Antidiarrheal Medications and When to Use Them

An antidiarrheal is a drug that is used to slow down or stop loose stools (diarrhea). Over-the-counter antidiarrheal medications are found in most drug stores or pharmacies or they can be prescribed by a physician. Antidiarrheals are used for acute, non-life-threatening situations, such as viral gastroenteritis.

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In most cases of diarrhea, taking an antidiarrheal medication will not treat the underlying cause (such as an infection or inflammation), but may help with the discomfort that comes from having repeated watery bowel movements.

For most adults, diarrhea happens a few times a year and goes away on its own. In these cases, antidiarrheal medications probably aren't necessary, especially when the cause of the diarrhea isn't known.

For people who have digestive diseases, such as inflammatory bowel disease (IBD), it might seem like a good idea to take something for diarrhea, but in some cases, it might not work. There is also the possibility that antidiarrheal drugs may be harmful to certain types of IBD.

Check with a doctor about using a drug for diarrhea if it goes on for more than a few days or if it causes dehydration. People with IBD should always ask a doctor before using an antidiarrheal medication.


Diarrhea is a common condition that can have a wide variety of causes. In many cases, diarrhea will go away on its own after a few days, and the cause may never be known.

Do not take antidiarrheal agents when diarrhea is accompanied by fever, severe illness, abdominal pain, or if there is blood or pus (mucus) in the stool. If diarrhea from an infection is a possibility, only use antidiarrheal drugs with the help of a healthcare professional.

Antidiarrheal Drugs

Antidiarrheal drugs are usually not prescribed to treat IBD because this doesn't treat the inflammation that's causing diarrhea.

With ulcerative colitis, in particular, antidiarrheal drugs have been linked to a rare but very serious condition known as toxic megacolon. Toxic megacolon is less common in people who have Crohn's disease.

Antidiarrheals should only be used by people who have IBD under the direction and supervision of a gastroenterologist.

People who have had j-pouch surgery may be advised to use anti-diarrheal medications, especially during recovery from the final surgery (takedown surgery) when the j-pouch is connected.

Some people with j-pouches may use antidiarrheals on a long-term basis, while others might use them only as needed when having too many bowel movements a day for some reason.

Types of Antidiarrheal Drugs

Antidiarrheal medications are made from two main ingredients, loperamide, and bismuth subsalicylate. These medicines work in different ways.

Loperamide (Imodium)

Imodium, which can be purchased over-the-counter, decreases the speed and number of intestinal contractions, which has the effect of slowing down diarrhea.

Side effects of loperamide can include abdominal pain, dry mouth, drowsiness, dizziness, constipation, nausea, and vomiting. People who have these side effects from loperamide may find that they aren't able to drive or do other activities that require concentration while taking it.

If you haven't used loperamide before or aren't used to taking it on a regular basis, avoid driving and operating heavy machinery until you know how it affects you.

Some people with j-pouches use this medication on a regular basis and might get a prescription for it from a physician.

Bismuth Subsalicylate

Bismuth subsalicylate, found in Kaopectate and Pepto-Bismol, is better known for treating stomach upset, but it also works as an antidiarrheal and an anti-inflammatory and it can inhibit the spread of some strains of bacteria that causes diarrhea.

Bismuth subsalicylate works to slow diarrhea by reducing the amount of water entering the bowels. Side effects of Pepto-Bismol include constipation, black stools, or a black tongue. Overdoses of Pepto-Bismol can be dangerous, so only take the prescribed amount and don't double up doses.

A Word From Verywell

Diarrhea that goes on for more than a few days or is accompanied by a fever, severe abdominal pain, blood or pus in the stool is a cause to call a physician right away. Not being able to keep any foods or liquids down is another reason to seek medical attention right away.

In most cases, the virus or bacteria will clear the body in a few days, although it might take several more days to feel back to normal. Diarrhea shouldn't be constant, so if it's going on for a long time, it's time to get checked out by a physician and see if there's something else going on.

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Article Sources
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  1. Merck Manual Professional Version. Diarrhea. Updated May 2018.

  2. Strong SA. Management of acute colitis and toxic megacolon. Clin Colon Rectal Surg. 2010;23(4):274-84. doi:10.1055/s-0030-1268254

  3. Merck Manual Professional Version. Loperamide.

  4. Pepto Bismol. Symptoms.

Additional Reading
  • American Society of Health-System Pharmacists. "Bismuth subsalicylate." U.S. National Library of Medicine.

  • American Society of Health-System Pharmacists. "Loperamide." U.S. National Library of Medicine.