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About this resource
This is an English version of a 2012 longitudinal observational study comparing adults who used ayahuasca regularly over the long term in religious and ceremonial settings with religiously active adults who did not use ayahuasca. Personality, psychiatric symptoms, life attitudes, and neuropsychological tests including attention, memory, and executive function were assessed at baseline, and some participants were reassessed approximately 1 year later.
The study is important evidence on whether clear impairment was detected among long-term users, but participants were not randomly assigned to user and nonuser groups. Even if groups differ, the design cannot conclude that ayahuasca caused improvement or deterioration. Because it examines people who remained in their communities and were able to participate over the long term, survivor and selection biases may also make people who left after experiencing problems less visible.
Study design
The study included 127 regular ceremonial users and 115 active religious participants who did not use ayahuasca. The user group had a history of use for at least a defined period and was recruited from several communities. Choosing controls involved in religion rather than simply a nonreligious general-population group was an effort to reduce confounding from some aspects of community participation and religiosity.
Assessments included scales of psychiatric symptoms, personality traits, psychosocial adaptation, meaning and attitudes toward life, and several neuropsychological tasks. Fewer participants remained at the 1-year follow-up than at baseline. Analyses addressed between-group comparisons and change over time, but could not fully control amount of use, ceremonial content, lifestyle, education, culture, pre-existing personality differences, and other factors.
Content
The authors set concerns that long-term ayahuasca use might be associated with psychopathology or cognitive impairment alongside users’ reports of positive psychosocial change. The study used not only self-report but also tests of attention, working memory, response inhibition, and other functions to examine whether a consistent impairment signal emerged across multiple domains.
The groups differed in personality and life attitudes. The user group was reported to have lower scores on some psychiatric-symptom measures and equal or better performance on some neuropsychological tasks. It remains possible, however, that people with those characteristics were more likely to join and remain in the communities, or that community support and lifestyle contributed.
Reassessment after 1 year adds information beyond a single cross-sectional comparison, because pronounced ongoing deterioration among long-term users might appear as change over time. Yet without randomization or measurements before use began, the data do not support a causal inference that use was protective.
Results
The authors concluded that, within the range of scales and tests used, they found no evidence of psychopathology or impaired neuropsychological function among long-term ceremonial users. On some measures, the user group had more favorable average values, and the pattern was broadly maintained after 1 year. This is an observation that no clear, general functional decline was detected among continuing participants in the communities studied.
The findings do not support conclusions that ayahuasca improves personality, prevents mental illness, or enhances cognition. Differences from the control group could be explained by pre-existing differences, cultural background, education, diet, community, selection, and attrition. An absence of group-average impairment also does not exclude adverse trajectories in a minority of individuals.
Limitations
The observational design, absence of random assignment, and lack of baseline measurements before use began limit causal interpretation. Long-term community participants may not represent people who left because of acute difficulties or health problems. Loss to follow-up can also make outcomes appear more favorable when only those who remain are assessed.
Caution is also needed regarding the meaning of psychological scales across cultures and languages, social desirability in self-report, and chance differences arising from multiple comparisons. Neuropsychological tasks measure particular functions but do not cover every area of daily life or rare psychiatric events. Brew composition and each person’s cumulative exposure were not standardized.
Using religious-community participants as controls helps align social background but is not suited to evaluating differences from the general population. If the groups’ cultural backgrounds were not fully identical, differences in familiarity with testing, response styles, and values may appear on the measures. Other life changes during the year could not be captured completely.
Safety
The absence of average impairment among selected long-term participants does not prove safety for every person, setting, or preparation. Acute cardiovascular changes, vomiting, interactions, psychosis-like or manic states, accidents, and effects during pregnancy cannot be evaluated by this comparison alone.
Community screening, ritual norms, and social support may also have contributed to the results. If so, the same observations cannot be transferred to an unsupervised setting that isolates the substance. This resource does not recommend beginning or continuing use.
The study concerns a population already able to sustain regular participation. Separate safety evidence is needed for first acute reactions, people who discontinued, use outside communities, and analog products with different constituents. “No evidence of impairment” is not the same expression as “no risk exists.”
The absence of average cognitive decline in long-term observation is an important negative finding, but it does not rule out functions beyond the selected tests or outcomes affecting very few people. Favorable group differences should likewise remain observations about the community and broader way of life, without attributing their cause to ayahuasca alone.
Observation and interpretation need to be read separately.
That distinction does not weaken the value of a long-term study; it preserves the precise boundaries of what was learned.
Source and rights
Original source: Bouso JC, et al. Personality, psychopathology, life attitudes and neuropsychological performance among ritual users of Ayahuasca: a longitudinal study. PLOS ONE. 2012;7(8):e42421. DOI: 10.1371/journal.pone.0042421.
The original article is published under a Creative Commons Attribution license. This page is a source-aligned English translation under that license, reorganized to make the study population, comparison, and boundaries of causal interpretation clear. Tables and figures are not reproduced.