Low blood pressure, called hypotension, is a reading below 90/60 mmHg. For context, normal blood pressure for most adults sits under 120/80 mmHg. Having low blood pressure isn’t always a problem. Some people run on the low side their entire lives without symptoms. It becomes a concern when it drops enough to cause dizziness, fainting, or other signs that your brain and organs aren’t getting adequate blood flow.
What the Numbers Mean
A blood pressure reading has two numbers. The top number (systolic) measures pressure when your heart pumps. The bottom number (diastolic) measures pressure between beats. Low blood pressure is typically defined as either number falling below 90/60 mmHg. A reading of 85/55, for example, would qualify. But there’s no sharp cutoff where “normal” becomes “low.” What matters more than the number itself is whether you feel symptoms and how far your pressure has dropped from its usual baseline.
Common Symptoms
When blood pressure drops low enough to reduce blood flow to the brain, you’ll feel it. The most common symptoms are dizziness or lightheadedness, especially when standing up quickly. You might also experience blurred or fading vision, fatigue, trouble concentrating, nausea, or fainting.
Many people with chronically low blood pressure have no symptoms at all. If you feel fine and your readings happen to be on the low side, that’s generally not a concern. The symptoms matter more than the number.
Types of Low Blood Pressure
Low blood pressure isn’t one condition. It shows up in several distinct patterns depending on what triggers the drop.
Orthostatic Hypotension
This is the most recognizable type: a sudden drop in blood pressure when you stand up from sitting or lying down. Normally, when you stand, gravity pulls 500 to 800 ml of blood into the veins of your lower body. Your nervous system detects this shift almost instantly and compensates by tightening blood vessels and speeding up your heart rate to push blood back to your brain. In people with orthostatic hypotension, that compensating reflex is too slow or too weak. The result is a head rush, tunnel vision, or in some cases, fainting within seconds of standing.
Postprandial Hypotension
Blood pressure can drop after eating a meal, particularly a large one. Digestion redirects blood flow to the gut, and in some people, the body doesn’t compensate well enough to maintain pressure elsewhere. This type is most common in older adults.
Neurally Mediated Hypotension
Sometimes called vasovagal syncope or reflex fainting, this happens when the nervous system misfires in response to a trigger like prolonged standing, pain, fear, or the sight of blood. Instead of maintaining blood pressure, the brain signals the heart to slow down and blood vessels to widen at the same time. The combined effect causes a rapid drop in pressure that can lead to fainting. This is the classic “passed out at the sight of a needle” scenario, and it’s one of the most common causes of fainting in otherwise healthy people.
What Causes Low Blood Pressure
The list of potential causes is long, which is partly why doctors focus on whether symptoms are present before investigating further.
Dehydration is one of the simplest and most common causes. When you don’t drink enough fluids, or lose fluid through vomiting, diarrhea, or heavy sweating, your blood volume drops and pressure follows. Heart conditions, including heart failure, abnormal heart rhythms, and valve problems, can also reduce the heart’s ability to pump blood effectively.
Endocrine disorders play a role too. Underactive thyroid, adrenal insufficiency (Addison’s disease), and low blood sugar can all lower blood pressure. Nerve damage from diabetes can impair the reflexes that regulate pressure. Severe infections that spread to the bloodstream can cause a dangerous drop in pressure as part of the body’s overwhelming inflammatory response. Significant blood loss from injury or internal bleeding is another cause that requires immediate attention.
Medications That Lower Blood Pressure
Drugs are among the most common culprits, especially in older adults taking multiple prescriptions. The obvious ones are blood pressure medications themselves: diuretics (water pills), beta-blockers, and alpha-blockers. But plenty of non-cardiovascular drugs cause low blood pressure as a side effect too. Tricyclic antidepressants carry a particularly high risk. Antipsychotic medications, certain sleep aids, and anti-anxiety drugs in the benzodiazepine family can all contribute. If your symptoms started or worsened after beginning a new medication, that connection is worth exploring with your prescriber.
Pregnancy
Blood pressure naturally drops in early pregnancy. It typically falls at the very beginning, then gradually rises throughout the pregnancy and returns to pre-pregnancy levels by around 36 weeks. This dip is a normal part of the circulatory changes that support a growing fetus. Mild dizziness or lightheadedness in the first and second trimesters is common and usually not a sign of a problem, though significant or persistent symptoms are worth mentioning to your provider.
How Low Blood Pressure Is Diagnosed
Diagnosis starts with a simple blood pressure reading, often taken in multiple positions: lying down, sitting, and standing. If your pressure drops significantly when you move from lying to standing (typically a drop of 20 mmHg systolic or more within a few minutes), that points to orthostatic hypotension.
For people who faint without an obvious explanation, a tilt table test can help reproduce the episode in a controlled setting. You lie flat on a table with straps holding you in place while monitors track your heart rate, blood pressure, and oxygen levels. The table is then tilted upward to simulate standing. If your pressure drops and symptoms appear, the test confirms the diagnosis and helps identify the type of hypotension involved.
Beyond that, your doctor may check for underlying causes with blood tests looking at thyroid function, blood sugar, or signs of anemia. Heart monitoring or imaging can rule out rhythm problems or structural issues.
Treatment and Daily Management
For many people, low blood pressure responds well to straightforward lifestyle changes without medication. Increasing your fluid intake is the first step. Staying well-hydrated keeps blood volume up and makes drops less likely. Adding more salt to your diet can also help, since sodium holds water in the bloodstream. Most people with high blood pressure are told to limit sodium to under 2,300 mg per day (about a teaspoon of salt). If you have low blood pressure, your doctor may actually encourage you to exceed that amount. The minimum your body needs is only about 500 mg a day, so there’s a wide range to work with depending on your situation.
Compression stockings that squeeze the veins in your legs can prevent blood from pooling when you stand. Simple habits help too: getting up slowly from bed or a chair, avoiding standing in one position for long periods, and eating smaller, more frequent meals if postprandial drops are an issue.
When lifestyle changes aren’t enough, medications are available. The main options work by either increasing blood volume or tightening blood vessels to maintain pressure. One commonly prescribed drug is a synthetic steroid that helps your body retain salt and water, expanding blood volume. Another works by directly constricting blood vessels to raise pressure. These are typically reserved for people with persistent symptoms that interfere with daily life.
When Low Blood Pressure Is Dangerous
Chronically low blood pressure with no symptoms is rarely dangerous. The concern arises when pressure drops suddenly and severely, which can progress to shock. In shock, organs don’t receive enough blood to function. Signs include cold, clammy, pale skin, rapid and shallow breathing, confusion, and a weak but fast pulse. This is a medical emergency that can result from severe bleeding, serious infection, a severe allergic reaction, or major heart problems. Shock requires immediate treatment to restore blood flow to vital organs.
Even outside of emergency scenarios, repeated fainting spells pose a real injury risk from falls. Older adults are especially vulnerable to fractures and head injuries from syncope-related falls, which is one reason doctors take recurrent fainting seriously even when the underlying cause isn’t life-threatening.