In this literature review the authors present the favourable pharmacological effects of milk thistle (Silybum marianum). The medicinal herb has been used since ancient times, primarily because it has liver-protective effects, promo- ters: liver functions and facilitates the regeneration of hepatocytes. The most important active ingredient of milk thistle is silymarin, which is mainly con- centrated in the seed shell. It composed of flavonolignans and flavonoids (70- 80%) and a mixture of polyphenol-like molecules (20-30%) that are not pre- cisely defined chemically. The success of applications at the cellular level is due to the toxin-binding, antioxidant, protein synthesis enhancing, anti-fibrotic, anti-carcinogenic, antiviral and anti-inflammatory effects of the plant's active ingredients. In addition, it can be we" integrated into the treatment of insulin resistance and diabetes, can help miIk production, and has cardio- and neurop- rotective properties. Its beneficial antimicrobial effects in the gut can contribute to the healthy intestinal flora. Most of the biological effects have been proven in vitro. The absorption of active ingredients of the milk thistle is quite low (20- 500/0). Furthermore, after absorption, the hepatic enzymatic biotransformation of silymarin is intense. Thus, the study of in vivo effects is more difficult and much less biological efficacy can be detected compared to in vitro investiga- tions. Diets containing the active ingredients of milk thistle can be used well in the treatment of companion animals. Also, diets of exotic birds, parrots and pigeons may contain milk thistle extract. In racing horses, herb-based cure is often used to prevent stress-induced negative health effects. In the case of ruminants, pig, dog, cat and poultry species, the milk thistle seed, the oil and various by-products produced after oiI-pressing can be mixed in the diet.