Blood pressure below 90/60 mmHg is considered low. That means the top number (systolic) is under 90, or the bottom number (diastolic) is under 60, or both. But here’s the important nuance: most healthcare professionals only consider low blood pressure a problem when it causes symptoms. Some people walk around at 85/55 their entire lives and feel perfectly fine.
What the Numbers Mean
Blood pressure is measured in two numbers. The top number (systolic) reflects the pressure in your arteries when your heart beats. The bottom number (diastolic) measures the pressure between beats, when your heart is resting. A normal reading is below 120/80 mmHg. Once either number drops below the 90/60 threshold, it’s classified as hypotension.
Unlike high blood pressure, there’s no formal staging system for low blood pressure. The 2025 American Heart Association guidelines define categories for normal, elevated, and high blood pressure in detail, but don’t set an official lower limit. That’s because the clinical significance depends almost entirely on whether you have symptoms, not on hitting a specific number.
When Low Blood Pressure Actually Matters
A reading of 88/58 in someone who feels energetic and alert is not a medical concern. But the same number in someone who feels dizzy every time they stand up is a different story. Symptoms that signal your blood pressure is too low for your body include:
- Dizziness or lightheadedness
- Blurred or fading vision
- Fainting or nearly fainting
- Fatigue and trouble concentrating
- Nausea
A sudden drop matters more than a consistently low reading. A decrease of just 20 mmHg in the top number can make you dizzy or cause you to faint. So if your systolic pressure falls from 110 to 90 in a short period, that’s more dangerous than someone whose pressure sits at 88 all the time.
Extreme drops can lead to shock, which is a medical emergency. Signs of shock include confusion (especially in older adults), cold and clammy skin, rapid shallow breathing, and a weak, fast pulse. In critical care settings, doctors generally aim to keep a patient’s average arterial pressure at or above 65 mmHg to ensure organs are getting enough blood flow.
Types of Low Blood Pressure
Orthostatic Hypotension
This is the most common type, and it happens when your blood pressure drops after you stand up. The diagnostic threshold is a drop of 20 mmHg or more in systolic pressure, or 10 mmHg or more in diastolic pressure, within two to five minutes of standing. It’s especially common in older adults and can increase fall risk significantly.
Postprandial Hypotension
Some people experience a blood pressure drop after eating. This is defined as a systolic drop of about 20 mmHg following a meal. It’s more common in older adults and people with conditions affecting the nervous system, like Parkinson’s disease.
Neurally Mediated Hypotension
This type occurs when your nervous system overreacts to a trigger, such as standing for a long time, stress, heat, or even the sight of medical instruments. Your blood vessels suddenly dilate and your heart rate slows, sending blood pressure plummeting. It’s a common cause of fainting in younger adults and is sometimes diagnosed using a tilt table test, which monitors your blood pressure and heart rate as you’re moved from lying flat to an upright position.
Common Causes
Dehydration is one of the most straightforward causes. When your body loses more fluid than it takes in, blood volume drops, and pressure follows. Prolonged bed rest, significant blood loss, severe infections, and serious allergic reactions can all drive blood pressure dangerously low.
Medications are a major contributor. Blood pressure drugs can sometimes overshoot their target, but many non-cardiac medications also lower blood pressure as a side effect. Water pills (both thiazide and loop diuretics) cause it through fluid loss. Alpha blockers, often prescribed for prostate issues, commonly cause significant drops. Heart medications like nitroglycerin can trigger sudden pressure drops. Beta blockers can lower both blood pressure and heart rate.
Several classes of psychiatric and neurological medications also carry risk. Older antidepressants (tricyclics) and certain newer ones can cause blood pressure to drop when standing. Medications for Parkinson’s disease, antipsychotics, and some anxiety medications all have similar effects. If you’ve recently started a new medication and notice dizziness when standing, the timing is probably not a coincidence.
Low Blood Pressure During Pregnancy
Blood pressure commonly dips during the first and second trimesters as the circulatory system expands rapidly to support the growing baby. This is a normal physiological change. Normal blood pressure during pregnancy is 120/80 mmHg or lower. Most pregnant people won’t need treatment for lower readings unless symptoms like persistent dizziness or fainting develop. Blood pressure typically returns to pre-pregnancy levels in the third trimester or after delivery.
What You Can Do About It
If your blood pressure runs low but you feel fine, there’s generally nothing to treat. For people who do experience symptoms, simple strategies can make a real difference. Drinking more water increases blood volume. Adding a bit of extra salt to your diet (with your doctor’s input) helps retain fluid. Standing up slowly, especially first thing in the morning, gives your body time to adjust.
Compression stockings can help prevent blood from pooling in your legs when you stand. Eating smaller, more frequent meals may reduce postprandial drops. Avoiding alcohol and staying out of prolonged heat both help, since both dilate blood vessels and lower pressure further.
If medications are the cause, adjusting the dose or switching to a different drug often resolves the problem. For persistent orthostatic hypotension that doesn’t respond to lifestyle changes, there are prescription options that help raise blood pressure, though these are typically reserved for cases that significantly affect daily life or increase fall risk.