Can stool softeners prevent constipation?

Q: After my knee replacement surgery, my surgeon recommended I take a stool softener for a couple of weeks to prevent constipation from my pain medicine. How does that work?

Many surgeons advise their patients to take a stool softener while taking pain medication during the first couple of weeks after surgery. They hope taking a stool softener will help you avoid the discomfort of constipation. This practice has been called into question because very little evidence proves it works. 

The word laxative means “to loosen," similar to the word “relax” and "lax," which means to act loose or relaxed. A laxative works to “loosen” your bowels, relieving constipation. By encouraging the movement of stool through your intestines, a laxative can prevent or reduce the pain and pressure of constipation.

Stool softeners make your stool softer or "slippery," which makes defecation more comfortable but doesn’t prevent or relieve constipation.

After you swallow it, food moves through your digestive tract, a series of tubes. In your stomach, gastric juices mix into your chewed food, which starts the process of digestion. From there, it moves as a liquid mass into your small intestine, where the absorption of vital nutrients begins.

Muscles running the length of your intestines start squeezing in a rhythm, which keeps the mass of food moving from one end to the other. To assist digestion and absorption, your intestines are lined with special cells designed to carry nutrients, medicines, and water out of your intestines into your bloodstream. What’s left behind eventually becomes feces.

The longer food stays in your intestine, the more water can be pulled out of your stool. With less water, your feces becomes smaller, harder, and more painful to eliminate.

A stool softener can draw moisture back into or lubricate the food mass to ease the discomfort of constipation. Two common stool softeners are docusate and mineral oil. 

Docusate is a surfactant, much like detergent or soap. It encourages water to move into your stool. Docusate can replace some of the water your body absorbs as the stool moves through your intestine. It may occasionally cause diarrhea or stomach cramps. Unlike mineral oil, docusate doesn't interfere with the absorption of nutrients or vitamins.

Mineral oil is a liquid refined from crude oil. Unlike docusate, it lubricates the stool instead of increasing its water content. Mineral oil is colorless and odorless. The product “baby oil” is a scented version of mineral oil.

Used over a long period, mineral oil can interfere with your body’s absorption of fat-soluble vitamins like vitamins A, D, E, and K. This can eventually cause a type of vitamin deficiency. Mineral oil can also cause leakage of stool from the rectum.

Accidentally inhaling mineral oil when swallowing can cause life-threatening lung irritation. Mineral oil usually stays in your intestine. However, if you take docusate and mineral oil together, mineral oil can move into your body, away from where you need it to work.

Docusate and mineral oil are called emollients. They turn stool "mushy" but don’t directly stimulate the muscles lining your intestine. (“Mush instead of Push”). Most people notice results within 2 days, but the full effect can take up to five days.

Here are 6 Tips on Using a Stool Softener Effectively:

1.           Stay hydrated.

Drinking enough fluids will help docusate do its job of moving water into your stool.

2.           Avoid docusate sodium if you are on a sodium-restricted diet.

Docusate has two forms, docusate sodium, and docusate calcium. If you restrict your sodium intake, choose docusate calcium instead of docusate sodium. Docusate calcium can be hard to find, so ask a pharmacist for assistance if you don't see it on the shelf.

3.           If you have trouble swallowing pills, avoid 250mg docusate capsules.

The 250g and 100mg capsules are the same prices. I recommend buying the smaller 100mg capsules because the 250mg docusate capsules are HUGE and should never be cut.

4.           Never cut or bite docusate capsules.

Docusate tastes HORRIBLE because it is a soap! Avoid biting or cutting docusate capsules unless you prefer a nasty, soapy flavor that lingers for hours. Docusate liquid and syrup taste nearly as bad. At liquid taste tests I’ve hosted, they rank consistently at the very bottom.

5.           Choose a laxative for constipation prevention or symptoms.

There is little evidence that docusate can prevent constipation. Using a non-prescription laxative like Senakot® and Dulcolax® is much more effective. Docusate is also available in combination with a laxative like senna or bisacodyl. Look for Senakot-S® and Peri-Colace®.

Dr. Louise Achey, Doctor of Pharmacy, is a 43-year veteran of pharmacology and author of Why Dogs Can’t Eat Chocolate: How Medicines Work and How YOU Can Take Them Safely. Get clear answers to your medication questions at her website and blog, TheMedicationInsider.com.

Ó2023 Louise Achey