Causes of Low Blood PressureUnderstanding Why Blood Pressure Drops

Low blood pressure (hypotension) can result from many different causes—some temporary and harmless, others indicating underlying health issues that need attention. Unlike high blood pressure, which is almost always problematic, low blood pressure is only concerning when it causes symptoms or indicates an underlying condition.

Understanding what's causing your low blood pressure helps determine whether it needs treatment and what approach might work best.

Common Causes

Dehydration

Dehydration is one of the most frequent causes of low blood pressure. When your body loses more fluid than it takes in, blood volume decreases, reducing the pressure in your arteries. Even mild dehydration can lower blood pressure noticeably.

Dehydration can result from inadequate fluid intake, excessive sweating (exercise, hot weather), vomiting, diarrhea, fever, or diuretic use. Older adults are particularly susceptible because the thirst mechanism becomes less sensitive with age.

Prolonged Standing or Sitting

Staying in one position for extended periods can cause blood to pool in the legs, temporarily reducing blood flow to the brain and lowering blood pressure. This is why some people feel lightheaded after standing at a concert or sitting through a long flight.

Sudden Position Changes

Orthostatic hypotension occurs when blood pressure drops suddenly upon standing. Normally, your body quickly compensates for position changes by constricting blood vessels and increasing heart rate. When this response is delayed or inadequate, you feel dizzy or lightheaded. This affects up to 20% of people over age 65.

After Eating

Postprandial hypotension is a blood pressure drop that occurs after meals, particularly large meals high in carbohydrates. Blood flow increases to the digestive system, and if the body doesn't compensate adequately, blood pressure falls. This primarily affects older adults and those with autonomic nervous system disorders.

Medication-Related Causes

Many medications can lower blood pressure as either their primary effect or a side effect.

Blood pressure medications: Drugs prescribed to lower high blood pressure can sometimes work too well, especially when dosages are adjusted or when combined with other factors like dehydration. Diuretics are particularly likely to cause low pressure by reducing blood volume.

Heart medications: Beta-blockers, calcium channel blockers, and other cardiac drugs affect blood pressure as part of their mechanism of action.

Parkinson's disease medications: Drugs used to treat Parkinson's, particularly dopamine agonists, commonly cause orthostatic hypotension.

Antidepressants: Tricyclic antidepressants and some other psychiatric medications can lower blood pressure, especially when standing.

Erectile dysfunction medications: Drugs like sildenafil (Viagra) dilate blood vessels and can cause significant blood pressure drops, especially if combined with nitrate medications.

Alpha-blockers: Used for prostate enlargement and sometimes hypertension, these medications can cause orthostatic hypotension.

Medical Conditions

Heart Problems

Various heart conditions can reduce blood pressure by affecting the heart's ability to pump effectively. Heart failure occurs when the heart can't pump enough blood to meet the body's needs. Extremely low heart rate (bradycardia) may not pump enough blood volume. Heart valve problems can impair blood flow. Heart attack can damage heart muscle and reduce pumping ability.

Endocrine Disorders

Adrenal insufficiency (Addison's disease) reduces production of hormones that help regulate blood pressure. Thyroid disorders—both hypothyroidism and hyperthyroidism—can affect blood pressure. Low blood sugar (hypoglycemia) can trigger a blood pressure drop along with other symptoms like shakiness and confusion.

Autonomic Nervous System Disorders

The autonomic nervous system controls automatic body functions, including blood pressure regulation. Conditions like Parkinson's disease, multiple system atrophy, and pure autonomic failure damage these regulatory mechanisms, often causing severe orthostatic hypotension.

Diabetes can damage autonomic nerves over time (diabetic autonomic neuropathy), impairing blood pressure regulation.

Blood Loss and Anemia

Significant blood loss—from trauma, surgery, or internal bleeding—directly reduces blood volume and pressure. Severe anemia (low red blood cell count) reduces the blood's oxygen-carrying capacity, which can lower blood pressure and cause symptoms similar to hypotension.

Severe Infections

Sepsis occurs when infection spreads to the bloodstream, triggering a severe inflammatory response that causes blood vessels to dilate dramatically and blood pressure to plummet. This is a life-threatening emergency.

Severe Allergic Reactions

Anaphylaxis is a severe allergic reaction that causes widespread blood vessel dilation and can drop blood pressure dangerously. It requires immediate emergency treatment with epinephrine.

Other Factors

Pregnancy

Blood pressure commonly drops during the first 24 weeks of pregnancy as the circulatory system expands rapidly. This is usually normal and resolves after delivery. However, significant symptoms should be reported to your healthcare provider.

Nutritional Deficiencies

Deficiencies in certain nutrients can contribute to low blood pressure. Vitamin B12 and folate deficiencies can cause anemia, which may lower blood pressure. Iron deficiency similarly causes anemia. Ensuring adequate nutrition helps maintain healthy blood pressure.

Genetic Factors

Some people naturally run lower blood pressure due to genetic factors. If you've always had low readings without symptoms, this may simply be your normal. Athletic individuals often have lower blood pressure due to cardiovascular efficiency.

Frequently Asked Questions