Magnesium is one of the most abundant trace elements in the body. It is a cofactor for more than 300 enzymes, participates in muscle contraction, in conducting nerve impulses, in building bones. The reduced level of magnesium in the serum leads to increased neuromuscular excitability, tetany, convulsions. Magnesium deficiency develops with insufficient food intake, hypoparathyroidism, hyperthyroidism, prolonged intake of diuretics, in the postoperative period, etc. Prolonged and significant magnesium deficiency can lead to muscle spasms and heart rhythm disorders.