Peganum harmala L. is a medicinal plant from the Mediterranean region and Asia currently used for recreative psychoactive purposes (Ayahuasca analogue), and increasingly involved in toxic cases. Its psychopharmacological and toxicological properties are attributed to quinazoline and b-carboline alkaloids. In this work three major quinazoline alkaloids were isolated from P. harmala extracts and characterized as peganine (vasicine), deoxypeganine (deoxyvasicine) and a novel compound identified by HPLC-DAD-MS and NMR as peganine b-D-glucopyranosyl-(1 / 6)-b-D-glucopyranoside (peganine glycoside). Peganine appeared in flowers and leaves in high levels; high amounts of deoxypeganine and peganine were found in immature and green fruits whereas peganine and peganine glycoside accumulated in high amount in dry seeds reaching up to 1 and 3.9% (w/w), respectively. Roots and stems contained low amount of quinazolines. Seeds extracts containing both quinazoline and b-carboline alkaloids potently inhibited human monoamine oxidase (MAO)-A. However, quinazoline alkaloids did not contribute to MAO inhibition that was due to b-carbolines, suggesting that MAO-related psychoactive or toxic actions do not arise from quinazolines. Quinazoline alkaloids were poor radical scavengers in the ABTS assay whereas seed extracts had good activity. Quinazoline alkaloids are known to exert bronchodilator and abortifacient actions, and could contribute to such effects reported in P. harmala.