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

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)


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


Blood volume is decreased


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

Excessive bleeding

Excessive sweating

The brain centers that control blood pressure are inhibited


Antidepressants (some)

Antihypertensive drugs such as methyldopa and clonidine


Cardiac output is decreased