How does a laxative work? There are several different types of laxative, and they all work in different ways. Some add bulk to the stool, some soften it by helping it hold more water, some lubricate it, some pull water into the bowel, and some stimulate the nerves and muscles in the intestine. There are natural laxatives and chemical laxatives as well. They also take different amounts of time to work, so the type used usually depends on the person’s situation and on what kind of constipation is causing the problem.
If everything is working normally, it usually takes between 24 and 72 hours for food to pass through the digestive system, although that can vary depending on what the food is made of and on the person eating it. Digestion begins as soon as food enters the mouth because saliva contains enzymes that start to break it down. The chewed food passes down the esophagus into the stomach, where stomach acid and more enzymes continue the job and turn it into a thick, soupy mixture called chyme. The chyme then moves into the small intestine, where most of the nutrients the body needs are absorbed through the intestinal wall and passed into the bloodstream. What remains then moves into the large intestine, which is actually shorter than the small intestine despite its name. In adults, the small intestine is around 6 meters long, while the large intestine is only around 1.5 to 2 meters long. It is called “large” because it is wider, not because it is longer.
By the time the food matter reaches the large intestine, most of the nutrients have already been taken out. The colon’s main job is to absorb more water and electrolytes and to prepare the waste for removal from the body. There are also trillions of bacteria living there, helping to break down the parts of food that we cannot digest by ourselves. As more water is absorbed, the remaining matter becomes firmer and more solid. It is then pushed along by a rhythmic wave of muscular contractions in the intestinal wall called peristalsis until it eventually leaves the body. If there is enough fiber in the diet, enough water in the system, and the bowel is moving at a reasonable speed, the journey from mouth to toilet usually happens without much trouble. Sometimes, though, the stool becomes too hard, too dry, or too slow-moving, and that is when laxatives can help.
Laxatives are substances that make it easier to pass stool. The first type works by adding bulk. These are called bulk-forming laxatives. They are often made from fiber-like substances that absorb water in the intestine and swell up. That makes the stool larger and softer, which can encourage the bowel to contract and move it along. They are not usually fast, and they often take a day or two, or sometimes a little longer, to have much effect. A natural way of doing something similar is to eat more fiber-rich food, which also adds bulk to the stool.
The second type of laxative softens the stool. Hard, dry stool can be difficult and painful to pass, so these laxatives help water and fats mix into the stool more easily, making it softer and easier to move through the bowel.
The third type is similar, but instead of mainly softening the inside of the stool, it helps coat the stool and sometimes the lining of the bowel in a slippery layer so that it can slide along more easily. These are lubricant laxatives, and mineral oil is the classic example. They can be effective, but they are not ideal for long-term use because they can interfere with the absorption of some nutrients.
The fourth type pulls water into the bowel, and this is the kind many people encounter before a colonoscopy, which is why this topic came to mind today. These are called osmotic laxatives. They work by osmosis, drawing water into the intestine and colon. That extra water softens the stool, increases the volume inside the bowel, and helps trigger bowel movements. Because they shift so much water into the bowel, it is important to drink enough fluids when taking them.
The fifth type of laxative stimulates the nerves in the intestine, especially in the colon, helping to increase peristalsis. These are stimulant laxatives. They encourage the muscles of the bowel to contract more actively, pushing the stool onward. This can make them very effective, but they are generally not something to rely on for a long time because overuse can irritate the bowel.
There are other types of laxative as well, but these are some of the most common. In simple terms, laxatives work by making the stool bigger, softer, slipperier, wetter, or easier for the bowel to push along. And this is what I learned today.
Sources
https://my.clevelandclinic.org/health/body/7041-digestive-system
https://www.healthdirect.gov.au/laxatives
https://www.nhs.uk/medicines/laxatives
https://en.wikipedia.org/wiki/Laxative
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