Low blood pressure usually comes down to one of a few things: not enough fluid in your body, a medication side effect, a hormonal shift, or your nervous system not adjusting fast enough when you change positions. A reading below about 90/60 mmHg is generally considered low, but what matters more than the number itself is whether you’re experiencing symptoms like dizziness, lightheadedness, or fatigue. Some people naturally run low without any problems at all.
Dehydration Is the Most Common Culprit
When your body doesn’t have enough water, your total blood volume drops, and so does the pressure pushing blood through your vessels. This is probably the single most frequent reason for unexpectedly low readings. Fever, vomiting, severe diarrhea, intense exercise, and simply not drinking enough fluids can all get you there. Diuretic medications (water pills) can tip the balance too, especially in hot weather or if you’ve been sick.
The fix is often straightforward: drink more fluids, particularly water and beverages with electrolytes. But if dehydration is severe or ongoing, the drop in blood pressure can become dangerous, so persistent symptoms like confusion, rapid breathing, or very dark urine deserve prompt attention.
Medications That Lower Blood Pressure
A surprising number of medications can push your blood pressure down, and not just the ones designed to do so. Blood pressure drugs like diuretics, beta blockers, and alpha blockers are obvious offenders. But several other medications commonly cause low readings as a side effect:
- Certain antidepressants, particularly older tricyclic types and trazodone, which blocks receptors that help maintain blood vessel tone
- Medications for Parkinson’s disease, which affect the same nervous system pathways that regulate blood pressure
- Prostate medications like tamsulosin, which relax smooth muscle and can relax blood vessels too
- Muscle relaxants like tizanidine, which reduce the nervous system signals that keep blood vessels tight
- Erectile dysfunction drugs, which widen blood vessels and can cause a significant pressure drop
If your blood pressure started running low around the time you began a new medication, or after a dose increase, that connection is worth investigating. Don’t stop any prescription on your own, but bring it up at your next visit.
Drops When You Stand Up
If your blood pressure mainly drops when you go from sitting or lying down to standing, that’s called orthostatic hypotension. Normally, when you stand, your body detects the shift in blood flow within seconds. Pressure sensors in your neck and chest signal your nervous system to tighten blood vessels and speed up your heart rate so blood keeps reaching your brain. When that reflex doesn’t work properly, blood pools in your legs and your blood pressure falls.
This happens for two broad reasons. The first is simply low blood volume, from dehydration, blood loss, vomiting, diarrhea, or not eating or drinking enough. The second is nervous system dysfunction, where the reflexes that compensate for standing are impaired. Conditions like Parkinson’s disease, diabetes, and other disorders that affect the autonomic nervous system (the part that controls involuntary functions like heart rate and digestion) make this type of blood pressure drop more likely.
You might notice it most in the morning, after a hot shower, or after standing still for a long time. The classic symptom is a head rush or brief lightheadedness that passes within a few seconds, but in more severe cases it can cause blurred vision, weakness, or fainting.
Drops After Eating
Blood pressure can also fall after meals, a pattern called postprandial hypotension. After you eat, your body redirects blood flow to your digestive tract. Normally, your heart rate speeds up and blood vessels elsewhere tighten to compensate. When that compensation falls short, pressure drops.
This is most common in adults over 65, and the risk is higher if you have high blood pressure, diabetes, heart failure, Parkinson’s disease, or kidney disease. Eating smaller, more frequent meals and limiting high-carbohydrate foods can help reduce the drop. Staying hydrated before and during meals also makes a difference.
Pregnancy
Blood pressure commonly drops during pregnancy, especially in the first and second trimesters. Your circulatory system expands rapidly to supply the growing fetus, and blood volume hasn’t fully caught up yet. This can cause dizziness and lightheadedness, particularly when standing quickly. In most cases, blood pressure gradually returns to pre-pregnancy levels in the third trimester or after delivery.
Hormonal and Endocrine Conditions
Your hormones play a direct role in blood pressure regulation, and disruptions to certain glands can cause persistent low readings. Addison’s disease is one of the clearest examples. The adrenal glands, which sit on top of your kidneys, produce cortisol and a hormone called aldosterone that helps balance sodium and potassium levels to keep blood pressure stable. In Addison’s disease, the adrenals don’t produce enough of either hormone, leading to chronically low blood pressure, particularly when standing. People with Addison’s disease often experience dizziness or near-fainting when they get up from a chair or bed.
Low blood sugar can also lower blood pressure, and diabetes itself is a risk factor. Thyroid problems, particularly an underactive thyroid, sometimes contribute as well. If your blood pressure has been gradually trending downward alongside other symptoms like unusual fatigue, weight changes, or salt cravings, an endocrine issue is worth considering.
Heart Problems
Your heart is the pump that generates blood pressure, so conditions that weaken it or reduce its output can bring your numbers down. Heart valve problems, heart failure, and very slow heart rates all reduce the amount of blood pushed out with each beat. These tend to cause low blood pressure alongside other symptoms like shortness of breath, chest tightness, or swelling in the legs, rather than low blood pressure in isolation.
Serious Infections and Allergic Reactions
Severe infections that spread to the bloodstream can cause a dangerous drop in blood pressure as part of the body’s overwhelming inflammatory response. Severe allergic reactions (anaphylaxis) can do the same, rapidly widening blood vessels and causing blood pressure to plummet. These are medical emergencies and typically come with dramatic, sudden symptoms rather than the mild, chronic low readings most people are searching about.
What the Symptoms Feel Like
Low blood pressure doesn’t always cause noticeable symptoms. When it does, the most common ones are lightheadedness, dizziness, and a foggy or unfocused feeling. You might notice blurred vision, nausea, fatigue, or a general sense of weakness. Some people feel cold or clammy. In more extreme cases, fainting is possible.
The symptoms tend to be worst when blood pressure drops quickly, like when you stand up or after a large meal. A person whose blood pressure is naturally on the low side but stable may feel perfectly fine, while someone whose pressure drops suddenly from 130 to 90 might feel terrible even though 90 isn’t dramatically low on paper.
How Low Blood Pressure Is Evaluated
If low blood pressure is causing symptoms, your provider will likely start with repeat readings in different positions: lying down, sitting, and standing. A significant drop when moving from lying to standing points toward orthostatic hypotension. Blood work can check for dehydration, anemia, blood sugar levels, and hormonal imbalances.
For cases where the cause isn’t obvious, a tilt table test can help. You lie on a padded table with blood pressure cuffs on your arm and finger and heart monitors attached. The table is then tilted to about a 70-degree angle within 10 seconds, simulating standing. You stay upright for up to 45 minutes while your blood pressure, heart rate, and rhythm are continuously recorded. A large drop in blood pressure during the test, especially if accompanied by dizziness or fainting, confirms a diagnosis of orthostatic hypotension or a related condition. A normal result means your body handled the position change without significant issues.
When Low Blood Pressure Becomes Dangerous
Most cases of mildly low blood pressure are more of a nuisance than a danger. The situation becomes serious when pressure drops so far that organs aren’t getting enough blood. Losing more than 15 to 20 percent of your blood volume, whether from injury, internal bleeding, or severe dehydration, can cause hypovolemic shock. The signs include cool and clammy skin, rapid weak pulse, confusion, anxiety, pale skin, rapid breathing, reduced or absent urine output, and eventually loss of consciousness. This is a medical emergency that requires immediate treatment.
Outside of shock, chronically low blood pressure with frequent lightheadedness or fainting episodes raises your risk of falls and injuries, which is especially concerning for older adults. If you’re having repeated near-fainting spells or have actually fainted, that warrants a thorough workup rather than a wait-and-see approach.