Experimental and computational studies were performed to determine the antioxidant activities of harmine, harmaline, harmalol, harmane, and 1,2,3,4-tetrahydroharmane-3-carboxylic acid. The in vitro study was conducted using H2O2, ABTS, FRAP and PR tests. The theoretical study was performed using density functional theory (DFT), molecular docking, and molecular dynamics. The in vitro study showed high hydrogen peroxide scavenging activity 27.63 ± 1.74% for harmine which is significantly greater than ascorbic acid (8.02 ± 0.58%). Harmalol has shown the highest antioxidant activity for ABTS, FRAP, and reducing power with 371.15 ± 1.80 µg TE/mg, 11.30 ± 0.01 µg TE/mg, and 671.70 ± 5.11 µg AAE/mg, respectively. DFT analysis indicates that harmalol and harmaline are the most reactive molecules and could scavenge free radicals through the SET-PT mechanism. The docking analysis revealed that harmalol and harmaline have low binding energy and interact through hydrogen and van der Waals bonds with the myeloperoxidase receptor. In addition, molecular dynamics revealed that the protein–ligand equilibrium is stable after 100,000 fs, indicating that harmaline and harmalol could be inhibitors of myeloperoxidase. The obtained results were used to design new harmalol derivative, with promising in silico results. The results of this work showed that harmalol and harmaline have high antioxidant activity in vitro and in silico. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.