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Pepto Bismol vs Imodium for IBS

If you experience repeating flares of tummy pain, diarrhea, constipation, bloating, and cramping, you might have irritable bowel syndrome (IBS).

IBS patients fit the Rome criteria, which is used by doctors to diagnose the condition.

According to the Rome criteria, you have IBS if you experience abdominal pain at least 1 day per week during a 3-month period. The pain must be associated with a change in bowel habits — either a change in stool frequency or appearance.

There are multiple subtypes of IBS depending on the dominant pattern of bowel habits. These include IBS-D (for diarrhea), IBS-C (constipation), and IBS-M (mixed).

Patients with IBS-D and IBS-M can experience disabling bouts of diarrhea. In this article, we’ll take a look at two drugs for diarrhea — Imodium and Pepto Bismol.

Let’s see how the two differ in terms of their actions, side effects, and effectiveness in treating diarrhea associated with IBS.


What is Pepto Bismol?


Pepto Bismol is the brand name for a drug called bismuth subsalicylate, which is mainly used as an anti-diarrheal drug but can also treat additional symptoms such as heartburn, gas, belching, and indigestion.

These symptoms are common among IBS patients, which is why your doctor may prescribe Pepto Bismol to you if you have IBS-D.

Pepto Bismol works via several mechanisms, which include blocking toxins produced by the diarrhea-causing bug E.coli, increasing intestinal water absorption (which reduces diarrhea volume), reducing gut inflammation associated with diarrhea, and blocking prostaglandin release.

Prostaglandins are a class of chemicals that promote inflammation in the body and increased production can be seen in diarrhea from inflammatory causes.

Bismuth subsalicylate is also sometimes used to treat an H.pylori infection when other treatments fail. H.pylori is a major cause of stomach and small intestine ulcers.

Most bismuth subsalicylate preparations are taken via the mouth and side effects are typically mild and short-lived. Side effects include:
● Black discoloration of stool
● Black tongue
● Ringing ears — this is considered a severe side effect and immediate medical attention must be sought if you experience this after taking Pepto Bismol

Unfortunately, there’s a long list of drugs that can interact with bismuth subsalicylate. This means bismuth can alter their levels in the blood. Reduced drug levels make a drug ineffective while inappropriately high levels can lead to toxicity and severe side effects.

Examples of drugs that can interact with Pepto Bismol include:

● Blood pressure drugs called ACE inhibitors
● The anti-cancer drug methotrexate
● NSAIDs like aspirin and naproxen. These drugs are commonly used and you may have used one to treat a headache.
● Certain antibiotics
● Warfarin, which prevents abnormal blood clotting
● Diabetes drugs

If you’re currently taking any drug, it’s important to consult a doctor before taking Pepto Bismol and confirm that it won’t interact with your current medication.

You should also stay away from bismuth subsalicylate if you are allergic to salicylates, are experiencing black stools prior to starting Pepto Bismol (this could be a sign of gut bleeding or ulcer), or a teenager recovering from a viral infection like chickenpox.


How does Imodium differ from Pepto Bismol?


Just like Pepto Bismol, Imodium is an anti-diarrheal drug. It’s also sometimes prescribed by doctors to treat IBS-D patients. However, Imodium works by a different mechanism, has different side effects, and fewer drug interactions compared to Pepto Bismol.

Imodium is the brand name of loperamide. Unlike Pepto Bismol, Imodium works by binding to opioid receptors in the gut. This triggers a series of chemical reactions, which results in reduced production of a chemical called acetylcholine.

Acetylcholine is responsible for normal, intermittent gut contractions that transmit food from mouth to the anus. In diarrhea, the frequency of these contractions is increased, which impairs gut reabsorption of water. This makes the stool loose and increases its frequency.

When you take loperamide, acetylcholine production is reduced and gut contractions decrease in number. This allows more time for water reabsorption, improving diarrhea.

Since Imodium binds to opiate receptors, it can cause side effects like:
● Headache
● Nausea
● Constipation, which may be a problem if you have IBS-M
● Dry mouth
● Dizziness
● Allergic reaction — this is a rare and serious side effect of Imodium. If you experience difficulty breathing and swelling around the mouth, contact a doctor immediately.

Just like Pepto Bismol, Imodium can interact with a variety of drugs although the list is relatively smaller. These include:

● The diabetes drug pramlintide
● Anticholinergic drugs
● Some antihistamines
● HIV drugs

It’s also important to know that you’re not supposed to use Imodium for more than two days until advised by a doctor, which is a major factor that limits its effectiveness in IBS.


Do Pepto Bismol and Imodium work for IBS-D?


Yes, Pepto Bismol and Imodium (as well as other over-the-counter antidiarrheals) are prescribed by doctors to treat the diarrhea associated with IBS-D.

However, it’s important to realize that diarrhea is only one component of IBS, which is a complex gut disorder with many other symptoms.

Research has shown that OTC antidiarrheals like Imodium treat diarrhea associated with IBS but not other gut symptoms that the condition causes.

Plus, while Pepto Bismol and Imodium may treat your current bout of diarrhea, the chronic nature of IBS means that another episode is very likely and these drugs do nothing to minimize its risk. Antidiarrheals only treat a symptom of IBS and do nothing to ease the underlying abnormal processes that cause the condition.

Nonetheless, you should be aware that limited research has been conducted to study the long-term use and effectiveness of bismuth (found in Pepto Bismol) for persistent diarrhea caused by IBS. 2 out of 4 IBS-D patients in a study showed sustained response to bismuth. This sample size is too small to draw any meaningful conclusion from the study, so doctors currently don’t use OTC antidiarrheals for long-term treatment of IBS. Instead, a holistic approach is used, which includes treatments like:

● Diet modification (which includes avoiding trigger foods and trying out a low-FODMAP diet)
● Stress management
● Probiotic supplements — products containing Bifidobacterium may be useful in IBS
● Medical drugs

It’s best to approach IBS holistically instead of completely relying on OTC antidiarrheals like Pepto Bismol and Imodium.

Medically reviewed by Onikepe Adegbola, MD PhD


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