Ayahuasca is a powerful hallucinogenic tea that has been brewed in the Amazon rainforest for thousands of years. Although the brew’s main active ingredient, dimethyltryptamine (DMT), is illegal in most countries, recent research suggests the drug may have significant therapeutic properties in the context of improving depression and anxiety symptoms. A new study published this week — the largest thus far on ayahuasca — adds weight to this body of evidence.

The Global Ayahuasca Project was conducted between 2017 and 2020 and involved more than 11,000 individuals, 7,785 of whom suffered from symptoms of depression or anxiety at the time they took the drug. The participants had to fill an online self-reported questionnaire designed to measure mental health outcomes among Ayahuasca users.

The results were impressive, to say the least. Nearly 94% of the respondents experienced at least some sort of improvement in their depression symptoms, ranging from “a bit” and “great” to the complete resolution of their depression. The same was reported in 90% of cases for anxiety symptoms.

Users who reported profound mystical experiences tended to report the greatest improvements in their depression or anxiety symptoms. Similarly, insights into one’s personal relationships following Ayahuasca use were also correlated with improved mental health outcomes.

However, a small fraction actually saw their mental health deteriorate following Ayahuasca use. About 2.7% of respondents reported worsened depression symptoms and 4.4% reported worsened anxiety symptoms. The researchers found that feeling lonely, nervous, anxious or on edge, as well as depressed or hopeless in the weeks immediately following Ayahuasca consumption were predictors of worsened symptoms.

“Drinkers of Ayahuasca in naturalistic settings perceived remarkable benefits for their affective symptoms in this survey assessment. There is no obvious evidence of negative mental health effects being associated with long-term consumption. Additional randomized controlled trial evidence is required to establish the efficacy of Ayahuasca in affective disorders, and to understand the worsened symptoms reported by a small percentage of drinkers,” the authors of the study wrote in the Journal of Affective Disorders Reports.

The fact that this cross-sectional study relied on self-reported data is an important limitation. Also, the study relied on reaching out to Ayahuasca users on niche forums and websites, where individuals with positive experiences are more likely to be online and respond, thus contributing to selection bias to some degree. However, the very large sample size makes it a valuable study. It’s not alone either.

Ayahuasca and mental health

Traditionally, ayahuasca is made by brewing the Banisteriopsis caapi vine and the Psychotria viridis shrub, along with other native plants, in a specific manner. When ingested, the brew delivers a powerful dose of DMT to the body. Typically, a DMT trip shouldn’t last more than a couple of minutes but thanks to the presence of at least one monoamine oxidase-inhibiting plant, the DMT can bind to receptors in the brain for hours. The experience has been described as anything between enlightening to downright distressing.

The brew contains several substances that alter brain chemistry. Among them, some regulate the neurotransmitters serotonin and MAO-A. It was also previously shown that ayahuasca directly affects activity in the hippocampus and amygdala, areas of the brain responsible for memory and emotions, respectively.

A 2013 study carried out by researchers led by Gerald Thomas from the University of Victoria in Canada, found that ayahuasca therapy causes significant improvements “for scales assessing hopefulness, empowerment, mindfulness, and quality of life meaning and outlook subscales.” Thomas argues that ayahuasca therapy is particularly helpful for those suffering from psychological trauma, which puts them at risk of developing alcohol and other drug addictions.

A study published in 2020 by neuroscientists at the University of California, San Francisco, scanned the brains of 50 healthy participants the day before and after they received either a single low dose of Ayahuasca or a placebo. According to the researchers, “the psychedelic experience induced by ayahuasca has a long-lasting effect on the functional organization of brain networks supporting higher-order cognitive and affective functions.”

Changes in these neural networks are associated with introspection, altered levels of affect, and motivation, which may explain both the altered states of consciousness during the high of the drug and the long-lasting brain changes elicited by ayahuasca.

As Ayahuasca’s potential medical benefits surface, scientists will hopefully be allowed to perform clinical trials with the drug. Decades after it was banned from research by governments, studies may show that Ayahuasca’s benefits far-outweigh its risks in a controlled medical context.