This study isolated three indole monoterpene alkaloids, lyaloside, naucletine, and strictosamide, from the leaves of Psychotria suterella Mull. Arg. (Rubiaceae), which had not been previously reported for the genus. The leaves were dried, ground, and extracted with EtOH containing 5% NH₄OH, followed by classical acid/base extraction, column chromatography (CC), vacuum liquid chromatography (VLC), and semi-preparative HPLC for separation and purification. The structures were identified using 1D/2D-NMR, optical rotation measurement, and HPLC. These alkaloids were not found in the roots, seedling-derived root cultures, or leaf-derived callus cultures of P. suterella. Tail flick tests showed no significant analgesic effect of the leaf alkaloid extract (100 and 300 mg/kg) or lyaloside (10 or 30 mg/kg); high doses of the total alkaloid extract caused convulsions and death, while the highest dose of lyaloside had similar but less severe effects. Chemotaxonomic analysis indicated that these alkaloids suggest P. suterella has a Rubiaceae-typical biosynthetic route (atypical for Psychotria) and can serve as chemotaxonomic markers to clarify the genus's boundaries.