Symmetrical Global Mental Health (Sym-GMH): Ayahuasca and shipibo traditional medicine for lasting changes in personality and quality of life

The authors frame the paper within Global Mental Health, arguing that mental health care should not only export biomedical models from the Global North but also examine how traditional medical systems may contribute through non-extractive, culturally respectful exchange. They present ayahuasca and Shipibo traditional medicine as an important example because interest in these practices has expanded in Western countries, yet their longer-term psychological effects in a traditional Amazonian setting remain insufficiently characterised. The study set out to examine whether participation in Shipibo-led ayahuasca retreats was associated with lasting changes in personality, quality of life, decentering, and psychiatric symptoms among Western visitors over 12 months. The authors also aimed to place these findings within their proposed Symmetrical Global Mental Health (Sym-GMH) framework, in which traditional and Western systems are evaluated as reciprocal rather than one-directional forms of knowledge exchange.

Bouso and colleagues conducted a prospective longitudinal study using data from people who attended the Temple of the Way of Light retreat centre in the Peruvian Amazon between 2015 and 2017, with 12-month follow-up completed in 2018. Participants were adults who voluntarily agreed to join the study after deciding to attend a retreat. The extracted text indicates that the centre excluded people with a history of certain psychiatric disorders, current use of medications such as MAOIs or SSRIs, heart disease, chronic high blood pressure, pregnancy, and current or past organic brain disease. The analysis for this paper used the subset of participants who completed all relevant assessments, which amounted to 264 people. The retreat setting involved Shipibo healers leading nighttime ceremonies in silence and darkness, alongside some Western supportive practices such as yoga, meditation, and psychological counselling. The number of ceremonies varied by retreat length. The authors also report that two ayahuasca batches prepared at the centre were chemically analysed by liquid chromatography-mass spectrometry and contained DMT, harmine, harmaline, and tetrahydroharmine, with no other psychoactive compounds detected. Outcome measures included the NEO Five-Factor Inventory (NEO-FFI) for personality, the WHOQOL-BREF for quality of life, the EQ-Decentering scale, and the SA-45 for psychiatric symptoms. Questionnaires were completed about 15 days before the retreat and again 12 months afterwards; ayahuasca experience questions were collected shortly after the retreat, with recent use followed up at 12 months. The authors also recorded lifetime and recent substance use, motivations for attending, satisfaction with the retreat, perceived long-term effects, and adverse effects. Analytically, the researchers transformed SA-45 scores into standard T scores and used a cutoff of 60 to indicate clinically relevant pathology. Personality scores were recoded into low, average, and high categories based on NEO-FFI norms. The statistical plan included descriptive analyses, paired-sample t-tests, Stuart-Maxwell tests of marginal homogeneity for changes in categorical distributions, McNemar tests when distributions changed significantly, chi-square tests for associations between personality traits and motivations, Pearson correlations, and multivariate linear regression models to test whether baseline personality predicted changes in quality of life while adjusting for age, sex, and baseline scores. Effect sizes were estimated with Cohen's d and 95% confidence intervals using bootstrap samples.

