Low blood pressure, defined as a reading below 90/60 mmHg, can result from dozens of different causes ranging from harmless to life-threatening. For many people, naturally low blood pressure is simply how their body works and produces no symptoms at all. But when blood pressure drops suddenly or causes dizziness, fatigue, or fainting, something specific is usually driving it.
Heart Problems That Reduce Blood Flow
Your blood pressure depends on your heart pumping with enough force and frequency to keep blood moving through your vessels. When the heart can’t do its job properly, pressure drops. The most common cardiac causes include an abnormally slow heart rate (below 60 beats per minute in some cases), heart valve problems that prevent efficient blood flow, heart failure, and heart attack. Each of these reduces the volume of blood your heart pushes out with every beat, which directly lowers the pressure in your arteries.
Dehydration and Blood Volume Loss
Your blood pressure is partly determined by how much fluid is circulating in your bloodstream. When that volume drops, so does the pressure. Dehydration from not drinking enough water, prolonged vomiting, diarrhea, or heavy sweating is one of the most common and easily fixable causes of low blood pressure. Blood loss from an injury, surgery, or internal bleeding has the same effect but is far more dangerous.
Even mild dehydration can produce noticeable symptoms like lightheadedness when you stand up quickly. Severe volume loss is a medical emergency that can send blood pressure plummeting to levels that starve organs of oxygen.
Medications That Lower Blood Pressure
Drugs designed to treat high blood pressure are, unsurprisingly, a frequent cause of blood pressure that drops too low. Diuretics (which reduce fluid volume), beta blockers (which slow the heart), alpha blockers (which relax blood vessels), calcium channel blockers, and ACE inhibitors can all overshoot their target, especially when doses change or medications are combined.
But plenty of medications that aren’t prescribed for blood pressure can lower it as a side effect. Tricyclic antidepressants, certain antipsychotics, muscle relaxants, drugs used for Parkinson’s disease, and medications for erectile dysfunction all carry this risk. Some are easy to overlook. Tamsulosin, commonly prescribed for prostate problems, is actually an alpha blocker that relaxes blood vessels. Trazodone, often used as a sleep aid, has potent blood-vessel-relaxing properties. If you’ve recently started a new medication and notice dizziness or lightheadedness, the drug itself may be the cause.
Blood Pressure Drops When Standing Up
Orthostatic hypotension is the specific term for blood pressure that drops when you go from sitting or lying down to standing. Gravity pulls blood into your legs and abdomen, temporarily reducing the amount flowing back to your heart. Normally, sensors near your heart and neck arteries detect this shift within seconds and signal your heart to beat faster while tightening your blood vessels to compensate. Orthostatic hypotension happens when that compensation system doesn’t work properly.
Occasional episodes are common and usually triggered by something straightforward: dehydration, low blood sugar, overheating, or getting up after sitting for a long time. Prolonged bed rest, such as during a hospital stay, can also decondition the reflex. More persistent orthostatic hypotension often points to nervous system disorders that damage the body’s automatic blood pressure regulation. Parkinson’s disease, Lewy body dementia, and a condition called pure autonomic failure can all disrupt the signaling pathway between those pressure sensors and your brain.
Blood Pressure Drops After Eating
After a meal, your body diverts extra blood to your digestive system. To compensate, your heart rate increases and blood vessels elsewhere in the body tighten to keep overall pressure stable. In some people, that compensation falls short, and blood pressure drops noticeably within 30 to 60 minutes of eating. This is called postprandial hypotension, and it’s remarkably common in older adults. Studies show roughly 40% of people between ages 65 and 86 experience it. Large, carbohydrate-heavy meals tend to produce the biggest drops.
Hormonal and Endocrine Causes
Several hormone-producing glands play a role in blood pressure regulation, and when they malfunction, low blood pressure can follow. Adrenal insufficiency (sometimes called Addison’s disease) is one of the clearest examples. The adrenal glands sit on top of your kidneys and produce hormones that help your body manage salt, water balance, and stress responses. When they don’t produce enough, blood pressure drops, often worsening when you stand up and causing dizziness or fainting.
Thyroid disorders can also contribute. An underactive thyroid slows many body processes, including heart rate, which can lower blood pressure. Low blood sugar, whether from skipping meals or as a complication of diabetes treatment, triggers a similar drop because the body’s stress-response systems become less effective at maintaining vascular tone.
Severe Infections and Allergic Reactions
Some of the most dangerous causes of low blood pressure involve a sudden, body-wide crisis. In sepsis, a severe infection triggers widespread inflammation that causes blood vessels throughout the body to relax dramatically. This is called distributive shock. The blood vessels become so dilated that pressure plummets, and the small capillaries begin leaking fluid out of the circulation. Organs like the brain, heart, and kidneys can’t get enough blood to function.
Anaphylaxis, a severe allergic reaction, works through a similar mechanism. The immune system releases a flood of chemicals that dilate blood vessels and can cause blood pressure to crash within minutes. Both conditions are medical emergencies where the drop in blood pressure itself becomes the primary threat to survival.
Nutritional Deficiencies
Your body needs certain vitamins to produce healthy red blood cells. Vitamin B12 and folate are both essential for red blood cell production, and when either is deficient, the result is a type of anemia where the body makes fewer, abnormally large red blood cells that don’t carry oxygen efficiently. With fewer functional red blood cells in circulation, blood volume effectively decreases and blood pressure can fall. B12 deficiency is especially common in older adults, people with digestive conditions that impair absorption, and those following strict vegan diets without supplementation.
When Low Blood Pressure Is Normal
Not all low blood pressure is a problem. Some people naturally run below 90/60 mmHg their entire lives without any symptoms. Physically active individuals and endurance athletes often have lower resting blood pressure because their hearts pump more efficiently, moving more blood per beat. In these cases, low blood pressure is a sign of cardiovascular fitness rather than a medical issue. The key distinction is symptoms: low blood pressure only needs attention when it causes dizziness, fainting, blurred vision, nausea, fatigue, or difficulty concentrating.