The causes of high blood pressure at noon are due to diet, improper rest, primary hypertension, time of taking medication, and secondary hypertension. 1. Diet: If you eat a particularly full meal after lunch, eat too much salt, too greasy food, there will also be a rise in blood pressure at noon. 2. Improper rest: blood pressure is likely to rise at noon after a tiring morning’s work. 3. Primary hypertension: If there is no other disease, and the three blood pressure values measured not on the same day, the systolic blood pressure is ≥140mmHg and/or the diastolic blood pressure is ≥90mmHg, it can be diagnosed as primary hypertension. 4. Antihypertensive drugs: If you take antihypertensive drugs in the morning, the effect of antihypertensive drugs will be weakened at noon, especially there are some short-acting antihypertensive drugs, which will cause the blood pressure to rise at noon. 5. Secondary hypertension: Suffering from hyperthyroidism, kidney disease, adrenal disease, etc. can also trigger hypertension. Suffering from high blood pressure should be timely consultation, drugs should be used under the guidance of physicians.