Of 950 recruited participants, 264 completed the baseline and 12-month assessments and were included in the analysis. The sample had a mean age of 40.96 years, 50.4% were female, most were from English-speaking Western countries, and 85.2% had a university degree or higher. The authors state that dropout analyses did not indicate obvious demographic bias among those lost to follow-up. At baseline, self-reported psychological problems were common, including depression in 27.3%, anxiety in 33.7%, grief in 12.5%, PTSD in 6.1%, and drug addiction in 3.8%. Despite this, only 45.3% of those reporting psychological problems said they had a formal psychological diagnosis. Recent substance use was also common: 76.9% reported any drug use in the past month, with alcohol the most frequent substance, followed by cannabis and tobacco. Most participants were ayahuasca-naïve. On the SA-45, most subscales remained below the clinical cutoff, although Phobic Anxiety and Psychoticism were slightly above 60. Over 12 months, participants showed significant improvements in three of the five personality traits: Neuroticism decreased, while Extraversion and Openness increased. The reported effect sizes were modest for Extraversion and Openness and moderate for Neuroticism. Agreeableness and Conscientiousness did not change significantly. When personality scores were recoded into categories, only Neuroticism showed a significant shift: the High category fell from 39.77% to 28.57%, and the Low category increased from 23.94% to 39.00%. Quality of life improved significantly in all four WHOQOL-BREF domains. Cohen's d values were 0.62 for physical health, 0.78 for psychological health, 0.71 for social relationships, and 0.50 for environment. Decentering also increased substantially, with a Cohen's d of 0.87. Baseline psychopathology correlated with later personality and decentering. Higher baseline Global Severity Index and Positive Symptom Total scores were associated with higher Neuroticism at follow-up and lower Extraversion, Agreeableness, and Conscientiousness. Baseline distress was also associated with lower decentering at follow-up. Decentering, in turn, was negatively associated with Neuroticism and positively associated with Extraversion, Agreeableness, Conscientiousness, and, to a smaller extent, Openness. In the regression models, baseline Extraversion was the only personality trait that consistently predicted greater improvement in all quality-of-life domains. Higher Conscientiousness was associated with a small decline in physical health, and there was a marginal, non-significant trend for psychological well-being. Baseline psychopathology did not predict changes in quality of life. At the 12-month follow-up, 33.0% reported ayahuasca use in the previous year. The main reasons for use were spiritual growth, personal development, and therapeutic purposes, with no participants naming recreational use or escapism as their primary motivation. Among all participants, the retreat was viewed most often as being shaped by the ayahuasca experiences themselves and by the work of the Shipibo healers. Most respondents reported high satisfaction with the retreat and with ayahuasca itself. Among those who answered the follow-up question, 84% said therapeutic effects persisted throughout the year. Long-term benefits were reported by 91.7%, most commonly in spiritual well-being, personal well-being, mental health, social relationships, lifestyle, and physical health. Only 2.3% reported harm, injury, or long-term adverse effects, most often affecting mental health and social relationships; no long-term physical adverse effects were reported. The authors also note changes in substance use across time, including an increase in past-month substance use overall, but they specify that this increase was driven by tobacco, whereas other substances decreased. They report that MDMA and other drugs did not show significant categorical changes.

The authors interpret the findings as support for their Sym-GMH framework, arguing that traditional Shipibo healing practices can contribute meaningfully to global mental health when evaluated in their cultural context rather than reduced to an isolated drug effect. They emphasise that the retreat setting should be understood as a therapeutic system combining the brew, the healers, ritual structure, and other contextual elements, not simply as ayahuasca administration. They place the findings alongside earlier research showing that ayahuasca and other psychedelics can be associated with improvements in mood, decentering, quality of life, and, in some studies, personality change. They note that the personality results remain mixed across the wider literature, but argue that their study adds evidence of longer-term change, especially in Neuroticism, and that the categorical shifts were particularly striking. The discussion highlights that a substantial part of the perceived healing was attributed by participants to the Shipibo healers and the ritual context rather than to ayahuasca alone. The authors interpret this as evidence that relational and ceremonial factors are central to outcomes, and they link this to the broader policy question of how psychedelics are being medicalised in strictly biomedical settings while traditional communal ceremonies are restricted in some countries. They also discuss the association between baseline distress, lower decentering, and poorer later personality profiles, suggesting that decentering may be relevant to resilience and harm reduction. On this basis, they propose that enhancing decentering could be useful in therapeutic or controlled psychedelic settings, especially for people with higher emotional vulnerability. The authors acknowledge several limitations. The main limitation was the lack of a control condition, which is typical for naturalistic work but restricts causal inference. They also note that the cultural homogeneity of the sample limits generalisability. More broadly, they say that applying a randomised clinical trial model to Shipibo traditional medicine may not fully fit the structure of the practice. They call for future research that includes more diverse populations and uses methods that preserve the integrity of traditional healing systems while still allowing rigorous evaluation. The discussion further addresses ethical and intercultural complexities, including the possibility of cultural appropriation, economic imbalance, neocolonial dynamics, and tensions over how ayahuasca is adapted for Western visitors. The authors argue that these issues do not undermine Sym-GMH but instead show why genuine intercultural dialogue and Indigenous perspectives are necessary for future work.

The authors conclude that the study supports the Sym-GMH concept by showing lasting improvements in Neuroticism, quality of life, and decentering after Shipibo-led ayahuasca retreats in Western participants. They argue that traditional medical systems can contribute to mental health through equitable, evidence-based exchange rather than colonial extraction. They say that future research should combine naturalistic and clinical approaches, while respecting cultural integrity, and that health policy should recognise different healing modalities and the ethical risks of colonialism, extractivism, and cultural appropriation.