How Laxatives Treat Constipation

While all laxatives aim to induce a bowel movement by softening the stool, they achieve this goal in different ways. How a laxative works will depend on the type of laxative it is and how it's designed. For example, some laxatives make it harder for water to be withdrawn from the stool while others add water to the stool to soften it.

This article will explain more about what laxatives are, the different type of laxatives and how they work, and any side effects.

Psyllium Pills
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What's a Laxative?

A laxative is any type of food, medication, or supplement that will cause a person to have a bowel movement. Laxatives vary widely in how fast they work. Laxatives that are prescribed for use before a colonoscopy, for example, are going to work quicker and with more vigor than ones that are used for a case of mild, infrequent constipation.

Laxatives come in the following form:

  • Liquid
  • Pills
  • Powders that can be mixed into liquid
  • Suppositories, which are dissolvable capsules that are inserted into the anus
  • Enemas, or liquid that can be squeezed from a tube into the anus

Laxatives are generally used or prescribed to treat constipation that is not responding to other treatments, such as eating high-fiber foods or drinking more liquids.

The use of laxatives on a regular basis (except bulk-forming laxatives) is typically not recommended, except in certain circumstances and on the advice of a healthcare provider. A healthcare provider will be able to make the determination as to which laxative will be most effective in each particular case.

How Do Laxatives Work?

Many types of laxatives are available over-the-counter in drug stores, though you may need a prescription for long-term constipation. Although all laxatives are designed to bring on a bowel movement, the underlying mechanism will depend on which type you use.

Bulk-Forming Laxatives

This type of laxative, which includes such brand names as FiberCon, Metamucil, and Citrucel, is made of a type of fiber that is not absorbed by the intestine. Because the fiber in these supplements is not absorbed by the intestines, they pass all the way through the digestive tract.

This type of fiber absorbs water and softens the stool, which makes having a bowel movement easier. Bulk-forming laxatives can be safely used long-term and are effective for treating both diarrhea and constipation. It can take between 12 hours to several days for bulk-forming laxatives to induce a bowel movement.

Benefiber, a more soluble fiber, tends to cause less bloating and extension.

Emollient Laxatives

Emollients are a type of laxative also known as a stool softener. This type of medication works by helping the body pull more fat and water into the stool, which helps make the stool softer and easier to pass. You'll typically see results between 12 hours and three days with these laxatives.

Lubricant Laxatives

Lubricants are oily and they work by coating the stool, making it difficult for water to be withdrawn. The stool holds on to more water, and this extra water helps to keep it soft and it is easier to pass as a bowel movement. Lubricant laxatives can work quickly, bringing on a bowel movement within six to eight hours. Mineral oil is one example of a lubricant laxative.

Hyperosmotic Laxatives

This type of laxative includes milk of magnesia or Epsom salts. They aid in easing constipation by causing more water to be drawn into the intestine. The extra water keeps the stool soft, avoiding constipation and making it easier to pass.

They typically begin working after two or three days.

Stimulant Laxatives

Stimulants, such as castor oil, work by speeding up the movement of the muscles in the intestines to pass the waste material through. This movement, which is the muscles contracting in order to propel food on its way through the digestive tract, is called peristalsis. When peristalsis is sped up, stool is passed through the body at a faster than normal rate, which helps to prevent it from becoming thicker and causing constipation. Bowel movements usually come on between six and 12 hours later.

Natural Laxatives

Some foods that tend to have mild laxative properties, such as prunes and prune juice. Figs, licorice, and rhubarb may also help relieve constipation along with other foods that are high in fiber.

The high fiber content tends to act like a bulk-forming laxative, helping to soften the stool. Eating typical serving sizes of foods that are natural laxatives won't have a harsh effect on the body or harm to the intestines.

Rectal Laxatives

Rectal laxatives are suppositories and enemas, which induce a bowel movement faster than other methods. They may take between 15 minutes and an hour to work. They come in a variety of types, including hyperosmotic, lubricant, stimulants, and emollients.

Bowel Prep Laxatives

Laxatives may also be given to clean the bowel in preparation for a test, such as a colonoscopy, or before surgery. These types of laxatives are typically used under the care of a physician. They may include any of the above listed medical laxatives and sometimes more than one form.

Side Effects of Taking Laxatives

Following the directions on the medication label can minimize side effects. Aside from bringing on a bowel movement, laxatives may cause:

  • Bloating
  • Gassiness
  • Abdominal pain

For most healthy people, taking a laxative should be a rare occurrence. People who take laxatives for longer than recommended or in higher doses can become physically and psychologically dependent on them, leading to something called laxative abuse. This can weaken the muscles of the intestines, making it harder to have a bowel movement.

When Should I Contact a Healthcare Provider?

It's best to contact a healthcare provider if you're constipated and unsure about which laxative to try. You should also contact a healthcare provider before taking a laxative if you're:

  • Pregnant
  • Breastfeeding
  • Taking prescription medication

Talk to a medical professional before taking a laxative for more than a week or if the laxative doesn't seem to be working. Seek immediate medical care if you're bleeding from your rectum.

Summary

Laxatives are used to treat constipation or to flush stool from the colon before a medical procedure, such as a colonoscopy. There are many types that work to induce a bowel movement in different ways: Stool softeners pull fat and water into the stool to soften it, for example, while stimulants cause muscles to contract to make stool easier to pass through the intestines. Always follow the label instructions when taking laxatives to prevent side effects and dependence.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.