How long does it take for high hemoglobin to return to normal is related to the cause of the disease. Those caused by blood concentration can be reduced to normal after removing the cause of the disease, those caused by strenuous exercise can be lowered after drinking water, chronic obstructive pulmonary disease can be gradually reduced by improving the hypoxia and treating the primary disease, and true erythrocytosis can be lowered by hydroxyurea and blood-letting therapy to make hemoglobin lower. There are many reasons for high hemoglobin, but how long it takes for specific high hemoglobin to return to normal is related to the causes of high hemoglobin: 1. Blood concentration: such as heatstroke, massive dehydration, acute gastroenteritis caused by severe vomiting, extensive burns, diarrhea, diabetic ketoacidosis, etc. can be caused by a decrease in blood volume and blood concentration, hemoglobin concentration will be relatively high, generally in the removal of the cause of the gradual decline to normal, usually for 3-5 days. 2. Strenuous exercise: high hemoglobin can also occur, and hemoglobin can be lowered after drinking water. 3. Chronic obstructive pulmonary disease: such as emphysema, pulmonary heart disease, congenital heart disease and other diseases, long-term tissue hypoxia can cause hemoglobin elevation, improve hypoxia and treatment of the original disease hemoglobin concentration can be gradually decreased, the specific time from a few months to 1 or 2 years. 4. True erythrocytosis: oral hydroxyurea, intravenous bloodletting and other treatments can reduce hemoglobin. Specific diagnosis and treatment should be carried out under the guidance of physicians.