High blood pressure in the morning and low blood pressure at noon is generally due to changes in the excitability of the sympathetic and parasympathetic nerves. Human blood pressure fluctuates and is regulated throughout the day according to the biological clock, with normal blood pressure being systolic blood pressure <120mmHg and diastolic blood pressure <80mmHg. In the morning, sympathetic excitability rises and blood pressure rises, which is known as the "morning peak phenomenon". At midday, the sympathetic and parasympathetic nerves are in a state of equilibrium, so the blood pressure is lower than in the morning. In the evening, sympathetic excitability is suppressed and blood pressure is low. Therefore, it is normal for blood pressure to fluctuate within the normal range. If the higher blood pressure in the morning and lower blood pressure in the middle of the day is caused by taking antihypertensive medication, it is recommended to seek medical attention for further adjustment of the treatment program. Medication for high blood pressure should be administered strictly according to the doctor's instructions. If large fluctuations in blood pressure are found within a day or accompanied by physical discomfort, immediate medical attention should be sought.