Constipation is a common problem that most people experience at some time in their life. If simple lifestyle measures aren't adequate to get things moving, several medications can help.

Stool softeners help to reduce the amount of straining necessary to move the bowels. Fiber plus water is the simplest example. Be sure to drink plenty of water, because fiber alone can actually worsen constipation. Docusate (sold as Colace® and other brand names) is also effective and can be safely taken 2-4 times daily. Mineral oil may also be helpful, and can be taken either orally or as an enema up to 1 time daily. These medications are safe for chronic daily use. The most significant potential side effect is excessively soft or even runny stool.

Laxatives work either by increasing bowel activity (irritant laxatives) or by increasing the water content of the stool (osmotic laxatives). Most laxatives can be taken either orally or rectally. In cases of severe constipation, or when there is concern about a possible intestinal obstruction, it is best to start with an enema or suppository to soften things up, and then, if necessary, add an oral laxative to keep things going.

Some laxatives are safer than others for long-term use, but all of them can cause serious side effects. And please: Never use laxatives in an attempt to lose weight. They will not reduce your body fat, and can cause severe health problems when overused.

The two main irritant laxatives are senna and bisacodyl, which are available under a variety of brand names, in both orally and rectally administered forms. Their most common side effects are cramping, pain, urgent need to pass stool, and diarrhea. Chronic, repetitive use of irritant laxatives can cause electrolyte imbalances (especially low potassium levels) and dehydration. In addition, long-term daily use of these products might result in dependency, which can make it very difficult to stop using them.

Magnesium is an electrolyte that is poorly absorbed from the intestines, and therefore draws water into the stool, acting as an osmotic laxative. Milk of Magnesia® is available over the counter. Others, such as magnesium citrate or magnesium sulfate, require a prescription and might be a little stronger. Common side effects of magnesium-containing laxatives include cramps, nausea, bloating, and diarrhea. Patients with reduced kidney function should avoid this type of laxative because of the risk of elevated blood levels of magnesium.

Polyethylene glycol, or PEG, (MiraLax®, GlycoLax®, and other brand names) is another effective osmotic laxative, which recently became available without a prescription. Some of you may recognize PEG as the main ingredient in automotive antifreeze, but don't worry — PEG is actually a generic term for several different types of chemicals, and the one used as a laxative is very different from the antifreeze in your car's cooling system!

Lactulose and sorbitol, complex sugars that our bodies cannot digest, are 2 osmotic laxatives that require a prescription. Since they are not digested or absorbed, they do not raise blood sugar levels and are safe for diabetics (as are most other laxatives).

Sodium phosphate (e.g., Fleet® enema) and glycerin are over-the-counter osmotic laxatives that are typically administered rectally.

All of the osmotic laxatives can cause cramps, abdominal pain, nausea, or diarrhea, and, if used excessively, they can also cause dehydration. They generally don't cause as much electrolyte imbalance as the irritant laxatives, and are probably safer than the irritant laxatives for long-term use.

So, what's the best treatment for occasional constipation? Here's my advice:

1. Start with increased levels of physical activity and fiber, along with lots of water. 
2. If nothing happens, the first medicine to use is docusate, 1 to 2 times daily.
3. If docusate doesn't do the trick, try an over-the-counter osmotic laxative such as magnesium or PEG, once daily. Try to be patient — this regimen often takes several days to clear the initial constipation.
4. If 3 to 4 days of this treatment do not suffice, continue the osmotic laxative and add on an irritant laxative once daily, either orally or rectally, until stool is evacuated.
5. If all of this is still ineffective, or if you develop rectal bleeding or severe abdominal pain, then it is time to see a medical specialist.

Here's my approach for chronic constipation:

1. Use fiber, water, and a stool softener daily to keep chronic constipation under control.
2. I suggest using a laxative whenever 1 or 2 days go by without passing stool. This will minimize the chance of developing severe constipation. 
3. When you do become constipated, you can probably safely take PEG or some other osmotic laxative every day, if necessary.
4. Irritant laxatives can be added when necessary, but they probably should not be used more than 2 or 3 times per week.

For people with very severe and chronic constipation, a prescription medicine called lubiprostone (Amitiza®) has been available since 2006. This drug increases both the fluid content of the stool and the motility of the intestines. Side effects are similar to most other laxatives.

Lubiprostone does not appear likely to cause electrolyte imbalances or dependency, but it has only been on the market for a few years, so we don't yet know about its long-term safety. This is why lubiprostone should be reserved for patients who don't respond adequately to any of the older, more standard treatments.