The experimental psychosis observed after drinking Hoasca reproduces the pathologic transmethylation theory of schizophrenia. The occurence of DMT in the Hoasca drink and in the urine samples of subjects supports now that the biological and neuropsychological effects are produced by this methylated indolealkylamine assisted by the beta-carboline derivatives. These results further confirm tha tthe urinary hallucinogenic compounds detected in healthy subjects (post-Hoasca, but not before) are the same as those found in the urine samples of acute psychotic unmedicated patients. The ability of Hoasca to modulate serotonergic receptors was evaluated, and thereby to which ecxtent cortisol, prolactin and serotonin levels as well as perceptual and cognitive processes were affected. The degree of Hoasca monoamine oxidase (MAO) inhibition was directly correlated with the concentration of MAO-inhibiting beta-carbolines. The additive combination of harmine and tetrahydroharmine (THH) accounts for the MAO inhibition exhibited by Hoasca.