From the plants of the antidrug medication Heantos 4, 41 alkaloids and 4 other nitrogen containing compounds (1-45) were isolated and structurally identified. Three of them are novel alkaloids, 5-hydroxy-6,7-dimethoxy-3,4dihydroisoquinolin-l(2H)-one (2), thaicanine 4-O-beta-D-glucopyranoside (23), as well as (-)-thaicanine N-oxide (24). Their structures have been elucidated by the mass, NMR spectroscopy and comparison with published data.