When outcomes were expressed as percentage improvements, participants attending psilocybin retreats exhibited larger average percent reductions than the ayahuasca group on most measures: PHQ-9 (38.0% vs 26.5%), STAI-T (30.4% vs 22.5%), RPQ (30.5% vs 20.8%) and M2C-Q (25.8% vs 15.7%). Conversely, PTSD symptoms improved slightly more in the ayahuasca group (26.4%) than the psilocybin group (24.8%). Gender-stratified percentage improvements showed males generally had greater gains in depression, anxiety, quality of life after brain injury and reintegration, while females showed a larger percent improvement in PTSD symptoms (female 32.1% vs male 24.1%). The authors note the small number of female participants limits generalisability. Relationship with baseline severity and power: Visual inspection and post-hoc regression indicated that higher baseline severity predicted larger percentage improvements. The extracted text reports regression results as PHQ-8 R2 = 0.544, p < 0.001 and PCL-5 R2 = 0.336, p < 0.001; however, the measures elsewhere are referred to as PHQ-9, so there is an inconsistency in the extracted report. Post-hoc power calculations indicated high statistical power for the paired t-tests (>0.99), attributed to large observed effect sizes.

Calnan and colleagues interpret their findings as evidence that attendance at a psychedelic retreat, when combined with preparatory and integration coaching and a communal setting, was associated with broad improvements in veterans' psychological health and self-reported civilian reintegration at 4 weeks. The authors highlight large reductions in depression, anxiety and PTSD symptoms, and note an especially large improvement in post-concussion-related symptoms measured by the RPQ, which they link to the high prevalence of head trauma in military cohorts. The use of the M2C-Q is presented as a novel contribution, indicating an 18% average improvement in reintegration-related difficulties. The discussion situates these results within emerging literature suggesting therapeutic benefits of psychedelics and emphasises that communal or ceremonial aspects of retreats may contribute to outcomes by fostering social support and shared processing. Substance-specific patterns are discussed: psilocybin retreats were associated with larger improvements across multiple domains, whereas ayahuasca retreats showed a modestly greater effect on PTSD symptoms, a pattern the authors link to prior observations of trauma re-experiencing during ayahuasca ceremonies that may facilitate meaning-making. Gender differences are reported and considered potentially attributable to sex-specific pharmacokinetics or other factors; the limited female sample size is acknowledged. Key limitations acknowledged by the study team include the absence of a control or placebo group, non-randomised self-selection into retreats, potential expectancy effects, the inability of primary t-test analyses to adjust for covariates (for example prior psychedelic experience or intervening life events), lack of systematic adverse-event recording and absence of individual dose data. The authors also note the small, non-diverse sample and short follow-up period (minimum 4 weeks) as limits on generalisability and the ability to infer durability of effects. They recommend future research employ controlled comparisons (for example matched non-psychedelic wellness retreats), record dosing and adverse events, use analytical methods that adjust for covariates, recruit gender-balanced and larger samples, and include longer and more frequent follow-ups. The authors also call for studies that disentangle the pharmacological action of psychedelics from the contextual and communal components of retreat programmes.

The study is presented as the first to assess psychedelic retreat attendance in military veterans with explicit measurement of civilian reintegration, reporting significant improvements across multiple domains of psychological and general well-being at 4 weeks. Calnan and colleagues conclude that psychedelics administered in a retreat context may provide a multi-dimensional therapeutic avenue for veterans, with preliminary evidence that psilocybin and ayahuasca could have different relative benefits depending on symptom profile. They emphasise the need for future work to separate pharmacological from contextual effects and to test these observations with more rigorous, controlled, and longer-term study designs.