Hypothyroidism does not usually cause hypertension, or even low blood pressure, but hypothyroidism decreases lipid clearance, which can lead to atherosclerosis in the long term, when blood pressure will gradually increase. Hyperthyroidism can cause hypertension, which is characterized by an increase in systolic blood pressure, a decrease in diastolic blood pressure, and an increase in pulse pressure differential. Abnormal thyroid function can lead to unstable blood pressure, which is caused by abnormal secretion of thyroid hormones and dysfunction in blood pressure regulation. In general, hyperthyroidism increases the secretion of thyroid hormones, leading to increased heart rate, sympathetic excitation, and increased cardiac conduction velocity, which can lead to hypertension with a predominantly high systolic blood pressure. For hypertension caused by hyperthyroidism, the blood pressure will return to normal after the hyperthyroidism is controlled through active treatment of the primary disease. In patients with hypothyroidism, blood pressure usually decreases to varying degrees due to reduced heart function, insufficient blood supply to the heart, myocardial ischemia and lack of oxygen, and does not trigger hypertension. However, some hypothyroidism with arteriosclerosis may result in a gradual increase in blood pressure.