As far as I know, this is the first longitudinal study on the use of ayahuasca, the Amazonian entheogenic mixture that (after the purging, which is an important element of the experience), offers one of the more intense and spiritual hallucinogenic experiences recorded. It is also one of the most healing experiences, especially for addictions according to Gabor Maté.
This study shows, convincingly, that ayahuasca users are well-adjusted, lacking in psychopathology, and more spiritual (higher self-transcendence scores) than the control group.
Before presenting the new study, here is a little background on ayahuasca.
Ayahuasca (aya-spirit/dead, waska-vine/rope) or Yage (ya-hey) are native Amazonian names for the jungle vine Banisteriopsis Caapi, and the medicinal tea prepared from it. Ayahuasca is used throughout the Upper Amazon to enable access to the visionary or mythological world that provides revelation, blessing, healing, and ontological solace (Dobkin de Rios 1972, Grof 1994, Andritsky 1984).
The Banisteriopsis caapi vine is a Malpighiaceous jungle liana found in the tropical regions of Peru, Bolivia, Panama, Brazil, the Orinoco of Venezuela and the Pacific Coast of Colombia/Ecuador. The vine is the common base ingredient of the Ayahuasca tea. B. caapi contains beta-carbolines that exhibit sedative, hypnotic, anti-depressant, monoamine oxidase inhibiting, and threshold visionary activity.
Ayahuasca is a synergystic potion. A wide variety of admixture plants is used by the indigenous tribes of the Upper Amazon. Vine-only brew is sometimes used. Most typically the vine is mixed with a tryptamine carrying plant. The foliage of Psychotria viridis (Chacruna) is the principal admixture of Ayahuasca potions employed throughout Peru and Brazil. In Columbia and Amazonian Ecuador, the plant Diplopterys cabrerana (Chaliponga) is often used instead.
These plants provide the “light” or the visionary qualities, but these tryptamine-containing plants are not orally active alone. The monoamine oxidase inhibiting action of the B. caapi vine makes it possible for the tryptamines to produce powerful visions. In turn, the admixture plants potentiate the Vine.
The combination of the Caapi vine with Chacruna or Chaliponga is sometimes known as a marriage of Power and Light. This marriage unlocks the full shamanic mareacion and its visionary mythological vistas.
This medicine has been used for millennia in order to enter the sacred supernatural world, to heal, divine, and worship.
The use of Ayahuasca may well be primordial, its use extending back to the earliest aboriginal inhabitants of the Upper Amazon region. Abstract liminal patterns such as zigzags, serrated lines and geometric forms found on ancient relics and traditional textiles, pottery and body art of various tribes represent the perceptual threshold between everyday and transpersonal realms of consciousness. These relics, combined with an abundance of myths describing the origin of Ayahuasca as deeply intertwined cosmologically with the creation of the universe, earth, and tribal people, indicate a long history of human use.
Ayahuasca is a revered and respected sacred medicine, considered a spiritual and physiological panacea par excellence, because its medicine can instruct in healing, visionary insight, and the art of using plants for various purposes. Sometimes it is referred to simply as La Medicina – the Medicine.
For indigenous people such as the Napo Runa of Ecuador, Ayahuasca is “the mother of all medicines” and “the mother of all plants.” Other peoples regard Ayahuasca as a Grandfather or Grandmother. Ayahuasca, “the Vine with a soul,” is perceived as a communicating being who guides, teaches, and heals. Ayahuasca also acts as a mediator and translator between the human and plant worlds, and teaches humans how to communicate with plants and use them for various purposes.
There's more to read if interested . . .
With that background, here is the new research article . . . that offers very interesting and positive evaluations of ritual users of ayahuasca.
