We have talked before — here and here — about the Grob, McKenna, Callaway, et al. psychiatric study on the long-term effects of drinking ayahuasca in the ceremonies of the União do Vegetal church. I noted that the study had not clearly disentangled any bias that might have resulted from the fact that the ayahuasca drinkers — but not controls — had been preselected for their orderly churchgoing habits. Here is a study that may shed some light on that question.
The twenty-question Self Report Questionnaire, or SRQ-20, is a screening tool for common mental disorders that investigates nonpsychotic symptoms — depression, anxiety, somatiform disorders — in the month prior to the interview. The questionnaire consists of four questions about physical symptoms and sixteen questions about emotional symptoms, all with yes-no answers — questions about such things as crying, tiredness, and inability to enjoy life. The test was validated in a Brazilian population, and thus is commonly used in South America to identify psychiatric symptoms in a primary care setting.
The higher the number of positive yes responses, the greater the likelihood of psychopathology. The validity study in Brazil reported that a score of more than eight positive responses is an adequate cut-off point to detect nonpsychotic mental disorders. The test was reported to have a sensitivity of 83 percent, a specificity of 80 percent, and both positive and negative predictive values of 82 pecent, which makes the SRQ-20 a pretty good little test.
The chart below should make the results clear. The stacked columns run from zero positive responses on the left to greater than sixteen positive responses on the right — that is, from left to right in order of increasing psychopathology.
The chart clearly shows that Shuar who drank less ayahuasca had higher psychopathology scores on the SRQ-20, and those who drank more ayahuasca had lower psychopathology scores. Put another way, the chart shows Shuar who drink more ayahuasca stacked at the left-hand low-pathology end of the chart, and those who drink less ayahuasca stacked at the right-hand high-pathology end. Of those participants who gave zero positive responses, 72 percent had drunk ayahuasca more than 21 times.
The study also revealed that there appears to be a generally high rate of psychopathology among the Shuar: more than 60 percent of the participants gave eight or more positive responses on the SRQ-20. Fericgla attributes this unusual level to the accelerated process of deculturation that the Shuar were undergoing — the destruction of their traditional way of life, the plundering of their environment by multinational petroleum and lumber companies, territorial conflicts with colonists, the loss of their spiritual values. Even so, the distribution of the high scores is interesting. Of those who gave eight or more positive responses, 72 percent were women, and 35 percent were men. Part of the explanation may be that Shuar women bear the brunt of deculturation more than the men. Another part may be that Shuar men drink ayahuasca at twice the rate of women.
Now, again, what we have here is simply an apparent association between increasing ayahuasca consumption and lower scores on the SRQ-20. The study cannot tell us if there is a causal connection, or, if there is, in which direction it runs. It may be, for example, not that drinking ayahuasca causes better mental health, but rather that people with greater mental health — for any of a variety of reasons — drink more ayahuasca; or even that some third factor — family or social status, for example — is causally related to both.
But the bottom line of this study remains that — consistent with the results of the União do Vegetal study and, indeed, of the long-term study of peyote use we discussed here — there is little evidence that the long-term use of either sacred plant in its ceremonial setting causes any psychological harm, and appears to be associated with mental health benefits.