Trace elements are the metals of life, their deficiency and excess in the body lead to metabolic disorders, which cause inhibition of growth and development of the body, a decrease in the intensity of digestive processes, and a disorder of the reproductive system function. Of particular importance are the trace elements selenium, iron, and iodine. Deficiency of a complex of trace elements (selenium, iron, zinc, and iodine) negatively affects all types of metabolism (protein, carbohydrate, lipid, etc.), and has adverse effects on health. This scientific work reveals in detail the biological role of iodine, selenium, and iron describes their significance for the human body, and also lists the main consequences of a shortage or overabundance of these trace elements in the body. In addition, the characteristics of the new drug SIF-Complex - a complex of iodine, iron, and selenium are given, and its main physico-chemical parameters are described. The new drug is being tested for acute toxicity, chemical toxicity, and irritant effect on white mice, white rats, and rabbits. The dynamics of the body weight of animals and their condition are monitored. Studies of rat blood and the condition of their internal organs were carried out. Conclusions are made about the low toxicity of the drug.