The onset of action of antihypertensive drugs mainly depends on the type of antihypertensive drugs changed, and antihypertensive drugs can generally be categorized into short-acting preparations, medium-acting preparations and long-acting preparations in the clinic. 1. Short-acting antihypertensive drugs, such as nifedipine tablets, have a fast onset of action and take effect half an hour after switching to oral administration. Therefore, patients should closely observe the change of blood pressure when switching. 2. Medium-acting antihypertensive drugs: such as nifedipine extended-release tablets and enalapril, etc., it takes a period of time for their effects to take effect after switching to oral intake, and they gradually take effect after thirty minutes, and their antihypertensive effect will be maximized after taking them for four to six hours, and then their antihypertensive effect will be weakened gradually with the passage of time. 3. Long-acting antihypertensive drugs: such as amlodipine and irbesartan tablets, which have a long duration of action, slowly take effect within 24 hours, but to maximize the effect, it may take 3 to 4 days or even more than a week. Long-acting antihypertensive drugs are more effective, although they work slowly. Patients with hypertension should monitor their blood pressure frequently after switching medications. You may choose to measure your blood pressure once a day in the morning and once in the evening to see the overall control of your blood pressure as well as to record fluctuations and observe the effectiveness of the treatment. If you need to change your hypertension medication, please use it under the guidance of a specialist.