Eat two four tablets of antihypertensive drugs blood pressure within a day, high and low, the reasons include blood concentration, onset of action time, blood pressure fluctuation pattern. 1. Blood concentration: After the antihypertensive drug enters the body, it is not possible to reach the blood pressure concentration immediately so as to reduce the blood pressure, but it needs a period of time to accumulate to the concentration that can play a role. 2. Onset of action time: different antihypertensive drugs have different onset of action time, short-acting antihypertensive drugs have fast onset of action time, for example, nifedipine controlled-release tablets; some drugs are long-acting antihypertensive drugs, for example, amlodipine benzenesulfonate tablets and so on. 3. The law of blood pressure fluctuation: blood pressure is in dynamic fluctuation, there are two physiological peaks in a day. Blood pressure is in dynamic fluctuation, to monitor blood pressure, regular visits to the hospital to adjust the medication to control blood pressure.