ESC, FRAX and DAPH, but not SCOP, counteract t-BuOOH—induced reactive oxygen species (ROS) formation in SH-SY5Y cells. Cells were treated for 2 h with various concentrations of the studied coumarins (5–20 µM) and then with t-BuOOH (200 µM) for 30 min. At the end of treatment, ROS formation was determined using the fluorescent probe 2′,7′-dichlorodihydrofluorescein diacetate (DCFH-DA). Data are expressed as fold increases of ROS formation induced by t-BuOOH and reported as mean ± SD of four independent experiments (* p < 0.05, ** p < 0.01 and *** p < 0.001 vs. cells treated with t-BuOOH at one-way ANOVA with Dunnett post-hoc test).