Li blood levels in aspirin + Li-treated rats. Rats were fed regular food (control) or Li-containing food [0.1% (LLD-Li), 0.2% (STD-Li)] for 42 days. Low-dose ASA (1 mg/kg, ip) was administered alone or together with Li. Blood was collected on days 0 and 42 of treatment, plasma separated, and Li levels determined as described in Materials and Methods. Li levels were undetectable in all groups on Day 0 and thus are not presented in the Figure. Results are the means ± SEM of a single representative experiment out of two demonstrating a similar pattern with 9–12 rats per group in the depicted experiment. * p < 0.0001 vs. Control, # p < 0.0001 vs. LLD Li. Two-way ANOVA: ASA effect: F1,59 = 0.1849, p = 0.6687; Li effect: F2,59 = 328.6, p < 0.0001; aspirin x Li interaction: F2,59 = 0.1608, p = 0.8519. Post hoc Fisher’s LSD: Control vs. LLD-Li or STD-Li—p < 0.0001, LLD-Li vs. STD-Li—p < 0.0001, LLD-Li vs. LLD-Li + ASA—p = 0.4687, STD-Li vs. STD-Li + ASA—p = 0.9644. Abbreviations: ASA—acetylsalicylic acid, LLD—low-low dose, Li—lithium, STD—standard dose, UD—undetectable.