Personality, Psychopathology, Life Attitudes and Neuropsychological Performance among Ritual Users of Ayahuasca: A Longitudinal Study1 Human Experimental Neuropsychopharmacology. IIB Sant Pau, Barcelona, Spain, 2 Centre d’Investigació de Medicaments. Servei de Farmacologia Clínica, Departament de Farmacologia i Terapèutica, Universitat Autònoma de Barcelona. Hospital de la Santa Creu i Sant Pau, Barcelona, Spain, 3 International Center for Ethnobotanical Education, Research and Service, ICEERS, Halsteren, Netherlands, 4 Unidad Farmacología Humana y Neurociencias, Instituto de Investigación Hospital del Mar-IMIM, Parc de Salut Mar, Universidad Autónoma de Barcelona, Barcelona, Spain, 5 Center UCM-ISCIII for Human Evolution and Behavior, Madrid, Spain, 6 Instituto de Etnopsicología Amazónica Aplicada (IDEAA), Barcelona, Spain, 7 Independent Researcher, Barcelona, Spain, 8 Departamento de Filosofia e Ciências Humanas, Universidade Estadual de Santa Cruz (UESC), Ilhéus, Bahia, Brazil, 9 Departamento de Psicología Biológica y de la Salud, Facultad de Psicología, Universidad Autónoma de Madrid (UAM). Cantoblanco, Madrid, Spain, 10 Prefeitura Municipal de Rio Branco, Conselho Estadual de Educação do Estado do Acre, Rio Branco, Acre, Brazil, 11 Centro de Investigación Biomédica en Red de Salud Mental, CIBERSAM, Barcelona, Spain
Citation: Bouso JC, González D, Fondevila S, Cutchet M, Fernández X, et al. (2012). Personality, Psychopathology, Life Attitudes and Neuropsychological Performance among Ritual Users of Ayahuasca: A Longitudinal Study. PLoS ONE 7(8): e42421. doi:10.1371/journal.pone.0042421
Do be sure to read the whole article, but I want to skip directly to the Discussion. The researchers looked at personality, psychopathology, neuropsychological functions, and life attitude and psychosocial well-being. In all realms, ayahuasca users scored higher than controls.
For lovers of details, this one is particularly relevant - the control group was chosen due to their spiritual practices, so that the groups would be evenly matched in terms of spirituality. Despite this, the ayahuasca group score higher on the Spiritual Orientation Inventory.
DiscussionIn this paper we present data from a field research study in which personality, mental health, life attitudes and neuropsychological performance were assessed in a large number of ritual ayahuasca users and their matched controls.
1. PersonalityThe TCI  was used to assess personality. Differences between ayahuasca users and controls were found in several of the temperament dimensions, which are believed to be genetically determined. Higher scores on Reward Dependence (RD) may reflect a feature allowing the group to adapt to a demanding environment such as the tropical rainforest. This interpretation is supported by the significant scores on the RD subdimensions Attachment (RD3) and Dependence (RD4), but not Sentimentality (RD1). This profile is probably useful for life in a small community and in a hostile ecological environment. Participants in the Jungle sample showed a trend to higher scores on Persistence than their urban counterparts. Higher scores on this temperament dimension could explain the adaptation capacity shown by these people to their environment, and the ability to persist as a group despite isolation. Additionally, Harm Avoidance (HA) was lower in the ayahuasca-using subjects, probably reflecting the strength in personality required to undergo regular ayahuasca sessions for long periods of time. It is interesting to note that there were no differences between groups in Novelty Seeking (NS) scores nor in its subscales, including Impulsiveness (NS2). Since high scores in NS and Impulsiveness have been associated with drug use , , the mere search for new experiences may not be the underlying reason of their involvement with ayahuasca. On the contrary, members of the ayahuasca religions report that the experiences transcend the merely perceptual or recreational aspects of psychoactive drug effects.
The analysis of Character dimensions showed that ayahuasca users scored significantly higher in Self-Transcendence (ST). Since all participants (users and controls) actively practiced some religion, and Character traits can be influenced by personal experience and culture, this finding could be interpreted as a direct effect of ayahuasca use. Self-Directedness (SD), another Character dimension, is consistently lower in the ayahuasca groups, and may also be related to ayahuasca intake. Used in a religious context, the potent psychotropic effects of ayahuasca may strengthen adherence to the doctrine. The lower Self-Directedness (SD) scores found may reflect the greater relevance of the community over the individual. At the same time, there were no differences between users and controls in Cooperativeness (C). So despite greater Self-Transcendence and spirituality in the ayahuasca-using group, willingness to cooperate with others was not different from that seen in more conventional religions. It would be very interesting to assess if subjects who have decided to leave the group and discontinue ayahuasca use share personality traits with the long-term users.
