Psychological and neuropsychological assessment of regular hoasca users

Hoasca (also called ayahuasca) is a decoction combining Psychotria viridis, which contains N,N-dimethyltryptamine (DMT), and Banisteriopsis caapi, which contains β-carbolines that act as monoamine oxidase inhibitors and render DMT orally active. Acute ingestion produces dose-dependent perceptual, cognitive and affective effects that peak within about 60–120 minutes and largely resolve within 4–6 hours. Interest in the brew has spread beyond Amazonian magico-religious contexts to syncretic Brazilian churches such as União do Vegetal (UDV) and to non-religious users worldwide, prompting regulatory and scientific attention to possible long-term psychological and neuropsychological effects of repeated ritual use. Cesar and colleagues designed a cross-sectional, case-controlled study to evaluate whether regular, ritualised hoasca use within a UDV congregation in the United States is associated with differences in substance use, mood, personality, quality of life, religiosity, and neuropsychological functioning. The study aimed to address a gap in prior research by matching hoasca users to controls on socio-economic status and church attendance, thereby attempting to separate effects of the substance from effects associated with organised religion and communal support.

This was a cross-sectional, case-control comparison of 30 UDV members who regularly drank hoasca during religious services and 27 non-hoasca-using control subjects from other organised religious groups in the same geographic area. Inclusion criteria required participants to be aged 18 or older, fluent in English and able to provide informed consent; current use of psychiatric or neurological medication was an exclusion. Controls were matched to UDV participants by gender and age (±2 years). The study received institutional human subjects approval. Participants were recruited via the local UDV congregation for the hoasca group and by public presentations, flyers and assistance from local clergy for controls. Evaluations took place at the University of New Mexico Center for Psychiatric Research or in a quiet private area near the UDV church. Participants were instructed to abstain from alcohol for two days before testing, from stimulants including caffeine and tobacco for one hour before testing, and UDV members were asked to refrain from drinking hoasca for at least six days prior to assessment. Measures covered socio-economic variables (CASAA SES questionnaire), religiosity and ritual attendance (a bespoke questionnaire, the Duke University Religion Index — DUREL — and the Daily Spiritual Experience Scale — DSES), quality of life (SF-36), mood (30-item shortened Profile of Mood States — POMS), personality (Big Five Inventory — BFI), impulsivity (Barratt Impulsiveness Scale — BIS-11) and substance use history (Drug/Alcohol section of the Addiction Severity Index, 5th edition). Neuropsychological testing included the American Nelson Adult Reading Test (AMNART) to estimate premorbid intelligence, the California Verbal Learning Test (CVLT) including an interference list measure, and additional tests listed in the paper: Stroop, Trail Making Test, Rey–Osterrieth Complex Figure, and Conners Continuous Performance Test, plus measures of fine motor and visuospatial-constructional ability. Statistical analyses used chi-squared and Fisher's exact tests for categorical variables and Mann–Whitney U tests for continuous variables because many failed normality (Shapiro–Wilk p ≤ 0.05). Effect sizes were reported as Cramer's V for categorical tests and r = Z/√N for Mann–Whitney tests. Within the UDV sample, Spearman correlations examined associations between hoasca attendance (total lifetime months of regular attendance and number of ceremonies in the prior 12 months) and continuous outcomes; binomial (logistic) regression assessed relationships with dichotomous outcomes, with Box–Tidwell checks for linearity and studentized residuals to detect outliers. Statistical significance was set at p ≤ 0.05.

