"Junk food" is very popular worldwide. Its taste requires various food additives, the most common of which is monosodium glutamate. Many authors describe functional and structure changes in the nervous, digestive, immune, respiratory and sexual systems that may be caused by monosodium glutamate. Therefore, the purpose of the study is to elucidate the mechanism of its actions on organs and systems. There has been suggested that monosodium glutamate mediates the phenomena of nervous cell apoptosis and acts as a powerful neurotoxin. Studies on rats demonstrated that the diet rich in monosodium glutamate created the preconditions for the development of epilepsy, disorders of emotional and adaptive reactions, hyperalgesia. Monosodium glutamate induced pronounced histological changes in the organs of the gastrointestinal tract, up to the manifestation of acute pancreatitis. Monosodium glutamate causes a destructive effect on the immune system as well. There was an increase in lymphocytes number that were destroyed by apoptosis, narrowing of the vascular lumens in the spleen, dilation of the venous lumen and blood supply in the lymph nodes. The effect on the respiratory system is remaining ambiguous. Atelectasis and pulmonary emphysema, fibrosis, oedema, and haemorrhage up to brown indurations have been reported under the monosodium glutamate consumption in animals. The negative effects of monosodium glutamate potentiated by smoking caused the activation of lipid peroxidation and protein oxidative modification. Monosodium glutamate caused sexual dysfunction in experimental rats that was also likely associated with hypothalamic damage, oxidative stress, and hormonal mechanisms. Thus, monosodium glutamate has been proven to produce a systemic effect on humans and animals. This food supplement has a complex mechanism of action, which can be indirect and direct. The indirect effects deteriorate normal functioning of target organs of the hypothalamus hormones, impacts the autonomic nervous system. The direct effects contribute to hypoxia and fibrosis in the organs, dysfunction of histohematological barriers and haemorrhages.