Low blood pressure, or hypotension, means the force of blood pushing against your artery walls is lower than what’s considered normal. A reading below 90/60 mmHg is the general threshold. For many people, naturally low blood pressure causes no symptoms and is actually a sign of good cardiovascular health. It only becomes a concern when it drops low enough to reduce blood flow to your brain and organs, triggering symptoms like dizziness, fainting, or fatigue.
What the Numbers Mean
Blood pressure is measured in two numbers. The top number (systolic) reflects pressure when your heart beats, and the bottom number (diastolic) reflects pressure between beats. A reading of 120/80 mmHg is considered normal for most adults. When either number falls below 90/60, it’s classified as low.
What matters more than the number itself is the change. A sudden drop of just 20 mmHg, say from 110 to 90 systolic, can make you feel dizzy or faint even if the final number isn’t dramatically low. Someone who normally runs 100/65 with no symptoms has no problem. Someone who suddenly drops from their usual 130/85 to 100/60 might feel terrible. Context matters as much as the reading.
Common Symptoms
Mild low blood pressure often shows up as:
- Dizziness or lightheadedness
- Blurred or fading vision
- Fatigue
- Trouble concentrating
- Nausea
- Fainting
These happen because your brain isn’t getting quite enough blood flow. They tend to come on when you stand up quickly, after eating a large meal, or during prolonged standing. Many people experience them occasionally without having a serious underlying condition.
Severely low blood pressure is a different situation. When pressure drops far enough to starve organs of oxygen, you can go into shock. Signs include confusion (especially in older adults), cold and clammy skin, pale appearance, rapid shallow breathing, and a weak, fast pulse. This is a medical emergency, most often triggered by significant blood loss, severe infection, or a serious allergic reaction.
Types of Low Blood Pressure
Orthostatic Hypotension
This is the most common type and happens when your blood pressure drops after standing up. It’s formally defined as a systolic drop of at least 20 mmHg or a diastolic drop of at least 10 mmHg within three minutes of standing. For people who already have high blood pressure (baseline above 160 mmHg systolic), a drop of 30 mmHg is used as the threshold instead, since the fall tends to be larger. You feel it as a head rush, momentary dimming of vision, or unsteadiness. It’s especially common in older adults and people who are dehydrated.
Postprandial Hypotension
Blood pressure can dip after eating because your body redirects blood flow to the digestive system. This mostly affects older adults and people with conditions that affect the nerves controlling blood vessel tone. Eating smaller, more frequent meals and limiting refined carbohydrates can reduce the effect.
Neurally Mediated Hypotension
This type involves a miscommunication between your heart and brain. When you stand for a long time or encounter certain emotional triggers, your nervous system reflexively dilates blood vessels and slows the heart rate at the wrong moment, causing a sudden drop in pressure. The result is typically dizziness or fainting. It’s the mechanism behind classic vasovagal syncope, the kind of faint people experience from the sight of blood, extreme heat, or standing in one position too long.
What Causes Low Blood Pressure
Some people simply run low and always have. Athletes and people who exercise regularly often have resting blood pressure well below 120/80, and this is healthy. But when low blood pressure is new or worsening, several categories of causes are worth considering.
Dehydration is one of the most common and fixable causes. When you lose more fluid than you take in, whether from heat, exercise, vomiting, or diarrhea, your blood volume drops and pressure falls with it. Even mild dehydration that wouldn’t concern you otherwise can lower blood pressure enough to cause symptoms in susceptible people.
Medications are another frequent culprit. Blood pressure drugs (including water pills and alpha blockers), certain antidepressants, and medications for prostate conditions can all lower blood pressure as a primary or side effect. Alpha blockers, for example, are well known for causing a sudden drop in pressure when you first start taking them, which is why they’re often recommended to be taken at bedtime. If your symptoms started around the time you began a new medication, that connection is worth exploring with your provider.
Heart conditions such as an extremely slow heart rate, heart valve problems, or heart failure can reduce the heart’s ability to pump enough blood to maintain adequate pressure. These tend to cause persistent symptoms rather than occasional episodes.
Hormonal and endocrine issues can also play a role. The adrenal glands produce hormones that help regulate blood pressure, and conditions affecting them (like Addison’s disease) can cause chronically low readings. Thyroid disorders and low blood sugar can contribute as well.
Blood loss, whether from injury, surgery, or internal bleeding (such as a slowly bleeding stomach ulcer), reduces blood volume directly. Significant blood loss leads to hypovolemic shock, the most dangerous form of low blood pressure, marked by a rapid weak pulse, low body temperature, and confusion.
Severe infection and allergic reactions can trigger sudden, life-threatening drops in blood pressure. In sepsis, the body’s response to infection causes blood vessels to dilate widely, and in anaphylaxis, an overwhelming immune reaction does the same. Both require immediate emergency care.
How It’s Diagnosed
Diagnosis starts with simply measuring your blood pressure in different positions: lying down, sitting, and standing. If your readings drop significantly when you shift from lying to standing, that points toward orthostatic hypotension. Your provider will also review your medications, hydration status, and medical history.
If the cause isn’t obvious, a tilt table test can help. You lie flat on a padded table, strapped in securely, and the table is quickly tilted upright to simulate standing. Monitors track your blood pressure, heart rate, and heart rhythm the entire time. This test forces your autonomic nervous system, the network that controls involuntary processes like blood vessel tone, to respond in real time. It’s particularly useful for diagnosing orthostatic hypotension and related conditions where fainting is a recurring problem.
Blood tests may be ordered to check for anemia, blood sugar levels, thyroid function, and adrenal hormone levels if an underlying condition is suspected.
Managing Low Blood Pressure Day to Day
If your low blood pressure isn’t causing symptoms, it generally doesn’t need treatment. But if you’re dealing with frequent dizziness, lightheadedness, or fainting, several practical strategies can make a real difference.
Increasing your fluid intake is the simplest starting point. Staying well hydrated boosts blood volume and can raise pressure noticeably. Adding a bit more salt to your diet works through the same mechanism, since sodium helps your body retain water. This is one of the few situations where extra salt is encouraged rather than restricted, though it depends on your overall health picture.
Standing up slowly gives your cardiovascular system time to adjust. If you’ve been lying down, sit on the edge of the bed for a moment before getting to your feet. Compression stockings can help by preventing blood from pooling in your legs, which is a major contributor to orthostatic drops. Eating smaller, more frequent meals reduces the postprandial dip. Avoiding alcohol helps too, since it dilates blood vessels and promotes fluid loss.
When medications are the cause, adjusting the dose or timing often resolves the problem. If a heart condition, hormonal disorder, or other underlying issue is driving the low readings, treating that condition is the priority. In most cases, once the root cause is addressed, blood pressure stabilizes.