Antidiarrheal Medications and When to Use Them

An antidiarrheal is a drug that is used to slow down or stop diarrhea (loose stools). Over-the-counter antidiarrheal medications are found in most drug stores or pharmacies, and some anti-diarrhea medications are available only by prescription. Antidiarrheals are used for acute, non-life-threatening situations, such as viral gastroenteritis.

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 watery bowel movements.

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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 your 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 as advised by a healthcare professional.

Antidiarrheal Drugs

Antidiarrheal drugs are usually not prescribed to treat IBD because this type of medication 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, such as when having too many bowel movements a day.

Types of Antidiarrheal Drugs

Antidiarrheal medications are made from two main ingredients, loperamide, and bismuth subsalicylate, and they work in different ways. There are prescription medications that are sometimes used for treating chronic diarrhea, and you can discuss with your doctor if those are appropriate for you.

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 be unable to drive or do other activities that require concentration while taking it. Also, if you have a history of heart rhythm problems, you should talk to your doctor before using loperamide.

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 is common, and 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. If it continues for a long time, it's time to get checked out by a physician and see if there's something else going on.

Diarrhea that lasts 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.

Frequently Asked Questions

  • Is antidiarrheal medicine available over the counter?

    Yes, various antidiarrheal medication options are available over the counter at pharmacies and many grocery stores. Pepto-Bismol and Kaopectate and their generic equivalents are two common products. Alternatively you can try Imodium, which slows intestinal contractions and reduces bouts of diarrhea.

  • Can Imodium cause constipation?

    Yes, constipation is one side effect of Imodium. Other potential side effects include dizziness, drowsiness, headache, nausea, and vomiting. Most people don't experience side effects from taking Imodium, but if you take other medications, talk to your doctor or pharmacist first to see if there's a potential for medicine interactions.

  • How long does it take Imodium to wear off?

    A single dose of Imodium can last for 8 to 12 hours. It takes about half an hour for the medicine to begin working.

6 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.
  1. Merck Manual Professional Version. Diarrhea.

  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.

  5. National Health Service (NHS). Loperamide.

  6. National Health Service (NHS). How to take Loperamide (Imodium).

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.

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.