An enema is procedure used for clearing the bowel and colon of fecal matter. The enema introduces liquid, usually water and sodium bicarbonate or sodium phosphate, by means of a bulb or enema bag, into the anus and thus to the bowel and colon. This tends to stimulate the bowel to release fecal matter.

The enema can also mean introduction of any substances into the bloodstream via the anus. People with severe nausea are sometimes given an enema containing anti-nausea medication. Instead of the liquid form of the cleansing enema, this type of substance introduction is usually in the form of a suppository. People with high fevers and nausea may benefit from suppositories containing acetaminophen that can quickly bring down a fever because it reaches the blood stream more quickly. Suppository medications are commonly used in the UK, but are not quite as popular in the US.

An enema can be performed at home. People with bowel impaction or severe constipation might be told to use one. They are often available for purchase at local drug stores. Most people, unless constipation is exceptionally severe, prefer to benefit from using laxatives instead, which also result in clearing the bowel and colon through a much less uncomfortable procedure.

Some enemas still contain mineral oil, and this is not preferred by most people. Mineral oil may cause leakage of the bowel, which cannot be controlled, for up to a day after the enema is administered. The water-based enema is considered just as effective and it is easier to control bowel movements after the enema is given.

Certain medical tests may require the use of an enema. An enema may be standard procedure prior to a colonoscopy, since fecal matter can obscure the test. Also, some tests are performed using a barium enema. An enema containing barium, a radioactive substance, can help visualize the gastrointestinal tract and any possible problems. The barium enema is usually given right before x-rays of the intestines are taken.

It used to be quite common for pregnant women going into labor, or who were past their due date to have an enema. This was thought to provoke greater labor pains and speed labor. It was also thought more sanitary, since fecal matter would not be passed during strong contractions. This is seldom performed now, and was a source of discomfort to many women for numerous years. If any fecal matter is passed during labor and delivery it is simply quickly cleaned up.

Some people believe that occasional cleaning of the bowel through an enema promotes greater health, although there is little evidence that it is necessary as a part of an overall health regimen. This belief became popular at the advent of the 20th century, and some still adhere to it. People may have enemas performed as an alternative medicine procedure, in the belief that it will clear the body of toxins and strengthen the muscles of the colon.