Low blood pressure, defined as a reading below 90/60 mmHg, can be a sign of anything from dehydration and medication side effects to heart problems, hormonal disorders, and pregnancy. For many people it causes no symptoms and isn’t a concern. But when it produces dizziness, fainting, or fatigue, it often points to something specific going on in the body that deserves attention.
Dehydration and Low Fluid Volume
One of the most common reasons blood pressure drops is simply not having enough fluid in the bloodstream. When you’re dehydrated from illness, excessive sweating, vomiting, or diarrhea, there’s less blood volume for your heart to pump. That means less pressure pushing against your artery walls. Severe blood loss from an injury or internal bleeding works the same way, reducing the volume of circulating blood and causing pressure to fall, sometimes dangerously fast.
Mild dehydration might only cause lightheadedness when you stand up. But significant fluid loss can progress to shock, where organs stop getting enough oxygen. Signs include cool or pale skin, a weak and rapid pulse, fast shallow breathing, and confusion or altered mental status. This is a medical emergency.
Heart Conditions
Your heart is the pump behind your blood pressure, so problems with the heart itself commonly show up as low readings. A very slow heart rate, known as bradycardia (fewer than 60 beats per minute), means the heart isn’t pushing blood out frequently enough to maintain normal pressure. Bradycardia can result from aging-related damage to heart tissue, a previous heart attack, inflammation of the heart muscle, congenital heart defects, or complications from heart surgery.
Heart valve problems also play a role. When valves don’t open or close properly, blood flow becomes inefficient, and pressure drops. Heart failure, where the heart can’t pump strongly enough to meet the body’s needs, is another cause. Any of these conditions can produce fatigue, shortness of breath, and fainting spells alongside low blood pressure readings.
Hormonal and Endocrine Disorders
Your adrenal glands sit on top of your kidneys and produce hormones that directly regulate blood pressure. In adrenal insufficiency (Addison’s disease), these glands don’t make enough cortisol or aldosterone. Cortisol helps control blood pressure, while aldosterone manages the balance of sodium and potassium in your blood, which in turn controls salt and water balance. When both hormones are low, blood pressure can drop significantly. During an adrenal crisis, the severe lack of cortisol can cause life-threatening low blood pressure along with dangerously low blood sugar and sodium.
An underactive thyroid is another endocrine cause. Hypothyroidism slows many body processes, including heart rate, and is actually listed as a direct cause of bradycardia. The result is the same: a slower heart pumps less blood per minute, and pressure falls.
Medications
Low blood pressure is a well-known side effect of several drug classes, and it’s one of the most fixable causes. All blood pressure medications can overshoot their goal and drop pressure too low. This includes diuretics (water pills), beta blockers, and alpha blockers. If your dose was recently adjusted and you’re feeling dizzy or faint, the medication is a likely culprit.
Other medications that can lower blood pressure include Parkinson’s disease drugs, tricyclic antidepressants, and erectile dysfunction medications. The risk increases when erectile dysfunction drugs are combined with nitroglycerin, a heart medication, because both relax blood vessels and the combined effect can cause a steep pressure drop.
Blood Pressure Drops After Eating
Postprandial hypotension is a blood pressure drop that happens within one to two hours of eating a meal. Normally, your heart rate speeds up after eating to supply your digestive system with extra blood, while blood vessels elsewhere in the body tighten to compensate. When those adjustments don’t happen properly, pressure falls.
This is especially common in older adults. Research shows roughly 40% of people between ages 65 and 86 experience postprandial hypotension. Risk factors include high blood pressure (paradoxically), diabetes, Parkinson’s disease, heart failure, and end-stage kidney disease. If you consistently feel lightheaded or unsteady after meals, this pattern is worth tracking and discussing with your doctor.
Pregnancy
Low blood pressure during pregnancy is normal and expected. Blood pressure begins dropping early, around 6 to 8 weeks of gestation, and reaches its lowest point during the second trimester, typically falling 5 to 10 mmHg below pre-pregnancy levels. This happens because the circulatory system expands rapidly to supply the growing placenta, and blood vessels relax in response to hormonal changes.
Pressure gradually rises again during the third trimester and returns close to pre-pregnancy levels after delivery. While this dip can cause dizziness, especially when standing up quickly, it’s a normal part of cardiovascular adaptation during pregnancy rather than a sign of a problem.
Orthostatic Hypotension
If your blood pressure drops primarily when you stand up from sitting or lying down, that’s called orthostatic hypotension. It affects an estimated 7% to 10% of adults with high blood pressure, particularly older adults, and is linked to a higher risk of cardiovascular events over time. The cause can be neurological (your nervous system isn’t signaling blood vessels to tighten quickly enough), medication-related, or tied to dehydration. It’s not a diagnosis on its own but a pattern that points toward one of the underlying causes described above.
Nutritional Deficiencies
Deficiencies in vitamin B12 and folate can cause a type of anemia where the body produces red blood cells that are too large and don’t function properly. These oversized cells are less able to carry oxygen throughout the body. When your tissues aren’t getting adequate oxygen, the cardiovascular system is under strain, and blood pressure may drop. Iron deficiency anemia works similarly, reducing the blood’s oxygen-carrying capacity and potentially lowering pressure.
When Low Blood Pressure Becomes Dangerous
Low blood pressure without symptoms is generally harmless. Some people naturally run readings below 90/60 and feel perfectly fine. The concern starts when low pressure causes noticeable symptoms like dizziness, blurred vision, nausea, fatigue, or difficulty concentrating. These suggest your brain and organs aren’t getting enough blood flow.
The most serious consequence of very low blood pressure is shock, where organs begin to fail from lack of oxygen. Warning signs include cold, pale, or clammy skin, a rapid but weak pulse, fast breathing, confusion or disorientation, and extreme weakness. Early shock can actually present with normal or even elevated blood pressure and heart rate, so the physical symptoms matter more than the number on the cuff. Without treatment, hypotension and a racing heart typically follow.