Demographically, the two groups did not differ significantly in age, gender or socio-economic indicators. Within the UDV sample, the number of hoasca sessions attended in the previous 12 months correlated positively with DUREL-assessed Organizational Religious Activity (rs = .39, p = 0.034). On substance-use measures (ASI), the UDV group reported greater lifetime past use of alcohol to intoxication (χ2(1) = 7.402, p = 0.007, φc = .36) and greater lifetime cannabis use (χ2(1) = 11.315, p = 0.001, φc = .45) than controls. By contrast, recent alcohol use (any use in the previous 30 days) was significantly lower in the UDV group (χ2(1) = 18.192, p < 0.001, φc = .57). Logistic regression showed that increasing total lifetime months of regular attendance at hoasca rituals was associated with a decreased likelihood of lifetime past use of alcohol to intoxication (B = -0.022; p = 0.034; OR = 0.979). The number of recent alcohol users in the UDV sample was too small (two of 30) to permit regression analyses for recent use. On self-report mood and personality measures, the UDV group scored lower on POMS-assessed Depression (p = 0.043, r = .27) and Confusion (p = 0.032, r = .29), and higher on BFI Agreeableness (p = 0.028, r = .29) and Openness (p = 0.037, r = .28) relative to controls. Quality-of-life scores on the SF-36 domain Role limitations due to physical health were higher in the UDV group (p = 0.035, r = .28), and total lifetime months of hoasca attendance correlated positively with that SF-36 domain (rs = .39, p = 0.032). Neuropsychological testing showed no group differences across most measures of cognitive function, including premorbid intelligence estimates (AMNART), attention, executive function, visuospatial ability, and fine motor control. The single exception was the CVLT interference list: UDV members performed better, indicating less susceptibility to proactive interference during verbal learning (U = 279, p = 0.040, r = .27). CVLT List B performance did not correlate with hoasca attendance variables. Overall, the investigators report no evidence of deleterious neuropsychological effects associated with regular ritual hoasca use in this sample.

Cesar and colleagues interpret these findings as broadly reassuring regarding long-term neuropsychological safety of ritual hoasca use within the UDV context. Compared with socio-economically and church-attendance matched controls, UDV members showed no cognitive deficits on a battery of standard neuropsychological tests and, in one verbal learning measure, performed better than controls. The authors emphasise that, aside from the single CVLT finding, effect sizes were generally small and there were no correlations linking level of hoasca use to poorer cognitive performance. With respect to psychological and behavioural outcomes, the UDV group reported less current depression and confusion, higher Agreeableness and Openness, and improved role functioning related to physical health. The study team highlights reduced recent alcohol consumption among UDV members despite greater lifetime exposure to alcohol and cannabis, and reports that greater lifetime hoasca attendance was associated with lower odds of past heavy alcohol use. The authors note that organisational and social features of the UDV — doctrinal teachings, community practices and norms — may contribute to these positive outcomes, and that ritual experience itself might play a role: they cite prior work linking intense psychedelic-induced mystical-type experiences to increases in Openness and to improved drinking outcomes in psilocybin studies, and they discuss possible pharmacological mechanisms such as harmine-related increases in brain-derived neurotrophic factor and animal data suggesting hoasca-related effects on ethanol sensitisation. Key limitations are acknowledged. The cross-sectional design cannot establish causality and is vulnerable to selection bias or survivorship effects, since individuals who do not adapt to UDV practice may leave and thus not be captured. Multiple comparisons increase the chance of Type I error. The authors therefore call for prospective longitudinal assessments of new hoasca users and neuroimaging studies to better characterise causal effects and underlying neural mechanisms. They also note that organisational differences between religious groups and local norms (for example UDV attitudes towards cannabis) may explain discrepancies with other studies of hoasca-using populations. In sum, the investigators position this study as the most comprehensive North American evaluation of ritual hoasca users to date and conclude that, within the sample studied, regular religious use of hoasca was not associated with neuropsychological impairment and was associated with some favourable psychological and substance-use-related measures, while emphasising the need for prospective and mechanistic research to confirm and extend these findings.

The authors conclude that, compared with a carefully matched control group, UDV members who regularly use hoasca demonstrated better mood, personality and quality-of-life scores, no widespread cognitive deficits and evidence of reduced recent alcohol use. They caution that the cross-sectional design and potential selection bias limit causal inference and recommend prospective mental health and neuropsychological studies, along with neuroimaging work, to further assess long-term effects and mechanisms of hoasca use.