Why Is My Blood Pressure Low?

Low blood pressure (hypotension) is usually not a problem as long as a person has no troublesome symptoms. Causes of low blood pressure include prolonged bed rest, pregnancy, decreases in blood volume from major trauma, heart problems, certain medications, endocrine problems, severe infection (septic shock), severe allergic reaction (anaphylaxis), and others.

Low blood pressure (hypotension) is a condition in which the force of blood pumping through the arteries is lower than normal.

However, there is no specific measurement at which blood pressure is considered too low, and it is generally not a reason for concern as long as a person has no troublesome symptoms.

For some people, a low blood pressure is normal, and for the most part, the lower the blood pressure reading, the better. 

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

Low, normal, elevated, and high blood pressure is usually defined in the following ranges: 

• Low blood pressure is 90/60 mm Hg
• Normal blood pressure is less than 120/80 mmHg
• Elevated blood pressure levels between 120/80 and 139/89 are considered prehypertension and mean a person is at higher risk for developing high blood pressure
• High blood pressure (hypertension) is 140/90 mmHg or more

Reasons a person’s blood pressure might be low include: 

• Prolonged bed rest
• Pregnancy, especially during the first 24 weeks when it’s common for blood pressure to drop
• 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
• 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 
• Severe infection (septic shock)
• Severe allergic reaction (anaphylaxis)
• 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