Normal Bowel Function

The function of the colon is to reabsorb water, store, and evacuate stool. About two quarts of fluid and residue enter the colon from the small bowel each day. The lining of the colon actively reabsorbs water and minerals, leaving a solid, formed stool. Stool is stored in the left side of the colon. Contractions in the sigmoid colon hold the stool above the rectum. When the colon fills with stool, the stool moves into the rectum. This is sensed as an urge to defecate, and one seeks a bathroom. The anal sphincter muscles relax and a wave of contraction in the colon pushes out a large amount of stool. This is termed a mass movement.

What is Constipation?

Constipation is a common problem with a variety of possible causes. This term may be used to describe several different symptoms. The normal frequency of stool passage is from three times a day to a movement every three days. Going more than three days without a bowel movement is therefore considered abnormal. Some people feel miserable if they do not defecate on a daily basis. Others may go a week or longer without any ill effects. Hard stools, straining to pass a bowel movement, or a sense of incomplete evacuation may also be termed constipation. If a person is uncomfortable as a result of bowel problems, then treatment is justified to relieve or minimize these symptoms.

What Tests Are Needed?

The duration of constipation and age of the patient are important factors in deciding which tests are needed to evaluate the patient with constipation. A change in bowel habit, especially in an older person, raises concern about the possibility of a blockage in the large bowel. This could be due to colon cancer or diverticulitis. Full evaluation with colonoscopy may be necessary to identify these disorders. This is especially important if there has been any rectal bleeding. Bleeding from hemorrhoids, fissures, and other benign causes cannot always be distinguished from bleeding from a polyp or cancer without actually looking into the colon.

Fiber Supplements

In many cases, the colon appears to be normal, but does not function normally. Most constipation can be easily corrected by the addition of a high fiber diet, or fiber supplements. More fiber increases the volume of the stool providing greater stimulation of the body’s natural reflexes.

The desired level of fiber intake is 20-30 grams per day. For most patients, the simplest and most palatable way to achieve this is with the addition of a high fiber cereal for breakfast each day. Insoluble fiber tends to be more effective than soluble fiber for patients with constipation.

Fiber supplements include products such as unprocessed wheat bran, psyllium (Metamucil, Effersyllium, Konsyl, Hydrocil), Benefiber (guar gum) and methylcellulose (Citrucel, FiberCon). These products vary widely in taste and texture. In order to be effective, fiber must be taken regularly, on a daily basis. When first beginning to take a fiber supplement, one should start with a small daily dose and gradually increase it over a period of several weeks. A large amount of fiber can sometimes cause gas and bloating if introduced too quickly.

Stool Softeners

Hard stools are another symptom associated with constipation. Stool softeners such as docusate (Surfak, Colace) may be helpful if fiber alone does not result in soft stools. Milk of magnesia or mineral oil may also be used in small doses for this purpose. Haley's M-O is a combination of mineral oil and milk of magnesia. Mineral oil should not be taken at bedtime as it can be regurgitated and sometimes can cause lung damage. Lactulose (Chronulac, Duphulac, Enulose) also works to soften stools. Prolonged, regular use of Milk of Magnesia can cause elevated magnesium levels and this can be toxic, especially in patients with poor kidney function.

Miralax is a powdered form of polyethylene glycol. This substance draws water into the colon to soften the stool and relieve constipation. It works very effectively and can be taken long term. It is not habit forming.

Laxative Dependence

Laxative dependence is a frequent problem associated with constipation. Ideally, constipation should be managed solely with fiber, and laxatives should rarely be used. Many patients find that a laxative is the only thing which will give them any relief. This is unfortunate as it makes it difficult to eliminate laxatives and the patient becomes dependent on laxatives.

Stimulant laxatives bypass normal reflexes involved in defecation. They work on the nerves and muscles in the colon. The result is strong contractions that push the stool out of the colon. With continued use, they gradually become less effective. Some examples of stimulant laxatives are senna, bisacodyl and cascara sagrada. Many herbal preparations contain various combinations of stimulants.

If a patient has been taking a stimulant laxative on a regular basis, it may be impossible to abruptly stop taking it. It may be necessary to continue a mild stimulant such as senna every night in addition to Miralax and adequate dietary fiber. Once a normal bowel habit has been established, the senna should be gradually tapered and eventually stopped completely.

Fecal Impaction

Some patients never seem to have a normal urge to have a bowel movement. This sensation or urge occurs due to the presence of stool distending the rectum. If this urge is ignored or suppressed, then it gradually goes away. This may occur in patients who are unable to go the bathroom when necessary. Fecal impaction, or a large plug of stool in the rectum which will not pass, may result. An impaction may be quite painful and can require urgent medical attention. A program of bowel retraining in this situation may require the use of glycerin suppositories or enemas in order to stimulate the body's normal reflexes to initiate a bowel movement.

Irritable Bowel Syndrome

Irritable bowel syndrome may be associated with constipation. This is often the result of spasm in the colon which blocks the passage of stool. Fiber supplements alone will correct the problem in many cases. Some patients may require specific medication to relieve spasm. Anticholinergic or antispasmodic drugs (Levsin, Bentyl, Donnatal, Librax) may be very helpful, especially if the constipation is associated with abdominal cramping.

Zelnorm is a new drug specifically indicated for women with irritable bowel and constipation. It is very potent and can sometimes even cause diarrhea.


Many drugs can cause constipation. Some of the more common ones include codeine and other narcotic pain medications. If constipation begins after starting a new medicine, consideration should be given to changing the drug. Please pay attention to all the drugs you are taking, including nutritional and dietary supplements. If there is any question, bring all your medications to the office for review.

Regular Habits

In order to have a regular bowel habit, one must be consistent with a treatment program and lifestyle measures. A regular pattern of diet, rest, and exercise, will improve the response to any therapy. Constipation usually develops gradually and also improves gradually. A patient, persistent approach is most likely to be successful.