Merck Manual

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Some Causes and Features of Constipation

Some Causes and Features of Constipation


Examples/Common Features*


Acute constipation‡

Twisting of a loop of intestine (volvulus), hernia, adhesions, and fecal impaction

Usually vomiting, crampy abdominal pain, and a distended abdomen

Abdominal x-rays

Sometimes CT

Major acute illness, such as sepsis (a severe infection of the bloodstream)

Immediately after abdominal surgery

Recent head or spinal cord injury

Prolonged bed rest

Abdominal x-rays


Drugs with anticholinergic effects, such as antihistamines, some antidepressants, antipsychotic drugs, drugs used to treat Parkinson disease, and drugs that reduce or stop muscle spasms in the digestive tract (antispasmodic drugs)

Drugs containing certain metals (iron, aluminum, calcium, barium, or bismuth)


Calcium channel blockers

Usually constipation that begins shortly after starting a new drug

A doctor's examination to exclude other causes of constipation

Sometimes stopping the drug to see whether constipation resolves

Chronic constipation‡

Often constipation that has recently developed, persists for weeks, and gradually worsens as the tumor grows

Sometimes blood in stool (blood may be visible or detected during a doctor's examination)

Metabolic disorders

Blood tests

Central nervous system disorders (affecting the brain or spinal cord)

MRI and/or CT

Peripheral nervous system disorders (affecting nerves outside the brain and spinal cord)

A doctor’s examination

Sometimes x-rays after barium is inserted in the rectum (barium enema) and/or biopsy

Dyssynergic defecation (dysfunction affecting nerves and muscles in the pelvis that coordinate defecation)


Needing to use fingers to have a bowel movement

Pressure measurements of the anus and rectum (anorectal manometry)

Systemic disorders

A doctor’s examination

Sometimes biopsy and/or blood tests

Functional disorders

Often a sense of a blockage in the anus and/or rectum, prolonged or difficult defecation, or excessive straining

A doctor’s examination

Sometimes sigmoidoscopy

Dietary factors

Low-fiber diet or chronic laxative abuse

A doctor’s examination alone

* Features include symptoms and the results of the doctor's examination. Features mentioned are typical but not always present.

† Although a doctor's examination is always done, it is mentioned in this column only if the diagnosis can sometimes be made by the doctor's examination alone, without any testing.

‡ There is some overlap between causes of acute and chronic constipation. In particular, drugs are common causes of both.

CT = computed tomography; MRI = magnetic resonance imaging.