Long-term use of ayahuasca, a psychedelic drink used medicinally by indigenous Amazon tribes, may have the potential to serve as the basis for treatments for anxiety disorders, according to a study on fear reactions in rats published in the journal PLoS ONE.

Ayahuasca has traditionally been used in healing ceremonies, and altered emotional states and sensory hallucinations. It is brewed from the vine of the caapi plant, along with a mixture of other native Amazon plants. Chemical analysis shows that the drink contains compounds affecting brain systems related to regulation of the neurotransmitters serotonin and MAO-A. It has also been shown to affect activity in the hippocampus and amygdala in rats, areas of the brain related to memory and emotion.

A team of scientists led by Vanesa Favaro, of the Universidade Federal de São Paulo, conducted a series of studies aimed at determining whether the neural effects ayahuasca led to behavioral changes related to anxiety. Forty-six rats were divided into four experimental groups. Three groups received different doses of ayahuasca, and the fourth group received a placebo. Ayahuasca was administered daily for a period of 30 days. The rats were trained to complete two different types of mazes.

They then were exposed to a fear conditioning procedure, in which they learned to associate a noise with receiving electric shocks. Fear was assessed by the time the rats froze their movements after later being separately exposed to the chamber where they received the shocks (contextual fear) and the noise that accompanied them (tone fear).

The rats who received the lowest dose of ayahuasca froze longer than those in the placebo group after being placed in the contextual fear condition, but not after hearing the tone. This reaction suggests that the rats’ emotional memory formation process was affected by certain levels of ayahuasca exposure. Ayahuasca did not affect rats’ ability to learn and remember how to complete the mazes.

The study authors conclude that, when used repeatedly, ayahuasca alters brain chemistry in ways that may affect certain types memory related to emotional content, but does not have the same impact on other types of memory. Specifically, ayahuasca appeared to strengthen memories of the context in which fear was experienced. Although applications of these findings in humans remain years away, the authors suggest that they may one day help to develop treatments for anxiety-related disorders and other conditions in which memory and emotion play an important role.