In a group of 15 long term urban ayahuasca users, Grob et al.  found lower scores on NS and HA and no differences in RD compared to 15 matched non-users, in line with our own results. The higher RD scores in our study, driven mainly by the Jungle sample, may reflect the difference in environment mentioned above. Another research group has found changes in the Temperament dimensions of the TCI after 6 months of regular ayahuasca use in a religious setting in subjects who were initially naïve to ayahuasca. However, these same subjects did not show changes in the Character dimensions . Based on these findings, a less conservative explanation for the differences observed in Temperament traits in the present study would be that they are a consequence and not the cause of ritual ayahuasca use. This would mean that ayahuasca may induce changes in personality traits traditionally considered inherited. A recent study in which high doses of psilocybin were administered in a supportive setting showed positive long term changes in Openness to Experiences . This temperament trait is considered to be the most substantially heritable trait in the Big Five personality model, and relatively stable through adulthood .
2. PsychopathologyThe analysis of psychopathology indicators showed the important finding that ayahuasca users scored significantly lower on all nine dimensions of the SCL-90-R. The two immediate explanations for this finding are that either ayahuasca has a low potential to induce psychopathology, or that samples of long-term users suffer from a self-selection bias by which only those who do not experience adverse psychological effects continue ayahuasca use. Regarding the second explanation it is worth mentioning that at follow-up lower scores were still seen on most dimensions, despite the loss in sample size. Similar findings have been reported in the literature. In a study where a group of 32 long term US ayahuasca users were assessed with the same instrument, scores were significantly lower than normative data for 7 of the 9 dimensions . Halpern et al.  did not find evidence either of psychopathology in a group of peyote (a mescaline-containing cactus) users when compared to controls. Grob et al.  did not find evidence of psychopathology in their ayahuasca-taking sample using the CIDI (Composite International Diagnostic Interview), despite the fact that in the retrospective assessment most subjects met criteria for psychiatric disorders prior to their religious use of ayahuasca. Another study with teenage members of an ayahuasca church did not find differences with the control group, but rather showed a tendency to an improvement in some measures of psychopathology . Barbosa et al. ,  also failed to find psychophatological symptoms both in the short-term after a first ritual ayahuasca experience, and at follow up 6 months after continued use. Some participants even showed a decrease in minor psychopathological symptoms.
In summary, though there are case reports describing psychiatric complications following ayahuasca intake , , it appears that current long-term users do not show higher psychopathology. One study reported that some experienced users even show reduced scores of panic and hopelessness while under the effects of the tea . Future research should assess not only long-term users but also ex-users to evaluate whether adverse psychological effects play any role in the decision to discontinue use. The apparent contradiction between reports of psychiatric crisis after acute ayahuasca and the absence of psychopathology in many chronic users should be studied in more detail.
One last consideration is the potential bias introduced by the self-assessment nature of the SCL-90-R. Subjects may have been inclined to give socially acceptable responses. However, scores on the PST subscale were always higher than 3–4. According to the interpretation norms for the SCL-90-R , low scores on this subscale would be indicative of a social desirability bias. Further support for the validity of our present findings is derived from results in the neuropsychological assessment (see below). Psychiatric disorders are commonly accompanied by neuropsychological deficits , , but these were not observed in the ayahuasca-using subjects in the present study.
3. Neuropsychological FunctionsBased on the administered tests and the Frontal Systems Behaviour Scales, we found no evidence of neuropsychological impairment in the ayahuasca-using group. Furthermore, in general terms they scored better than their respective comparison groups and these differences were maintained one year later.
These results do not fit the hypothesis of potential frontal impairment secondary to 5-HT2A receptor activation, and are more in line with prior observations in users of psychedelics. Grob et al.  found no working memory deficits in their sample of ayahuasca users, but rather an improvement in one memory subset. Da Silveira et al.  did not find deficits in the stroop and other neuropsychological tests in their group of adolescent ritual ayahuasca users. These users did not score differently than their control group in most variables. They did fare worse on some memory subtests, but results were within the normalcy range. Halpern et al.  did not find neuropsychological impairment in a group of long term peyote users from the Native American Church. Tests included the Stroop test, the Wisconsin Card Sorting Test and working memory tests. Although more research is needed before definite conclusions can be drawn regarding this drug class, based on the available evidence chronic use of psychedelics does not seem to cause cognitive impairment.
