There is no authoritative information on how long the hypothyroid phase of subacute thyroiditis lasts, but it may generally be 6 to 8 weeks, depending on the individual, and it may develop into permanent hypothyroidism. Subacute thyroiditis has a thyrotoxic phase, a hypothyroid phase, and a recovery phase. There is no authoritative information on how long the hypothyroid phase of subacute thyroiditis lasts. Generally, it may last 6 to 8 weeks, however, due to the different conditions of each patient, the exact time can not be generalized, and there is obvious individual variability. In addition, a small number of patients with subacute thyroiditis may also have a chance of developing permanent hypothyroidism, which may not necessarily transition to the recovery phase, mainly because of the significant destruction of thyroid tissue. Patients need to actively cooperate with their doctors, follow up regularly, and closely monitor changes in their condition. Patients with subacute thyroiditis in the hypothyroidism stage need to go to the hospital in time for standardized treatment, strengthen daily life management, and review the thyroid function on time.