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Theoretically, constipation can be caused by the slow passage of digesting food through any part of the intestine. More than 95% of the time, however, the slowing occurs in the colon.

Medications

A frequently overlooked cause of constipation is medications. The most common offending medications include:

  • Narcotic pain medications such as codeine (for example, Tylenol #3), oxycodone (for example, Percocet), and hydromorphone (Dilaudid);
  • Antidepressants such as amitriptyline (Elavil) and imipramine (Tofranil)
  • Anticonvulsants such as phenytoin (Dilantin) and carbamazepine (Tegretol)
  • Iron supplements
  • Calcium channel-blocking drugs such as diltiazem (Cardizem) and nifedipine (Procardia)
  • Aluminum-containing antacids such as Amphojel and Basaljel

In addition to the medications listed above, there are many others that can cause constipation. Simple measures (for example, increasing dietary fiber) for treating the constipation caused by medications often are effective, and discontinuing the medication is not necessary. If simple measures don't work, it may be possible to substitute a less-constipating medication. For example, a nonsteroidal antiinflammatory drug (for example, ibuprofen) may be substituted for narcotic pain medications. Additionally, one of the newer and less constipating anti-depressant medications (for example, fluoxetine (Prozac)) may be substituted for amitriptyline and imipramine.

Habit

Bowel movements are under voluntary control. This means that the normal urge people feel when they need to have a bowel movement can be suppressed. Although occasionally it is appropriate to suppress an urge to defecate (for example, when a bathroom is not available), doing this too frequently can lead to a disappearance of urges and result in constipation.

Diet

Fiber is important in maintaining a soft, bulky stool. Diets that are low in fiber can, therefore, cause constipation. The best natural sources of fiber are fruits, vegetables, and whole grains.

Laxatives

One suspected cause of severe constipation is the overuse of stimulant laxatives [for example, senna (Senokot), castor oil, and certain herbs]. An association has been shown between the chronic use of stimulant laxatives and damage to the nerves and muscles of the colon, and it is believed by some that the damage is responsible for the constipation. It is not clear, however, whether the laxatives have caused the damage or whether the damage existed prior to the use of laxatives and, indeed, has caused the laxatives to be used. Nevertheless, because of the possibility that stimulant laxatives can damage the colon, most experts recommend that stimulant laxatives be used as a last resort after non-stimulant treatments have failed.

Hormonal disorders

Hormones can affect bowel movements. For example:

  • Too little thyroid hormone (hypothyroidism) and too much parathyroid hormone (by raising the calcium levels in the blood) can cause constipation.
  • At the time of a woman's menstrual periods, estrogen and progesterone levels are high and may cause constipation. However, this is rarely a prolonged problem.
  • High levels of estrogen and progesterone during pregnancy also can cause constipation.

Diseases that affect the colon

There are many diseases that can affect the function of the muscles and/or nerves of the colon. These include diabetes, scleroderma, intestinal pseudo-obstruction, Hirschsprung's disease, and Chagas disease. Cancer or narrowing (stricture) of the colon that blocks the colon likewise can cause a decrease in the flow of stool.

Central nervous system diseases

A few diseases of the brain and spinal cord may cause constipation, including Parkinson's disease, multiple sclerosis, and spinal cord injuries.

Colonic inertia

Colonic inertia is a condition in which the nerves and/or muscles of the colon do not work normally. As a result, the contents of the colon are not propelled through the colon normally. The cause of colonic inertia is unclear. In some cases, the muscles or nerves of the colon are diseased. Colonic inertia also may be the result of the chronic use of stimulant laxatives as described above. In most cases, however, there is no clear cause for the constipation.

Pelvic floor dysfunction

Pelvic floor dysfunction (also known as outlet obstruction or outlet delay) refers to a condition in which the muscles of the lower pelvis that surround the rectum (the pelvic floor muscles) do not work normally. These muscles are critical for defecation (bowel movement). It is not known why these muscles fail to work properly in some people, but they can make the passage of stools difficult even when everything else is normal.

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Archived: March 20, 2014

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