Low blood pressure, or hypotension, means your blood isn’t pushing against your artery walls with enough force to reliably deliver oxygen to your brain and organs. A reading below 90/60 mmHg is generally considered low, but the number alone doesn’t tell the whole story. Some people walk around with naturally low readings and feel perfectly fine. The real concern starts when low blood pressure causes symptoms or drops suddenly. A change of just 20 mmHg in systolic pressure (the top number) can be enough to make you dizzy or faint.
Why Low Blood Pressure Causes Symptoms
Your brain sits at the top of your body and depends on steady blood flow to function. When pressure drops, less oxygen-rich blood reaches your brain, and that’s when you start to notice problems. The most common symptoms include dizziness or lightheadedness, blurred or fading vision, fatigue, trouble concentrating, nausea, and fainting. These tend to come on when you stand up quickly, haven’t eaten, or are dehydrated.
Severely low blood pressure can starve both the brain and heart of oxygen, potentially causing lasting damage. When pressure drops far enough to compromise organ function, it becomes a medical emergency called shock. The signs of shock look different from everyday lightheadedness: cold, clammy skin, rapid shallow breathing, a weak and fast pulse, confusion (particularly in older adults), and noticeable paleness.
When Low Blood Pressure Is Normal
Not everyone with a low reading has a problem. Many young, healthy, physically active people have resting blood pressure well below 90/60 and never experience symptoms. Athletes, in particular, often have low resting pressure because their hearts pump more efficiently. If your readings have always been on the low side and you feel fine, there’s typically nothing to worry about. Low blood pressure only becomes clinically meaningful when it’s causing symptoms or represents a sudden change from your usual numbers.
Common Causes
Dehydration is one of the most frequent and fixable causes. When your blood volume drops because you haven’t taken in enough fluid, or you’ve lost fluid through sweating, vomiting, or diarrhea, there simply isn’t enough blood to maintain adequate pressure. This is why low blood pressure often shows up during hot weather, after exercise, or during illness.
Pregnancy commonly lowers blood pressure as well. Blood vessels expand and the circulatory system undergoes significant hormonal changes to support a growing baby. This naturally pulls pressure down from pre-pregnancy levels, especially in the first and second trimesters. People who are underweight or have low muscle mass tend to be more susceptible to low blood pressure during pregnancy.
Heart conditions, hormonal disorders (like thyroid problems or adrenal insufficiency), blood loss, severe infection, and severe allergic reactions can all cause blood pressure to fall. Nutritional deficiencies, particularly in iron, vitamin B12, and folate, can reduce red blood cell production and lower pressure over time.
Medications That Lower Blood Pressure
A wide range of medications can push blood pressure down, sometimes more than intended. Diuretics (water pills), both the milder thiazide type and stronger loop diuretics, reduce fluid volume and commonly cause drops in pressure. Beta blockers can slow the heart rate enough to lower pressure. Calcium channel blockers and other blood pressure medications can overshoot their target, especially in older adults or when doses change.
Less obviously, many medications that act on the brain also lower blood pressure as a side effect. Older antidepressants (tricyclics) and drugs used for psychosis or agitation block receptors in blood vessels that help maintain pressure. Medications for Parkinson’s disease frequently cause blood pressure drops. Even some drugs for erectile dysfunction and weight loss can lower readings. If you notice new symptoms after starting or adjusting a medication, that connection is worth exploring with your prescriber.
Types of Low Blood Pressure
The type that affects the most people is orthostatic hypotension, sometimes called postural hypotension. It happens when you stand up and your body fails to compensate for the 500 to 1,000 milliliters of blood that naturally pools in your legs and abdomen due to gravity. Normally, sensors in your blood vessels detect the shift and signal your nervous system to tighten blood vessels and speed up your heart rate. When that reflex doesn’t work well enough, pressure drops. The clinical threshold is a fall of 20 mmHg systolic or 10 mmHg diastolic within three minutes of standing.
In some people, orthostatic hypotension is neurogenic, meaning the autonomic nervous system itself is damaged and can’t generate the normal compensating response. This is more common in people with Parkinson’s disease, diabetes, or other conditions that affect nerve function. Postprandial hypotension, a drop in blood pressure after eating, is closely related. After a meal, blood is redirected to the digestive system, and in people whose nervous system is already compromised, this redistribution can pull pressure down significantly.
Neurally mediated hypotension occurs when the brain and heart miscommunicate during prolonged standing. Instead of signaling blood vessels to tighten, the brain tells the heart to slow down and vessels to relax, causing pressure to plummet. This is the mechanism behind many fainting episodes in otherwise healthy people, particularly younger adults.
Managing Low Blood Pressure
The first and most effective step is increasing fluid intake. Baseline recommendations are roughly 125 ounces (3.7 liters) per day for men and 91 ounces (2.7 liters) for women, though people with low blood pressure often benefit from drinking more than the minimum, particularly before long periods of standing or activities that tend to trigger symptoms.
Adding salt to your diet can raise blood pressure, but this needs to be done carefully and in conversation with a healthcare provider, since too much sodium creates its own set of problems. For people with orthostatic hypotension specifically, waist-high compression stockings can make a meaningful difference. They gently squeeze blood vessels in the legs, raising blood pressure by about 5 to 10 mmHg. The key is wearing them during the day and removing them at night.
Simple behavioral changes also help. Standing up slowly, especially first thing in the morning. Eating smaller, more frequent meals to reduce postprandial drops. Avoiding alcohol, which dilates blood vessels. Crossing your legs or tensing your thigh muscles when you feel a wave of dizziness coming on. These aren’t dramatic interventions, but for people with chronic low blood pressure, stacking several of them together can significantly reduce how often symptoms interfere with daily life.
If a medication is the likely cause, adjusting the dose or switching to a different drug often resolves the problem. This is one of the most common and most correctable causes of low blood pressure, particularly in older adults taking multiple medications.
Signs That Need Immediate Attention
Occasional lightheadedness when you stand up too fast is common and usually harmless. But certain patterns signal something more serious: fainting repeatedly, feeling confused, noticing your skin turning pale and clammy, or having a pulse that feels rapid and weak. These are signs that blood pressure has dropped low enough to compromise organ function. A sudden, sharp drop in someone who normally has stable readings, especially after an injury, infection, or allergic reaction, can progress to shock quickly and requires emergency care.