What Causes Low Blood Pressure?

Many things can make your blood pressure too low. These range in severity from normal changes caused by pregnancy to dangerous underlying conditions, like heart problems or hormone disturbances. Some low blood pressure causes are simple cases of dehydration brought on by vomiting, intense exercise, or the overuse of diuretics. Some studies have shown that a dehydration-induced weight loss of 1 percent is enough to trigger dizziness, confusion, or other symptoms of low blood pressure.

One especially important cause of low blood pressure is orthostatic hypotension, which is sometimes referred to as postural hypotension. This happens when blood pressure drops rapidly during changes to body position--usually when changing from sitting to standing--inducing classic signs that the blood pressure is too low, like dizziness, blurry vision, and fainting.

Other important causes of low blood pressure include:

• Heart problems that cause low heart rate, diminished heart strength, or a decrease in the amount of blood supplied to the body
• Normal changes associated with the first and second trimesters of pregnancy
• Side effects from certain medications, especially diuretics or other high blood pressure medications, like beta blockers. Medicines used to treat erectile dysfunction and certain psychiatric disorders can also cause low blood pressure.
• Hormone problems such as adrenal insufficiency or thyroid disease (overactive or underactive thyroid)
• Problems with the nervous system--especially disorders of the autonomic nervous system, including POTS and vasovagal syncope--can cause low blood pressure after extended periods of standing.
• Deficiencies of essential nutrients, such as folic acid, can cause the number of red blood cells to decrease (anemia)
• Alterations in blood sugar, like those caused by diabetes
• Age: Some older patients, especially those with existing high blood pressure, can experience postprandial hypotension, where the blood pressure drops suddenly after eating a large meal

While most cases of low blood pressure are not considered medical problems, cases where the low blood pressure is accompanied by symptoms should always be evaluated by a physician. A complete medical workup will often be needed in order to rule out the possibility of an underlying disorder.