Blood pressure is generally considered low when a reading falls below 90/60 mm Hg, but the number on its own does not make it a problem. Low blood pressure matters when it produces symptoms: dizziness, light-headedness, fatigue, blurred vision or fainting. Plenty of healthy people simply run low and feel nothing at all.
What blood pressure reading counts as low?
The NHLBI sets the threshold plainly: "Low blood pressure is blood pressure that is lower than 90/60 mm Hg." The MedlinePlus entry on hypotension frames the normal adult range as sitting "between 90/60 mmHg and 120/80 mmHg", and adds an important caveat: "a drop of as little as 20 mmHg can cause problems for some people". In other words, the change from your own baseline can matter as much as the absolute figure.
| Reading | How it is generally described |
|---|---|
| Below 90/60 mm Hg | Low blood pressure (hypotension), per the NHLBI threshold |
| 90/60 to 120/80 mm Hg | The normal adult range described by MedlinePlus |
| A fall of about 20 mm Hg from your usual reading | Enough to cause symptoms in some people, even when the number still looks normal |
One pattern has its own definition. Orthostatic hypotension is "a sustained drop in systolic blood pressure (SBP) of at least 20 mm Hg or diastolic blood pressure of 10 mm Hg within 3 minutes of standing after being supine for at least 5 minutes". It is common with age, affecting roughly 1 in 5 people living in the community aged 60 or over, and more than a quarter of those aged 85 and over.
What are the symptoms of low blood pressure?
The NHLBI and MedlinePlus between them list the following. Symptoms are what turn a low reading into a condition worth investigating.
- Dizziness, particularly on standing up
- Light-headedness
- Fainting (syncope)
- Blurry vision
- Fatigue and sleepiness
- Weakness
- Confusion
- Nausea or vomiting
- Headache
- Neck or back pain
- Heart palpitations
The MedlinePlus overview of low blood pressure draws the line clearly: "Low blood pressure is a problem only if it causes dizziness, fainting or in extreme cases, shock." Some people carry low readings for life with no symptoms, and for them those readings are simply normal. Persistent tiredness with no obvious explanation is worth a proper look either way, and our piece on when tiredness needs a doctor covers how to judge that.
What causes low blood pressure?
The NHLBI groups the contributing factors as blood loss, dehydration, diabetes, heart arrhythmias, blood pressure or depression medications, pregnancy, and disorders of the autonomic nervous system. MedlinePlus adds a longer list of medicines. Sorted into categories:
| Category | Examples |
|---|---|
| Fluid loss | Dehydration from not drinking enough fluids, vomiting, diarrhoea or heat |
| Blood loss | Bleeding from injury, surgery or an internal source |
| Medicines | Diuretics, heart and blood pressure medicines, certain antidepressants, anti-anxiety medicines, painkillers, and medicines used for surgery |
| Alcohol | Listed by MedlinePlus among the substances that lower blood pressure |
| Pregnancy | Blood pressure commonly runs lower than usual during pregnancy |
| Heart and circulation | Heart rhythm problems and heart failure, where the pump cannot maintain output |
| Hormonal and nerve conditions | Diabetes and autonomic nervous system disorders, which disturb the reflex that holds pressure up when you stand |
Medicines are the category most often missed, because the effect can begin some time after a prescription starts or changes. That is a reason to raise it with the prescriber, never a reason to stop anything yourself. Our explainer on what to know about blood pressure medication sets out how the classes differ, and cold medicine and high blood pressure covers the over-the-counter side of the same question.
How is low blood pressure usually managed day to day?
These are general measures described by MedlinePlus and the NHLBI, not a treatment plan. Which of them fit you, and whether anything more is needed, is a conversation with a clinician who can see the cause.
- Drink more fluids. Dehydration is the most reversible cause on the list.
- Get up slowly after sitting or lying down, rather than standing in one movement.
- Avoid standing still for long stretches, which lets blood pool in the legs.
- Skip alcohol, which MedlinePlus lists among the things that lower blood pressure.
- Ask about compression stockings, which are used to stop blood pooling in the legs.
- Ask about your current medicines. The NHLBI lists adjusting current medications among the approaches used, which is a decision for your prescriber alone.
If symptoms hit, MedlinePlus advises sitting or lying down right away, then raising your feet above heart level.
When is low blood pressure an emergency?
Call emergency services immediately if low blood pressure comes with signs of shock. Shock means organs are not receiving enough blood, and it is a medical emergency rather than something to monitor at home. The NHLBI describes the warning signs as "cold and sweaty skin, rapid breathing, a blue skin tone, or a weak and rapid pulse".
Treat the following combination as urgent:
- Confusion or a sudden change in alertness
- Cold, clammy or sweaty skin, sometimes with a blue or grey tone
- Rapid, shallow breathing
- A weak, rapid pulse
- Fainting, especially with chest pain, breathlessness or after an injury
Fainting for the first time, fainting more than once, or fainting alongside any of the above deserves urgent assessment rather than a wait-and-see approach.
How is low blood pressure different from high blood pressure?
They are opposite problems with opposite time courses. High blood pressure is mostly silent and does its damage slowly, over years, through the strain it puts on vessels, heart, kidneys and eyes, which is why it is screened for and treated even when you feel fine. Low blood pressure is usually the reverse: it announces itself through symptoms in the moment, and if there are no symptoms it often needs no treatment at all.
That difference explains why the two are handled so differently. High readings are managed to prevent future events. Low readings are investigated to explain present ones, and the useful question is less "how do I raise this number" than "what is pulling it down". For the fuller picture of how pressure, flow and circulation fit together, see our heart and circulation guide.
