There appears to be little reason to believe that ayahuasca is either addictive or dangerous in any conventional sense. A well-publicized psychiatric study of members of the União do Vegetal, an ayahuasca-using new religious movement that originated in Brazil, showed significant differences between long-term members of the UDV who consumed ayahuasca at least two times a month in religious rituals, compared with demographically matched controls who had never consumed ayahuasca. As we have discussed, personality testing instruments showed UDV members to be more reflective, rigid, loyal, stoic, slow-tempered, frugal, orderly, and persistent, and with higher scores on measures of social desirability and emotional maturity than the controls.
The ayahuasca-using participants also differed from the controls in being more confident, relaxed, optimistic, carefree, uninhibited, outgoing, and energetic, and with higher scores on traits of hyperthymia, cheerfulness, stubbornness, and overconfidence. Significantly, on neuropsychological testing the UDV group demonstrated significantly higher scores on measures of concentration and short-term memory, despite the fact that many ayahuasca users reported significant psychiatric and substance abuse histories prior to their church membership.
Now, there are certainly some problems with this study. UDV worship is a structured and stable environment. Participants remain seated, with long periods of silence during which they seek self-knowledge through mental concentration, aided by ayahuasca. The ayahuasca-using participants had to have been members of UDV for at least ten years, with at least twice-monthly — that is, highly regular — attendance at these services. Thus, the ayahuasca users may have been preselected for personality traits of stability, persistence, and orderliness; self-reports of prior mental health problems by church converts may be viewed with some level of skepticism.
Moreover, while subjects and controls were matched for age, ethnicity, marital status, and level of education, there was apparently no attempt made to control for regular churchgoing, a measure on which the ayahuasca users were preselected for perfect scores, and which may well be correlated with personality traits for which they also scored high. Still, the study certainly gave no grounds to believe that long-term UDV church membership, along with concomitant twice-monthly drinking of ayahuasca, had caused any significant personality or cognitive detriment to its members.
Still, there is reason to be cautious when using any powerfully psychoactive plant. A letter published in the December 2008 issue of the British Journal of Psychiatry, signed by Rafael G. dos Santos of the Interdisciplinary Group for Psychoactive Studies, Brazil, and the well-known DMT researcher Rick J. Strassman — see here and here — of the University of New Mexico School of Medicine, reports the case of a young man who suffered two psychotic episodes, a year part, during and after participation in ayahuasca ceremonies. Before the first episode, he had already used ayahuasca "more or less twice per month, for about two years," sometimes using marijuana concurrently, without incident.
During one particular ayahuasca ritual, he again combined its use with marijuana and experienced very intense paranoid and suicidal ideas – "these people are going to kill me in order to make me a human sacrifice;" "I will be operated upon and they will open my body;" "I have sinned and the spirits are persecuting me;" "I should kill myself right now before they do." These feelings were so intense that he superficially cut himself with a sharp-edged ceremonial item during the ayahuasca ritual.
Symptoms persisted for two to three weeks and resolved after treatment with risperidone, an atypical antipsychotic medication. After being treated for a year, he resumed attending ayahuasca ceremonies; during the third of these ceremonies, while not using marijuana, he again experienced similar paranoid and suicidal ideation, which persisted for another two to three weeks, and which again responded to risperidone treatment over the next year.
It is hard to know what to make of this. At the time of the first episode, neither the young man nor his parents had a history of psychosis. He had consumed other hallucinogens on multiple occasions, and had been a nearly-daily marijuana smoker for the preceding six years with no significant adverse effects. Before the first episode, he had already used ayahuasca "more or less twice per month, for about two years," sometimes using marijuana concurrently, without incident. Because of the concurrent use of marijuana with ayahuasca, it is likely that the ceremony was that of the Centro Eclético de Fluente Luz Universal Raimundo Irineu Serra branch of the Santo Daime church, but it is difficult to know whether this has any relevance.
The authors conclude: "Given the low incidence of, but potentially high morbidity associated with, transient drug-induced psychosis, both research and religious use of ayahuasca should be contraindicated in people with a history of psychosis."