Low blood pressure, clinically called hypotension, is a reading below 90/60 mmHg. It can result from dozens of different causes, ranging from something as routine as pregnancy or standing up too fast to something as urgent as a severe infection or internal bleeding. For many people, low blood pressure produces no symptoms at all and is simply their normal baseline. It becomes a problem when it causes dizziness, fainting, fatigue, or blurred vision, which signals that your brain and organs aren’t getting enough blood flow.
Medications Are the Most Common Culprit
If your blood pressure has recently dropped, the first place to look is your medicine cabinet. Several categories of drugs are strongly linked to blood pressure drops, especially when you stand up. Blood pressure medications themselves are the obvious ones, particularly alpha blockers, beta blockers, and water pills (diuretics). But the list extends well beyond heart drugs. Certain antidepressants, antipsychotic medications, drugs for erectile dysfunction, and nitrate-based medications for chest pain all interfere with your body’s ability to tighten blood vessels when you change position.
The pattern is usually predictable: you stand up from sitting or lying down, and your blood pressure fails to compensate quickly enough. This is called orthostatic hypotension, and it affects an estimated 7% to 10% of adults who take blood pressure medications. It’s especially common in older adults. If you’ve started a new medication or had a dose increase and notice lightheadedness when standing, the timing is probably not a coincidence.
Dehydration and Blood Volume Loss
Your blood pressure depends partly on having enough fluid in your blood vessels. When that volume drops, pressure drops with it. Dehydration from not drinking enough water, heavy sweating, vomiting, or diarrhea can all lower your blood volume enough to cause symptoms. This is also why donating blood can make some people feel faint.
More severe fluid loss pushes this into dangerous territory. Significant bleeding, whether from an injury, surgery, or an internal source like a stomach ulcer, can cause what’s known as hypovolemic shock. In this situation, there simply isn’t enough blood circulating to supply your organs, and blood pressure plummets. This is a medical emergency that requires immediate treatment.
Heart and Circulatory Problems
Your heart is the pump that maintains blood pressure, so anything that weakens its pumping ability can lower your readings. Heart failure, heart valve disorders, and very slow or irregular heart rhythms all reduce the amount of blood your heart pushes out with each beat. When cardiac output drops, blood pressure follows.
These causes tend to produce persistent low blood pressure rather than sudden drops, and they usually come with other symptoms like shortness of breath, swelling in the legs, or chest discomfort. If low blood pressure is a new finding alongside these kinds of symptoms, the heart is a likely suspect.
The Vasovagal Response and Fainting
If you’ve ever fainted at the sight of blood, during a painful medical procedure, or while standing in a hot, crowded room, you’ve experienced neurally mediated syncope. This is the single most common cause of fainting in otherwise healthy people.
Here’s what happens: a trigger, whether emotional stress, pain, prolonged standing, or even straining during a bowel movement, sends a signal through your nervous system that simultaneously slows your heart rate and relaxes your blood vessels. Blood pools in your legs, your brain loses its blood supply, and you pass out. In the seconds before a faint, nerve activity that normally keeps blood vessels tight essentially shuts off completely. The whole episode is your nervous system overreacting to a stimulus that shouldn’t cause this kind of response.
Common triggers include strong emotions, seeing blood, standing for long periods, sudden changes in posture, bladder distension, and gastrointestinal cramping. If you’ve fainted without a clear cause, a tilt table test can help sort out the diagnosis. During this test, you lie flat on a table that’s then tilted upright to simulate standing while a technician monitors your heart rate and blood pressure for up to 45 minutes. A positive result means your blood pressure drops and symptoms appear during the position change.
Pregnancy
Blood pressure commonly drops during pregnancy, particularly in the first and second trimesters. The reason is straightforward: pregnancy triggers a dramatic expansion of your circulatory system. Blood volume increases significantly, but your blood vessels also relax and widen to accommodate the growing demands of the placenta. This drop in vascular resistance lowers blood pressure, sometimes enough to cause dizziness or lightheadedness.
By around 20 weeks, the growing uterus can also compress the large vein that returns blood from the lower body to the heart, especially when lying on your back. This further reduces the amount of blood reaching the heart and can cause a noticeable pressure drop. Blood pressure typically returns to its pre-pregnancy level in the third trimester or shortly after delivery.
Endocrine and Nervous System Disorders
Several hormonal conditions affect blood pressure regulation. An underactive thyroid slows your heart rate and can lower blood pressure. Adrenal insufficiency, where the adrenal glands don’t produce enough of the hormones that help regulate salt and fluid balance, is another well-known cause. Low blood sugar can also trigger a temporary drop.
Nervous system conditions like Parkinson’s disease and a related condition called multiple system atrophy damage the nerves that control blood vessel tightening. This makes it especially hard for the body to maintain blood pressure during position changes. Diabetes can cause similar nerve damage over time, which is one reason diabetic patients are at higher risk for blood pressure drops.
Blood Pressure Drops After Eating
Postprandial hypotension is a blood pressure drop that occurs within one to two hours after a meal. Normally, when blood rushes to your digestive system after eating, your heart speeds up slightly and blood vessels elsewhere in your body tighten to compensate. In some people, this compensation fails: the heart doesn’t speed up enough and the blood vessels don’t constrict properly, so pressure falls.
This is overwhelmingly a condition of older adults. Roughly 40% of people between ages 65 and 86 experience it to some degree. It’s more common if you also have high blood pressure, diabetes, Parkinson’s disease, heart failure, or kidney disease. Eating smaller, more frequent meals and limiting high-carbohydrate foods can reduce the severity of these episodes.
Severe Infections and Allergic Reactions
Two of the most dangerous causes of low blood pressure are sepsis and anaphylaxis. Both cause a form of circulatory collapse called distributive shock, where blood vessels throughout the body suddenly relax and widen. This causes blood pressure to plummet because the vessels can no longer maintain enough resistance to push blood to vital organs. At the same time, the smallest blood vessels become leaky, allowing fluid to seep out of the circulation and worsening the pressure drop.
Septic shock develops when a bacterial infection spirals out of control and the body’s immune response triggers widespread inflammation. Anaphylactic shock is the same basic mechanism driven by a severe allergic reaction, commonly to foods like peanuts, insect stings, or medications. Both are life-threatening emergencies. The warning signs are a sudden drop in blood pressure, confusion, rapid breathing, and skin that feels cool or clammy.
When Low Blood Pressure Becomes Dangerous
A low reading on its own isn’t necessarily a problem. Many people, particularly younger women and athletes, walk around with blood pressure well below 90/60 and feel perfectly fine. Low blood pressure only matters when it causes symptoms or when it signals an underlying condition.
The symptoms to pay attention to are dizziness or lightheadedness, fainting or near-fainting, blurred vision, nausea, fatigue, and difficulty concentrating. These indicate that your brain isn’t getting adequate blood flow. Symptoms that come on suddenly, especially alongside confusion, cold skin, rapid shallow breathing, or a weak pulse, suggest a more serious cause like shock and require emergency care. Chronic, milder symptoms that worsen with standing or after meals point toward the more manageable causes described above and are worth investigating with your doctor, particularly if they’re affecting your daily life.