Blood pressure is considered low when it falls below 90/60 mmHg. This can happen for a wide range of reasons, from something as simple as not drinking enough water to underlying heart or hormonal conditions. For many people, naturally low blood pressure causes no symptoms and isn’t a problem. It only becomes a concern when it drops enough to reduce blood flow to your organs, causing dizziness, fainting, or fatigue.
Dehydration and Blood Volume
One of the most common and straightforward causes of low blood pressure is dehydration. When your body doesn’t have enough water, the total volume of blood in your circulatory system drops. Less blood means less pressure pushing against your artery walls. This is why blood pressure often dips during hot weather, after intense exercise, or during an illness that causes vomiting or diarrhea. Significant blood loss from an injury or surgery works the same way, reducing the volume your heart has to pump.
As a general daily target, men need roughly 125 ounces (3.7 liters) of fluid and women need about 91 ounces (2.7 liters). If you’re physically active, live in a warm climate, or are recovering from illness, you likely need more. Simply increasing your fluid intake can be enough to bring mildly low readings back up.
Pregnancy
Blood pressure commonly drops during pregnancy, especially in the first and second trimesters. The reason is that pregnancy hormones cause blood vessels to expand rapidly, which lowers the pressure inside them. Your body is also diverting blood flow to the uterus and placenta. For most pregnant women, this is temporary and normal. Blood pressure typically returns to pre-pregnancy levels after delivery.
Drops After Standing or Eating
If your blood pressure drops specifically when you stand up, that’s called orthostatic hypotension. A drop of 20 mmHg or more in your systolic (top) number, or 10 mmHg or more in your diastolic (bottom) number, within a few minutes of standing meets this threshold. Gravity naturally pulls blood into your legs and abdomen when you rise. Normally, specialized pressure-sensing cells near your heart and neck arteries detect this shift and signal your brain to speed up your heart rate and tighten blood vessels, correcting the drop almost instantly. Orthostatic hypotension happens when that corrective process is too slow or doesn’t work properly.
A related pattern is blood pressure that drops after meals, which is more common in older adults. Digestion requires a large supply of blood to the gut. In some people, the body can’t compensate fast enough, and pressure falls noticeably 15 to 45 minutes after eating. Smaller, more frequent meals and staying hydrated around mealtimes can help.
Medications That Lower Blood Pressure
Several common medications can push blood pressure too low, sometimes intentionally and sometimes as an unwanted side effect. The most frequent culprits include:
- Blood pressure medications: If you take drugs for high blood pressure, your dose may be bringing your numbers down further than intended.
- Diuretics (water pills): These reduce fluid volume in your body, which directly lowers pressure.
- Nitrate medications: Often prescribed for chest pain, these relax and widen blood vessels.
- Certain antidepressants: Older tricyclic antidepressants are particularly known for causing drops in blood pressure upon standing.
- Antipsychotic medications: Especially older-generation drugs in this class.
- Medications for erectile dysfunction, heart failure, or weight loss: These can also contribute to lower readings.
If you suspect your medication is the cause, don’t stop taking it on your own. A dose adjustment or switch to a different drug is often all that’s needed.
Heart Problems
Your heart is the pump driving your blood pressure. When it can’t pump effectively, pressure drops. A very slow heart rate (bradycardia) is one example. If your heart rate falls into the 30s, your brain may not get enough oxygen, leading to fainting, lightheadedness, and shortness of breath. This can happen when the heart’s natural pacemaker malfunctions or when electrical signals have trouble traveling between the upper and lower chambers of the heart.
Heart valve problems can also play a role. Damaged or narrowed valves restrict blood flow, reducing the volume your heart pushes out with each beat. Heart failure, where the heart muscle is weakened and can’t pump forcefully enough, is another cause of persistently low blood pressure.
Hormonal and Endocrine Causes
Your adrenal glands, which sit on top of your kidneys, produce hormones that are essential for blood pressure regulation. Cortisol helps control blood pressure directly. Another adrenal hormone, aldosterone, manages the balance of sodium and potassium in your blood, which in turn controls how much salt and water your body retains. When the adrenal glands don’t produce enough of these hormones (a condition called adrenal insufficiency, or Addison’s disease in its primary form), blood pressure can fall significantly. In severe cases, called an adrenal crisis, the lack of cortisol can cause dangerously low blood pressure along with low blood sugar and sodium imbalances.
Thyroid disorders can also contribute. An underactive thyroid slows many body processes, including heart rate and the tone of blood vessel walls, both of which can lower blood pressure.
Nutrient Deficiencies and Anemia
Your body needs adequate vitamins B12 and folate to produce healthy red blood cells. When you’re deficient in either, your bone marrow produces fewer and abnormally large red blood cells that don’t carry oxygen efficiently. This type of anemia reduces the oxygen-carrying capacity of your blood. With fewer functional red blood cells circulating, your cardiovascular system may struggle to maintain normal pressure, particularly during physical activity or when standing.
Common Symptoms to Recognize
Low blood pressure doesn’t always cause noticeable symptoms. When it does, the most common signs include dizziness or lightheadedness, especially upon standing; blurred vision; fatigue or general weakness; nausea; and fainting. These happen because your brain and other organs aren’t getting enough blood flow. Symptoms that come and go with position changes (like standing up quickly) point toward orthostatic hypotension specifically.
When Low Blood Pressure Becomes Dangerous
There’s an important difference between blood pressure that runs a little low and a medical emergency. A systolic reading below 90 mmHg with signs that your organs aren’t getting enough blood, such as confusion, cold or clammy skin, rapid breathing, or very low urine output, suggests your body is moving toward shock. Shock isn’t defined by a number alone. It’s defined by whether your organs are actually being deprived of blood flow. You can have a systolic pressure in the 80s and feel fine, or have a reading of 95 and be in serious trouble if your organs aren’t being perfused properly.
Practical Ways to Manage Low Blood Pressure
For chronic, mildly low blood pressure, several simple strategies can make a real difference. Staying well hydrated is the foundation. Adding a bit more salt to your diet can also help, since sodium pulls water into your blood vessels and increases blood volume. This is one of the few situations where extra sodium is actually beneficial.
Compression stockings are another practical tool. The gentle pressure they apply to your lower legs helps prevent blood from pooling there, and they can raise your blood pressure by about 5 to 10 mmHg. Standing up slowly, especially first thing in the morning or after sitting for a long time, gives your body a chance to adjust before gravity pulls blood downward. Eating smaller meals more frequently can help if your pressure tends to drop after eating.
If your low blood pressure is caused by an underlying condition like adrenal insufficiency, thyroid problems, or a heart rhythm issue, treating that condition directly is what will bring your numbers back to a healthier range.