The lack of cognitive impairment in our ayahuasca users can not be attributed to a lack of sensitivity of the neuropsychological tests administered, as they were sensitive enough to differentiate between users and non users. The Stroop task and the Wisconsin Card Sorting Test tap various cognitive functions such as selective attention, behavioral inhibition, working memory and goal-directed behavior, and are sensitive to PFC damage . Also, these same tests have been found to detect neuropsychological impairment in various groups of drug abusers. For example, the Wisconsin Card Sorting Test has proven sensitive to detect flexibility impairments in non-addicted cocaine polydrug users (between 1–4 gr. of cocaine per month). This population showed more Perseverative Errors, fewer Categories Completed and worse Conceptual Level Responses than matched controls . Also, the Stroop test was sensitive to detect executive dysfunctions in individuals using alcohol , cocaine  and amphetamines . The same applies to the Letter-Number Sequencing task . However, the detection of differences between users and non-users is known to be influenced by the length of the abstinence period, the severity and duration of the addiction, the use of multiple drugs and the presence of associated psychopathology . In any case, better performance in the drug-using group is rarely found in the literature other than for the psychedelics. Animal research has shown that 5-HT2A receptor activation plays a role in normal neuropsychological and memory functioning –. Another explanation for the present results has to do with motivation. There is evidence that motivation may in fact improve performance of drug users in neuropsychological tasks . While the recruited ayahuasca users may have been motivated to demonstrate the safety of ayahuasca to researchers, the controls did not obtain any specific benefit from their participation in the study.
Concerning the capacity of the Frontal Systems Behaviour Scales, a self-report questionnaire, to detect impairment, it is worth noting that it has revealed deficits in non-addicted  and addicted polydrug users , . The lower scores found for our ayahuasca subjects on this measure of prefrontal deficits is consistent with their better neuropsychological performance. This result was found for both samples in the first assessment and in the second.
4. Life Attitude and Psychosocial Well-beingAll SOI scores were consistently higher in both samples and along time for the ayahuasca users, in consonance with scores on the Self-Transcendence subscale of the TCI. Although a recent study showed no significant differences in spiritually after an ayahuasca session, the magnitude of the observed change was positively correlated with the intensity of the peak of the experience . The qualitative data recorded revealed common spiritual themes among participants . In our first assessment, ayahuasca users showed higher scores on Purpose in Life, although this finding was not replicated one year later. This difference in Purpose of Life may be understood as a consequence of the religious use of ayahuasca, and is compatible with adherence to a religious belief . In line with the above results, ayahuasca users scored higher on subjective psychological well-being. In a previous report where these same participants were assessed on frequency and degree of illicit drug use, ayahuasca users scored lower on the different dimensions of the Addition Severity Index (ASI; ). Taken together, the data point at better general mental health and bio-psycho-social adaptation in the ayahuasca-using group compared to the control subjects.
The Spiritual Orientation Inventory (SOI)In the first assessment, ayahuasca users showed significantly higher scores on all 9 components of the SOI, as revealed by a main Group effect on Transcendent Dimension [F(1,216) = 153.54; p<0.001], Meaning and Purpose in Life [F(1,216) = 78.44; p<0.001], Mission in Life [F(1,216) = 76.62; p<0.001], Sacredness of Life [F(1,216) = 30.14; p<0.001], Material Values [F(1,216) = 66.78; p<0.001], Altruism [F(1,216) = 19.32; p<0.001], Idealism [F(1,216) = 25.59; p<0.001], Awareness of the Tragic [F(1,216) = 48.64; p<0.001], and Fruits of Spirituality [F(1,216) = 91.03; p<0.001]. A significant Group by Sample interaction was found for the latter dimension [F(1,216) = 4.45; p = 0.036], with differences between users and controls being larger in the Urban sample than in the Jungle sample.
In the second assessment, the pattern of results remained unchanged, with higher scores on all components in the ayahuasca-using subjects. Thus, significant Group effects were found on Transcendent Dimension [F(1,112) = 73.68; p<0.001], Meaning and Purpose in Life [F(1,112) = 33.88; p<0.001], Mission in Life [F(1,112) = 38.56; p<0.001], Sacredness of Life [F(1,112) = 38.83; p<0.001], Material Values [F(1,112) = 21.82; p<0.001], Altruism [F(1,112) = 5.02; p = 0.027], Idealism [F(1,112) = 7.33; p = 0.008], Awareness of the Tragic [F(1,112) = 16.36; p<0.001], and Fruits of Spirituality [F(1,112) = 44.01; p<0.001].