The timely insulin administration can promptly normalize the blood glucose level. Indications for early insulin therapy include severe insulin deficiency, often in young patients with low body weight; elderly people with sarcopenia and chronic infections; early manifestation of microvascular complications; insufficient effectiveness of two- or three-component combinations of anti-diabetic drugs; severe symptoms associated with hyperglycemia. Adequate insulin therapy reduces lipo- and glucotoxicity, protects beta cells, other tissues and organs from damage. At the same time, there is an opinion that, in view of adverse effects of exogenous insulin and appearance of new anti-diabetic drugs, the insulin therapy should be started as late as possible. Adverse effects include the risk of hypoglycemia, weight gain and possibly also cardiovascular complications. Combinations of insulin with other hypoglycemic drugs are discussed. There is a tendency for the target glycemic levels to increase with age. Obviously, the approach must be individual, taking into account the age, clinical and laboratory data, comorbidities and preferences of patients. Hyperinsulinemia itself can contribute to dyslipidemia and atherosclerosis. Severe hyperglycemia and other adverse effects are more likely with inadequate insulin therapy. In particular, weight gain is possible with long-acting and short-acting insulin mixtures. Correlation of the glucose-lowering effect of exogenous insulin with an increase in body weight was noted. In turn, severe hypoglycemia is associated with major adverse cardiovascular events, arrhythmias, and other complications. Finally, insulin therapy comes with a number of inconveniences, especially for older patients.