Hypotension is the medical term for low blood pressure, generally defined as a reading below 90/60 mmHg. While high blood pressure gets most of the attention, blood pressure that drops too low can also cause problems, from mild dizziness to fainting to, in extreme cases, organ damage. That said, many people naturally run on the lower end of the blood pressure spectrum and feel perfectly fine. Low blood pressure is only considered a medical concern when it causes noticeable symptoms.
How Blood Pressure Is Measured
A blood pressure reading has two numbers. The top number (systolic) measures the force of blood against artery walls when the heart beats. The bottom number (diastolic) measures that force between beats, when the heart is resting. Normal blood pressure falls between 90/60 and 120/80 mmHg. Hypotension can be diagnosed when the systolic pressure drops below 90, the diastolic falls under 60, or both.
What Low Blood Pressure Feels Like
When blood pressure drops low enough to reduce blood flow to the brain and other organs, you may notice dizziness, lightheadedness, blurred vision, nausea, fatigue, or difficulty concentrating. Some people feel unsteady on their feet or experience brief fainting episodes. These symptoms tend to come on suddenly, especially when standing up, and often improve once you sit or lie down.
The reason these symptoms center on the brain is straightforward: your brain sits at the top of your body and depends on steady blood flow to function. Normally, blood vessels throughout the body tighten automatically to maintain pressure and keep blood flowing upward. When that system falters, the brain is the first organ to feel the effects. In sudden drops, the brain’s built-in pressure regulation simply can’t adjust fast enough to compensate.
Common Causes
Low blood pressure has a wide range of causes, from everyday situations to serious medical conditions. Dehydration is one of the most common triggers. When your body loses more fluid than it takes in (through sweating, vomiting, diarrhea, or simply not drinking enough), blood volume drops and pressure falls with it.
Heart conditions that reduce the heart’s pumping ability, such as heart failure, valve problems, or a very slow heart rate, can also lower blood pressure. Endocrine disorders like thyroid disease and adrenal insufficiency affect the hormones that help regulate blood pressure. Severe infections, significant blood loss, and severe allergic reactions can all cause dangerous, rapid drops in pressure.
Medications
Several common medication classes lower blood pressure as a side effect. Diuretics (water pills) increase sodium loss through urine and can deplete blood volume, particularly in older adults. Blood pressure medications like alpha-blockers and beta-blockers reduce vascular resistance or slow the heart’s compensatory responses when you change position. Nitrates, used for chest pain, relax blood vessels and decrease the volume of blood returning to the heart.
Medications for mental health conditions are also frequent culprits. Tricyclic antidepressants cause low blood pressure in 10 to 50 percent of patients who take them, and newer antidepressants like SSRIs roughly double the risk as well. Antipsychotic medications cause drops in blood pressure in up to 40 percent of patients. Even benzodiazepines, commonly prescribed for anxiety, can impair the body’s ability to maintain pressure when you stand.
Orthostatic Hypotension
Orthostatic hypotension is the type most people have experienced at least once: that head rush when you stand up too quickly. It’s formally defined as a drop of at least 20 mmHg in systolic pressure or 10 mmHg in diastolic pressure within three minutes of standing. When you go from lying down to standing, gravity pulls blood toward your legs. Normally, your body compensates within seconds by tightening blood vessels and slightly increasing heart rate. When that reflex is sluggish or impaired, blood pressure drops and you feel dizzy or faint.
Orthostatic hypotension becomes more common with age as the reflexes that regulate blood pressure slow down. It’s also more likely if you’re dehydrated, taking certain medications, or have a condition that affects the nervous system, such as Parkinson’s disease or diabetes.
Postprandial Hypotension
Some people experience a noticeable blood pressure drop after eating. Digestion requires extra blood flow to the stomach and intestines. To compensate, the heart normally beats a little faster and blood vessels elsewhere in the body tighten. When those adjustments don’t happen efficiently, blood pressure falls. This is called postprandial hypotension, and it’s surprisingly common in older adults. Studies show that roughly 40 percent of people between ages 65 and 86 experience it.
Your risk of postprandial hypotension 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 blood pressure drop after eating.
Vasovagal Syncope
Vasovagal syncope is the most common cause of fainting, and it results from a sudden, temporary drop in blood pressure. It happens when the nervous system overreacts to certain triggers: standing for long periods, heat exposure, the sight of blood, extreme emotional distress, or even straining during a bowel movement. The body essentially sends a mixed signal, causing blood vessels to widen and heart rate to slow at the same time. Blood pressure plummets, the brain briefly loses adequate blood flow, and you faint.
Vasovagal episodes are usually harmless, though falling during a faint can cause injury. Most people recover fully within a few minutes of lying down, as blood flow to the brain quickly returns to normal.
Managing Low Blood Pressure
If low blood pressure isn’t causing symptoms, it typically doesn’t need treatment. For people who do experience symptoms, management often starts with simple lifestyle changes. Increasing fluid intake and adding salt to your diet can help expand blood volume. For orthostatic hypotension specifically, clinical guidelines recommend 10 to 20 grams of salt per day, which is significantly higher than what most people normally consume. This level of salt intake should only be done under medical guidance, since it would be harmful for someone with high blood pressure or heart failure.
Compression garments can also make a meaningful difference. An abdominal binder applying 15 to 20 mmHg of pressure raised standing blood pressure by about 11/6 mmHg in laboratory testing, a clinically significant improvement for someone prone to dizziness. Compression stockings work on a similar principle by preventing blood from pooling in the legs.
Other practical strategies include standing up slowly, especially first thing in the morning. Sleeping with the head of the bed slightly elevated can train the body to tolerate upright positions better. Avoiding alcohol and large, carbohydrate-heavy meals helps prevent the blood pressure drops that follow both. Crossing your legs while standing or squeezing your thigh muscles can provide a quick boost in blood pressure when you feel symptoms coming on.
When Low Blood Pressure Becomes Dangerous
In most cases, low blood pressure is more of a nuisance than a danger. But a sudden, severe drop in blood pressure can lead to shock, a life-threatening condition in which organs don’t receive enough oxygen. Signs of shock include cool and clammy skin, pale or ashen appearance, a blue or gray tinge to the lips or fingernails, rapid and shallow breathing, a racing pulse, confusion, and loss of consciousness.
Shock can result from severe bleeding, a serious infection, a major allergic reaction, or a heart attack. Without treatment, it can cause permanent organ damage or death. If someone shows signs of shock, calling emergency services immediately is critical. While waiting for help, having the person lie down with their legs elevated (if no spinal injury is suspected) helps direct blood flow toward vital organs.