Merck Manual

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Some Causes of Low Blood Pressure

Some Causes of Low Blood Pressure

What Happens in the Body

Examples of Causes

The autonomic nervous system becomes impaired

Blood flow back to the heart is blocked

During pregnancy, pressure on the inferior vena cava (the main vein that carries blood from the legs) from the uterus when women lie in certain positions

Increased abdominal pressure when straining to move bowels or pass urine or when lifting heavy weights

Blood vessels become dilated (widened)

Alcohol

Some allergic reactions

Some antidepressants, such as amitriptyline

Antihypertensive drugs that dilate blood vessels (such as calcium channel blockers, angiotensin-converting enzyme inhibitors, and angiotensin II receptor blockers)

Bacterial infections, if severe

Exposure to heat

Nerve damage (such as that due to diabetes, amyloidosis, or spinal cord injuries)

Nitrates

Blood volume is decreased

Diarrhea

Diuretics (drugs that help the kidneys remove water from the body, such as furosemide and hydrochlorothiazide)

Excessive bleeding

Excessive sweating

Excessive urination (a common symptom of untreated diabetes or Addison disease)

The brain centers that control blood pressure are inhibited

Alcohol

Antidepressants

Antihypertensive drugs such as methyldopa and clonidine

Barbiturates

Cardiac output is decreased

Heart muscle damage or malfunction (such as that due to a heart attack or myocarditis)