Tachykinin neuropeptides play a crucial role in the neurohu- moral regulation of visceral functions; however, the nature of their influence on the fine mechanisms of bile acid biosynthesis requires further clarification. The study aimed to establish non-linear dose-dependent patterns of the effect of substance P on choleresis dynamics and to conduct an analysis of specific bile acid fractions to identify their biosynthetic pathways in hepatocytes and enterohepatic transport. The study was con- ducted on 56 non-linear male white rats (weighing 200–250 g) under subperitoneal administration of substance P at doses of 0.1, 1.0, and 10.0 µg/100 g of body weight. The volumetric rate of choleresis and the relative biochemical composition of bile were evaluated using thin-layer chromatography followed by densitometry. The bile acid output, as well as conjugation and hydroxylation coefficients, were calculated. It was established that substance P exerts a differentiated effect on the secretory activity of the liver depending on the dose. The most pronounced hypercholeretic effect and activation of conjugating enzyme systems (increased output of tauro- and glycocholates) were observed at a dose of 1.0 µg/100 g. In contrast, the use of extreme doses (0.1 and 10.0 µg/100 g) revealed a decrease in conjugation and hydroxylation co- efficients, suggesting a metabolic switch towards the de novo synthesis of free cholates. The results expand current understanding of the role of tachykinins in the regulation of liver bile formation, particularly regarding the switching of bile acid biosynthetic pathways, changes in their conjugation coefficients, and the specifics of receptor-mediated regulation of choleresis under conditions of prolonged crisis and stress states, especially those accompanied by pain.