Recently, I posted a couple studies on Twitter which suggested long-term ayahuasca use increased intelligence.
Ayahuasca brew is a very strong psychedelic produced by combining N,N-dimethyltryptamine (colloquially called DMT, not 5-MEO-DMT) and an MAOI, ayahuasca vine, or Banisteriopsis caapi. It has a strong history in South American religions and tribes for ritual/shamanic use. Its effects are similar to that of DMT, though lasting much longer, typically 8-12 hours, compared to 5-20 minutes for a DMT trip (See Smith, 2017 for a comparison of the two drugs).
The link between psychedelics and intelligence is certainly plausible. Ly et al. (2018) found “that psychedelic compounds such as LSD, DMT, and DOI increase dendritic arbor complexity, promote dendritic spine growth, and stimulate synapse formation.” They also find that psychedelics increased connectivity between neurons. Dakic et al. (2016) found that the MAOI part of ayahuasca may stimulate the growth of new brain cells.
Fischer et al. (1970) found that even a small dose of psilocybin resulted in greater ability to identify when two parallel lines converged, but it wasn’t tested if this effect persisted in the long term. (This has been used in convergence with other evidence of McKenna’s ‘stoned ape’ theory, part of which is that psilocybin is responsible for a massive brain size increase ending 100,000 years ago, and responsible for the change in cultural complexity and language. Personally, I’m not the biggest fan of McKenna and his views, though Paul Stamets, who I respect a lot more, seems convinced of this theory as well, so who knows? Maybe it has some truth.)
I have previously argued that intelligence and creativity are fairly similar traits, despite their low correlation (Jeffrey, 2019). Psychedelics seem to permanently increase creativity. Harman et al. (1966) experimentally studied a group of engineers, architects, physicists, etc., giving some of them mescaline and leaving the rest without. The employees given mescaline, experienced not only greater creative-problem-solving ability during the session, but also during the subsequent weeks following the trip. Fadiman (2011) summarizes the long-term results of the study, stating,
“Pragmatic Utility of Solutions. The practical value of obtained solutions is a check against subjective reports of accomplishment which might be attributable to temporary euphoria. The nature of these solutions was varied; they included: (1) a new approach to the design of a vibratory microtome, (2) a commercial building design accepted by client. (3) space probe experiments devised to measure solar properties, (4) design of a linear electron accelerator beam-steering device, (5) engineering improvement to magnetic tape recorder, (6) a chair design modeled and accepted by manufacturer, (7) a letterhead design approved by customer, (8) a mathematical theorem regarding NOR-gate circuits, (9) completion of a furniture line design, (10) a new conceptual model of a photon which was found useful [in the future], and (11) design of a private dwelling approved by the client.” (p. 132)
The main argument to the contrary would be that Pokorny et al. (2019) found that LSD impaired working memory. Working memory is strongly related to g, but that doesn’t mean LSD is affecting the g portion. The same study states,
“Regression analyses to predict LSD-induced cognitive impairments testing the impact of subjective effects and IQ were not significant. Importantly, this suggests that cognitive processes under
LSD are not confounded by psychedelic effects, in particular visual inaccuracies or disturbances. Furthermore, LSD-induced
impairments were not related to individuals’ IQ, suggesting that
5-HT2A receptor stimulation by LSD impaired working memory
and executive functions independently of general intelligence.”
So, the evidence that psychedelics impair mental ability is quite slim.
The studies I cited in my tweet were Bouso et al. (2012) and Bouso et al. (2015). The first study used three intelligence tests: the Stroop test, the Wisconsin Card Sorting Test and the Letter-Number-Sequencing from the Wechsler’s tests. They had two ayahuasca-using groups and two groups which rarely used ayahuasca, one of each was from a jungle sample and one of each was an urban sample. In two separate assessments, the ayahuasca groups scored better than the control groups on all three tests.
Maybe the effects aren’t on g. The second study used two groups: one which used ayahuasca long-term, and the other which did not. The groups were matched for age, sex, years of education, verbal IQ and fluid IQ. Regardless, the long-term ayahuasca group had improved reaction times compared to the control group. To further solidify this theory, one could do a study using the method of correlated vectors, but overall, it seems that long-term ayahuasca usage improves general intelligence or g. Bouso et al. (2013) also found an improvement in reaction times for long-term ayahuasca users.
One of the oldest studies on psychedelics and IQ I could find was done by Levine et al. (1955). This study did find a decrease in IQ from usage of LSD. However, it suffered a number of issues: range restriction, a flaw in the control method, as well as a very small sample. Nonetheless, it’s there. Conversely, Kurland et al. (1971) used multiple intelligence tests and found that an LSD trip significantly increased scores on all of them.
These effects go beyond the realm of the general population. In reviewing the evidence of usage of psychedelics for mentally disturbed children, Rhead (1977) states,
“Although Dr. Bender and her colleagues were originally interested in the possibility that the psychedelic effects of LSD might “break through the autistic defenses of severely schizophrenic children” (Bender 1966), they soon became more intrigued by the effects on the autonomic nervous system of repeated administrations. It seemed that regular administration tended to normalize the plasticity and lack of maturation noted above, resulting in improved reality contact, a reduction in the reporting of bizarre fantasies and preoccupations, weight gain, improved gastrointestinal regulation, normalization of sleep patterns, increased scores on the Vineland Social Maturity Scale, a rise in IQ on the WISC (Wechsler Intelligence Scale for Children), normalization of the blood pressure response to epinephrine injectio n, improved comprehension of speech, reduction in stereotyped motor play, lower anxiety, and elimination of the need for tranquilizing, antidepressant and sedative medication which most of the children had been taking prior to treatment with LSD. Although most of these results were described for various subsarnples of the entire population studied, and the studies generally lacked controlled designs and statistical analyses of the data, nevertheless one could certainly consider their results to be promising.”
People given a dosage of psilocybin were able to better solve matrix problems for at least a week after the dose was given (Mason et al., 2019). This implies a lasting increase in intelligence after dosing. Prochazkova et al. (2018) found that, after a microdose of psilocybin, convergent and divergent thinking processes were improved, but scores on a short version of the Raven’s test (measuring fluid intelligence) were not. Other studies have been done using the Raven’s Progressive Matrices test. One very early study was done using MDA, which is similar to MDMA, but retains some elements of LSD-type visuals. Using a very large sample, it was found that MDA statistically significantly increased post-“trip” scores on the Raven’s Progressive Matrices (Yensen, 1949).
Not a psychedelic, but Lion’s Mane, an entirely legal edible fungus, also appears to increase IQ (Davis, 2017). Similar to psychedelics, Lion’s Mane promotes neural growth and restoration. This further leads me to believe psychedelics increase IQ primarily through their neurogenesis-like effect.