AbstractIntroductionTetrapterys mucronata Cav. (Malpighiaceae) is a plant used in some regions of Brazil in the preparation of ayahuasca.ObjectiveTo determine the content of the main tryptamine alkaloids in the stem bark of T. mucronata Cav. and assess their possible toxic and hallucinogenic properties based on the doses found in a water decoction that mimics the ayahuasca preparation.MethodsFour alkaloids previously described for their toxic and hallucinogenic properties were quantitated by multiple reaction monitoring HPLC combined with electrospray ionisation and tandem MS (HPLC–ESI/MS/MS) in the water decoction and ethanolic extracts from the bark of T. mucronata.ResultsExhaustive extraction of the stem barks with ethanol revealed the following alkaloid levels: bufotenine (1) 3.26 ± 0.31 mg/g, 5‐methoxy‐N‐methyltryptamine (2) 0.88 ± 0.08 mg/g, 5‐methoxy‐bufotenine (3) 3.07 ± 0.22 mg/g and 2‐methyl‐6‐methoxy‐1,2,3,4‐tetrahydro‐β‐carboline (4) 0.14 ± 0.004 mg/g. The water decoction presented slightly lower levels, ranging between 2.32 ± 0.14, 0.50 ± 0.04, 1.53 ± 0.09 and 0.10 ± 0.01 mg/g for (1), (2), (3) and (4) respectively.ConclusionsThe HPLC–ESI/MS/MS quantitation revealed significant alkaloid levels, in particular for bufotenine and 5‐methoxy‐bufotenine. As such compounds are known for their toxic and hallucinogenic properties, these results indicate that the consumption of this plant as an ingredient in ayahuasca preparations may present a risk to consumers. Copyright © 2015 John Wiley & Sons, Ltd.