Constipation is not having a bowel movement as often as you usually do, or having a tough time going because the stool is hard and dry. It's a very common problem, and usually happens because a person's diet doesn't include enough fluids and fiber.
Constipation usually isn't a cause for concern — it's preventable and most cases can be resolved with healthy eating and exercise habits.
After you chew and swallow food, it heads to your stomach. From there, it's on to the small intestine, then the large intestine (or bowels), and finally out of the body through the rectum and anus.
As food moves through your digestive system, your body soaks up water and nutrients it needs from the food. What's left over comes out as stool. Normal stool is usually soft and easy to pass, and it generally shouldn't be too difficult to have a bowel movement. But sometimes the bowels just don't move like they should.
A person is considered constipated when he or she has had fewer than three bowel movements in a week; when the stools are hard, dry, and unusually large; or when it's hard for the person to have a bowel movement.

Sign & Symptoms

Not having a bowel movement every day doesn't necessarily mean you're constipated. You likely have constipation, however, if you experience two of the following signs or symptoms:

• Pass fewer than three stools a week
• Experience hard stools
• Strain excessively during bowel movements
• Experience a sense of rectal blockage
• Have a feeling of incomplete evacuation after having a bowel movement
• Need to use manual maneuvers to have a bowel movement, such as finger evacuation or manipulation of your lower abdomen

What causes constipation?

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 over-looked 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 over-use 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.

Diagnosis & Investigation

Your doctor will take your medical history, perform a physical exam and ask about any prescription or over-the-counter medications you're taking. Your doctor will also want to rule out several conditions in diagnosing constipation. These include a blockage in your small intestine or colon (intestinal obstruction), a narrowing of the colon, an endocrine condition such as hypothyroidism, or an electrolyte disturbance, such as excessive calcium in the blood (hypercalcemia).
Extensive testing is usually reserved for people with severe symptoms. You may undergo these diagnostic procedures:

• Barium enema X-ray. In this test, the lining of your bowel is coated with a contrast dye (barium) so that your rectum, colon and sometimes a part of the small intestine can be clearly seen on an X-ray.
• Defecography. In this X-ray procedure, your doctor will fill your rectum with a soft paste with the same consistency as stool. As you expel the paste, X-rays are taken to evaluate the completeness of stool elimination and rectal muscle contractions.
• Sigmoidoscopy. In this procedure, your doctor inserts a lighted, flexible tube into your anus to examine your rectum and lower portion of your colon.
• Colonoscopy. This diagnostic procedure allows your doctor to examine the entire colon with a flexible, camera-equipped tube.
• Anorectal manometry. In this procedure, your doctor inserts a narrow, flexible tube into your anus and rectum, and then inflates a small balloon at the tip of the tube. The device is then pulled back through the sphincter muscle. This procedure allows your doctor to measure the coordination of the muscles you use to move your bowels.
• Marker studies or colorectal transit studies. In this procedure, you'll swallow a capsule containing markers that show up on X-rays taken over several days. Your doctor will look for signs of intestinal muscle dysfunction and how well food moves through the colon.

Treatments and Pharmacology

In most cases, simple changes in your diet and lifestyle will help relieve symptoms and manage constipation. Consider one or more of the following:
A high-fiber diet. A diet with at least 20 to 35 grams of fiber each day helps your body form soft, bulky stool. High-fiber foods include beans, whole grains and fresh fruits and vegetables. Limit foods that have little to no fiber, such as cheese, meat and processed foods.
Regular exercise. Physical activity will help stimulate intestinal activity.
Adequate fluid intake. Drinking plenty of water and other fluids will help soften your stool.
Take the time for bowel movements. Set aside sufficient time to allow for undisturbed visits to the toilet. And don't ignore the urge to have a bowel movement.
Laxatives. These over-the-counter medications should be considered as a last resort because they can become habit-forming. There are several different types of laxatives:

• Stimulants cause rhythmic contractions in the intestines. Examples include Correctol, Dulcolax and Senokot.
• Lubricants enable stool to move through your colon more easily. Examples include mineral oil and Fleet.
• Stool softeners moisten the stool and help prevent dehydration. Examples include Colace and Surfak.
• Fiber supplements, or bulk laxatives, are generally considered the safest of laxatives. Examples include FiberCon, Metamucil, Konsyl, Serutan and Citrucel. These agents must be taken with plenty of water.
• Osmotics help fluids to move through the colon. Examples include Cephulac, Sorbitol and Miralax.
• Saline laxatives act like a sponge to draw water into the colon for easier passage of stool. Examples include milk of magnesia and Haley's M-O.

Chloride channel activators. The agent lubiprostone (Amitiza) is available by prescription and increases fluid content of stool.
5-HT-4 agonists. These agents stimulate release of compounds in your body that increase fluid secretion in the intestines and decrease colonic transit time. Prucalopride is one such 5-HT-4 agonist.
If an underlying disorder is causing your constipation, treatment will be aimed at the specific cause. If pelvic floor dysfunction is the cause of your constipation, your doctor may suggest biofeedback as a treatment. This retraining technique may help you learn to better coordinate the muscles you use to have a bowel movement.
If you're pregnant and have constipation, try eating lots of high-fiber foods, such as fruits, vegetables and whole grains. Drink plenty of fluids and get as much exercise as you can. Swimming and walking may be good choices.
If your constipation doesn't respond to changes in lifestyle or medical treatment, surgical removal of part of your colon may be recommended. In this procedure, the problem segment or segments of the anal sphincter or rectum are removed.
Above all, recognize that a successful treatment program can take time and effort.