The human heart pumps blood at a certain rate, which creates blood pressure in the arteries. High blood pressure occurs when the heart must pump harder because of stress or something clogging the system. The blood vessels may also constrict because of an imbalance of chemicals in the body. Antihypertensives, or high blood pressure medications, relax blood vessels, reduce the amount of fluid in the body and control the heartbeat.
Postural Hypotension
One of the most common side effects associated with starting an antihypertensive drug treatment occurs because the body needs time to adjust to having a lower blood pressure. Prior to the use of such drugs, the high blood pressure appears normal to the rest of the body. When antihypertensives begin to work, the blood pressure drops down to a closer to normal level, but the body does not adjust immediately. The result, known as postural hypotension, causes lightheadedness and dizziness, as well as a feeling of faintness when the person stands up or rises from bending over. Drugs.com classifies this as a non-serious common side effect of many high blood pressure medications. The organization recommends consulting a medical professional if it feels severe--such as actually fainting--or if it does not end on its own. With some medications, such as ACE inhibitors, the side effect classifies as serious and common, and requires medical attention.
Diarrhea and Constipation
Diarrhea occurs commonly with many antihypertensive medicines, as well as other types of drugs, during the beginning of treatment. Diarrhea produces watery bowel movements, often along with cramps in the abdomen. Conversely, some antihypertensives may cause a blockage in the intestines, resulting in constipation. This occurs more commonly with diuretics because they work to rid the body of excess fluid. In either case, the conditions should cease on their own, Drugs.com reports.
Headaches
As the body adjusts to having a new drug in the system, the person may experience headaches. This non-serious common side effect may occur because of a temporary fluctuation of blood pressure as the body acclimates to the medicine.
Blurry Vision
Vision may become blurry for a short time when starting the medication, particularly diuretics. This happens commonly because the drugs change the fluid levels in the body, including the eyes. Eyes need a certain pressure of fluid to focus properly. When not enough liquid exists in the eyes, vision becomes blurry. When the body reaches balance, vision generally clears.
