Ayahuasca is commonly used by indigenous communities in healing ceremonies in the Amazon rainforest. It's a tea that produces hallucinatory effects after consumed.
There have been several studies done on ayahuasca, but most usually with an incredibly small a sample size. There aren't that many in overall scientific literature, but the ones that do exist seem to be optimistic about ayahuasca's ability to treat mental health issues.
Scientific American: Ayahuasca Psychedelic Tested for Depression
BBC: Why do people take ayahuasca?
LiveScience: Ayahuasca: Psychedelic Tea from the Amazon