What Causes Low Blood Pressure? 8 Possible Reasons

Low blood pressure can be caused by mild or temporary conditions like dehydration, a vitamin deficiency, hormonal changes or pregnancy. It may also be as sign of a more serious illness, like cardiovascular disease or internal bleeding. In 

Blood pressure is considered by low when measured under 90 / 60 mmHg. This may be normal in some people, while others may present with symptoms like dizziness, fainting or fatigue. 

If you have low blood pressure that presents with symptoms, it is important to be assessed by a doctor immediately to identify the underlying cause and to initiate treatment. 

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Main causes

The main causes of low blood pressure include: 

1. Dehydration

Dehydration is the result of excessive fluid loss, leading to less blood volume and reduced blood pressure. It is associated with symptoms like weakness, fainting and fatigue. 

Dehydration is more common in older adults and children (especially in the summer) and in people who take diuretics inappropriate. 

What to do: You should aim to replenish fluids by drink water with electrolytes, to replace minerals that were lost from dehydration. Severe dehydration may require treatment in a hospital setting with IV fluids. 

2. Vitamin B12 or folic acid deficiency

Vitamin B12 or folic acid are vitamins that are important for the formation of red blood cells in the blood. Reduced levels can lead to anemia, which is characterized by a decrease in red blood cells and can lead to low blood pressure. 

Some signs of anemia include weakness, pallor, tingling hands or feet, arm and leg stiffness and decreased sensitivity. Learn more about anemia symptoms and complete our online symptom checker if you suspect you may have this condition. 

What to do: You should see a doctor if you suspect you may have anemia so that the underlying cause can be identified and corrected. A vitamin B12 or folic acid deficiency can be corrected with a B12 diet or folic acid diet, which promote increased consumption of foods that are rich in these minerals. 

Further supplementation may be necessary for low levels. B12, for example, can be replenished with regular B12 injections

3. Medication use

There are many types of medications that can lead to a significant drop in blood pressure if taken for prolonged periods of time. 

Some medications with this side effect include high blood pressure medications, diuretics, heart medication, antidepressants and medication or erectile dysfunction.

What to do: If you are taking any of these medications and notice symptoms of low blood pressure, it is important to see your doctor to assess whether dosing should be reassessed or if the medication should be discontinued. 

4. Hormonal changes

Hormonal changes caused by the thyroid or adrenal glands can stimulate vasodilation, leading to a significant drop in blood pressure. Read more about symptoms of thyroid problems if you suspect your may be experiencing hormone fluctuations.

What to do: It is important to consult an endocrinologist for testing if you suspect a hormonal problem. Results can help to guide the most appropriate treatment approach. 

5. Extensive bleeding

Internal bleeding happens within the body, making it difficult to identify. Large blood losses, however, will typically lead to drops in blood pressure. 

Low blood pressure can also be caused by significant external bleeding. Major blood losses can lead to symptoms like weakness, dizziness ,difficulty breathing and constant headaches. 

What to do: If you suspect you may be experiencing a major bleed, proceed immediately to the hospital for assessment. Once bleeding is stabilized, treatment will be initiated to prevent worsening. 

6. Cardiac problems

Changes to heart functioning can lead to reduced blood pressure, as poor heart functioning can reduce the volume of blood circulating in the body. The most common diseases associated with low blood pressure include cardiac failure, valve problems and arrhythmias. 

In these cases, drops in blood pressure may also cause symptoms like chest pain, excessive fatigue, shortness of breath and cold sweats. Learn more about the symptoms of heart disease and complete our online symptom checker if you suspect you may have a cardiac condition.

What to do: If you have a family history of cardiac disease or if you suspect you may have a heart issue, you should see a cardiologist for assessment and possible treatment. 

7. Severe infection

Although it is rare, low blood pressure may also occur due to a severe infection in the body, also known as sepsis or septic shock. This occurs due to the spread of bacteria throughout the body, leading to toxin build-up in the blood vessels. 

What to do: A systemic infection that appears suddenly with symptoms like weakness, dizziness and fainting should be assessed urgently in the hospital. It is often treated with IV antibiotics and continuous monitoring. 

8. Pregnancy

It is common for pregnant women to present with decreased blood pressure, especially in the first 24 weeks of gestation. Blood pressure will often normalize after delivery. Low blood pressure occurs due to blood vessel expansion from increased fluid circulating in the system, which is necessary for nutrients to reach the fetus. 

What to do: Generally speaking, treatment for mildly low blood pressure is not needed during pregnancy. Women are encouraged to drink plenty of water, to wear light and comfortable clothing, and to aim for 3 primary meals with 2 to 3 snacks per day. Women should also avoid prolonged standing, taking very hot baths and getting up too quickly from sitting or standing. 

Depending on the cause of low blood pressure, the OB may prescribe medication or supplements.  

When to see a doctor

You are advised to see a doctor when blood pressure reduces by more than 40 mmHg, or if it is accompanied by symptoms like: 

  • Dizziness and nausea
  • Fainting
  • Excessive thirst
  • Difficulty concentrating
  • Blurry vision
  • Excessive fatigue
  • Cold and pale skin 

Symptoms can be relieved by lying down with your legs elevated to promote adequate blood flow. Check out other tips for raising blood pressure that you can initiate if you start to feel symptoms. If symptoms persist for more than 10 minutes, you should seek medical attention.