Low blood pressure

Also known as hypotension, low blood pressure can happen for a number of  reasons. Symptoms can include:

• Dizziness
• Light headedness
• Fainting
• Feeling weak, shaky or unsteady
• Blurry vision
• Nausea.

If you have naturally low blood pressure that is 90/60 mmHg or lower, you may have no symptoms or need for treatment. Read on for some of the key medical causes of low blood pressure.

Shock

A severe injury that results in clinical shock can trigger low blood pressure, especially when blood loss is involved. You may experience shock after injuries such as burns or other body traumas.

Anaphylactic shock

A rapid and dangerous drop in blood pressure usually accompanies a severe allergic reaction, known as anaphylactic shock. It can be caused by allergies to:

• Food
• Latex
• Insect bites or venom
• Some medicines.

As well as dramatically lowered blood pressure, symptoms may include rapid heart rate, intense itching, rash, and a swollen throat, lips or tongue.

Septic shock

Septic shock is caused by severe bacterial infections that cause significant drops in blood pressure. It happens as fluid leaks from the blood into surrounding tissues. Other symptoms include:

• Headache and muscle aches
• Feeling generally unwell
• Disorientation
• High temperature
• Nausea, vomiting, diarrhoea.

Drug overdose or narcotic abuse

Symptoms of a drug overdose often include a severe drop in blood pressure. Overdosing on opiates such as heroin or codeine can also trigger slow, shallow breathing. This reduces the oxygen getting into your system and can ultimately lead to coma, pulmonary oedema and even death.

Dehydration

Low blood pressure can happen when your body loses more water than it takes in. It results in low blood volume which reduces the oxygen reaching your body tissues. Causes of dehydration include:

• High temperature
• Excess sweating in hot weather
• Strenuous exercise
• Taking diuretics ('water tablets’)
• Vomiting and/or diarrhoea.

A serious complication of dehydration is hypovolaemic shock, which results from low blood volume causing a dramatic drop in blood pressure, and which can be life threatening.

Heart problems

Some heart problems can make it hard for your heart to pump blood around your body. This can trigger low blood pressure and a rapid heart rate. Conditions include:

• Heart rhythm disorders such as atrial flutter
• Heart valve problems 
• Congenital heart problems
• Aortic stenosis (narrowing of aortic heart valve)
• Heart attack
• Heart failure.

Medication reaction or side-effect

Some drugs can trigger low blood pressure. They include:

• Beta-blockers
• Diuretics (‘water tablets’)
• ACE (angiotensin-converting enzyme) inhibitors
• Angiotensin receptor blockers (ARBs)
• Some alpha-blockers
• Some antidepressants.

Hypoglycaemia (low blood sugar)

Hypoglycaemia, which can trigger low blood pressure, occurs in people with diabetes. It can happen after missing a meal, or exercising more than usual. It rarely affects people without diabetes, but can happen after a big meal that’s rich in carbohydrates. This is called reactive hypoglycaemia. It can also happen after fasting or binge drinking, or if you have malnutrition, or a serious liver, kidney or thyroid gland condition.

Thyroid and pituitary gland problems

If you have certain thyroid gland disorders, it is possible to experience low blood pressure and heart rate abnormalities. Another gland, the pituitary, may be underactive, called hypopituitarism. A possible symptom is low blood pressure which can trigger dizziness, weakness and blackouts. Low blood sugar, weight loss, loss of appetite and nausea are also possible symptoms.

Tick bites

Low blood pressure can be a complication of babesiosis, a disease caused by a tick bite. The babesiosis parasite targets red blood cells. In very severe cases symptoms include extremely low blood pressure as well as a high temperature, severe anaemia, and, ultimately, kidney or liver failure.

Anaemia

Anaemia happens when your body doesn’t produce enough red blood cells, so your tissues and organs don’t get enough oxygen. This can result in low blood pressure and an abnormal heart rate. It can be triggered by a lack of nutrients in your diet, such as iron. Iron deficiency anaemia can cause an abnormally rapid heart rate, known as tachycardia. 

Seek medical advice

If your blood pressure is 90/60 mmHg or lower, you probably won’t have any problems. Seek medical help if you experience possible symptoms of low blood pressure like:

• Dizziness
• Blurred vision
• Nausea
• Confusion
• Fainting.

While the symptoms may seem mild, they can put you at risk of a fall or further injury, so don’t hesitate to get help.  

Related reading

• Low blood pressure explained
• A visual guide to heart disease
• Get to the heart of atrial fibrillation
• Diastolic and systolic blood pressure
• DASH diet for heart health
• Quiz: Fun facts about your heart