Low blood pressure (hypotension) is a condition in which the force of blood pumping through the arteries is lower than normal.
There is no specific measurement at which blood pressure is considered too low, and it is generally not a cause for concern if a person has no bothersome symptoms. For some people, a low blood pressure is normal, and in general, the lower the blood pressure, the better.
What Does Low Blood Pressure Mean?
Causes of low blood pressure may include:
- Prolonged bed rest
- Decreases in blood volume, such as from major trauma, dehydration, or severe internal bleeding or anemia
- Certain medications, including diuretics, other drugs that treat high blood pressure (hypertension), heart medications such as beta blockers, drugs for Parkinson's disease, tricyclic antidepressants, erectile dysfunction drugs (especially in combination with nitroglycerine), narcotics, and alcohol
- Heart problems, such as abnormally low heart rate, heart valve problems, heart attack, and heart failure
- Pregnancy, especially during the first 24 weeks when it’s common for blood pressure to drop
- Endocrine problems, such as underactive thyroid (hypothyroidism), parathyroid disease, adrenal insufficiency (Addison’s disease), low blood sugar and diabetes
- Problems with the autonomic nervous system, such as Parkinson’s disease
- Neurally mediated hypotension, a disorder that causes blood pressure to drop after standing for long periods
- Nutritional deficiencies, including a lack of vitamins B-12 and folic acid
- Older age
- Severe infection (septic shock)
- Severe allergic reaction (anaphylaxis)
What Are Symptoms of Low Blood Pressure?
Chronically low blood pressure is usually only considered a medical concern if it causes noticeable symptoms such as:
- Lightheadedness
- Fainting
- Dizziness
- Nausea
- Dehydration
- Unusual thirst
- Blurred vision
- Inability to concentrate
- Cold, clammy, pale skin
- Fatigue
- Depression
Extremely low blood pressure can prevent the body’s vital organs from getting the oxygen and nutrients they need which can lead to shock, a medical emergency. Call 911 and get to a hospital’s emergency department (do not drive yourself) if signs of shock are present, such as:
- Cold and sweaty skin
- Rapid, shallow breathing
- Blue skin tone
- Weak and rapid pulse
How Is Low Blood Pressure Diagnosed?
Blood pressure is measured by medical professionals with a sphygmomanometer, a device that includes a cuff placed around the arm and inflated with air until blood cannot flow through the brachial artery. The air is then slowly released until blood starts to flow through the arm again, creating a pounding sound that can be heard by placing a stethoscope close to the elbow.
Blood pressure is expressed in two numbers:
| Systolic blood pressure (the first/top number) | measures the pressure in the blood vessels when the heart beats |
| Diastolic blood pressure (the second/bottom number) | measures the pressure in the blood vessels when the heart is at rest between beats |
When blood pressure is measured, it typically is defined as low, normal, elevated, and high blood pressure. Blood pressure ranges are outlined in the chart below.
| Blood Pressure Category | Blood Pressure Range |
|---|---|
| Low blood pressure | 90/60 mm Hg |
| Normal blood pressure | 120/80 mmHg |
| Elevated blood pressure (prehypertension) | between 120/80 and 139/89 |
| High blood pressure (hypertension) | 140/90 mmHg or more |
What Is the Treatment for Low Blood Pressure?
Low blood pressure may not need treatment if it causes no symptoms. When symptoms occur, treatment depends on the specific symptoms, and may include:
- Drinking more fluids
- Medicines to raise blood pressure
- Adjusting medications that cause low blood pressure
- Never change the dose or regimen of a prescribed medication without first talking to your doctor
- Lifestyle changes
- Changing what and how you eat
- Changing how you sit and stand up
- Compression stockings
From 
Heart Health Resources
https://www.nhlbi.nih.gov/health-topics/low-blood-pressure