Effects of an international ceremonial ayahuasca retreat on the diversity and community composition of the human gut microbiome: A preliminary observational single-arm pre-post study

Ayahuasca ceremonial retreats appear to alter our gut microbiome and gut diversity

This study provides early evidence that participation in an ayahuasca ceremonial retreat is associated with changes in gut microbiome diversity and community composition. The findings add to growing interest in the relationship between psychedelic experiences, lifestyle changes, and the gut–brain axis, but controlled studies are needed to determine whether ayahuasca itself—or related factors such as diet, stress reduction, social connection, and ritual practices—drive these microbial changes.

Key points

• Ayahuasca retreat participation was associated with changes in gut microbiome composition. Participants showed measurable shifts in the overall structure of their gut microbial communities after the retreat.

• The overall organization of the gut microbiome changed after the retreat experience. Analyses of microbial community composition (beta diversity) indicated that participants’ microbiome profiles differed before and after the retreat.

• Microbiome diversity itself did not significantly increase. The study did not find evidence that the retreat led to a general increase in microbial richness or alpha diversity; instead, changes were observed in the composition and relative abundance of microbial groups.

• Specific bacterial taxa changed in abundance following the retreat. Several bacterial groups showed increases or decreases after the retreat, suggesting that the experience was associated with alterations in the balance of gut microbial populations.

• The observed microbiome changes occurred within a complex ceremonial retreat environment. Participants experienced multiple potential influences, including ayahuasca ceremonies, dietary changes, travel, altered routines, meditation or spiritual practices, and social interactions. Therefore, the effects cannot be attributed to ayahuasca alone.

• The findings provide preliminary evidence for a relationship between psychedelic retreat experiences and the gut microbiome. The results add to emerging research on interactions between psychedelic experiences, lifestyle factors, and the gut–brain axis.

• The study does not establish causation. Because it used a single-arm pre–post design without a control group, it cannot determine whether ayahuasca directly caused the microbiome changes or whether they resulted from other aspects of the retreat.

• The results highlight the need for controlled studies. Future research with control groups, standardized ayahuasca exposure, dietary monitoring, and longer follow-up will be needed to identify the specific factors responsible for microbiome changes.

Abstract

Posttraumatic stress disorder (PTSD) is a mental health condition that can develop following exposure to a traumatic event, often with persistent anxiety and depressive symptoms. Recent research suggests the microbiome-gut-brain axis may play an important role in the etiology and pathophysiology of PTSD. At the same time, retreats incorporating psychedelic-assisted therapies have gained increasing attention as potential treatments for PTSD.

However, little is known about how participation in these retreats may affect the gut microbiome. Therefore, we conducted a preliminary observational single-arm pre-post study investigating the diversity and community composition of the gut microbiome pre/post participation in a retreat involving ceremonial ayahuasca use, as well as associations between microbiome features, PTSD symptoms, and personality traits. Participants included U.S. Veterans and non-Veterans with varied PTSD symptoms (N = 22). The international retreat took place over one week and included three ayahuasca ceremonies. PTSD Checklist for the DSM-5 (PCL-5) scores, Five-Factor Model (FFM) personality measures, and fecal samples were collected from participants pre/post retreat. Fecal samples were analyzed using 16S rRNA gene amplicon sequencing to assess gut microbiome diversity and community composition. PCL-5 scores decreased following the retreat, relative to baseline. Openness, Conscientiousness, Extraversion, and Agreeableness increased, while Neuroticism decreased. Measures of gut microbiome alpha diversity did not change. However, beta diversity analyses revealed a within-subjects shift in microbial community composition at the end of the retreat relative to baseline.

Post retreat there was an increase in the relative abundances of several short-chain fatty acid-producing bacteria associated with gut health, including Lachnospiraceae UCG-004, Colidextribacter, Oscillospira, and Blautia. Although the study design has limitations and does not establish causality, it highlights within-subjects effects of participation in an ayahuasca retreat on the gut microbiome, effects that should be evaluated further in future large randomized double-blind, placebo-controlled clinical trials.

Kessler, L. R., Dawud, L. M., Sterrett, J. D., Andersen, N. D., Elsayed, A. I., Gould, J. J., Pate, K. M., Campbell, W. K., Grigsby, J., Weiss, B. M., & Lowry, C. A. (2025). Effects of an international ceremonial ayahuasca retreat on the diversity and community composition of the human gut microbiome: A preliminary observational single-arm pre-post study. Brain Behavior and Immunity Integrative Volume 15, July 2026, 100182 Read Paper

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