Two over-the-counter medicines are widely used to stop diarrhea: loperamide (sold as Imodium) and bismuth subsalicylate (sold as Pepto-Bismol and Kaopectate). Loperamide is the stronger option and works by slowing movement through your intestines, giving your body more time to absorb water from stool. Bismuth subsalicylate takes a gentler approach, reducing inflammation and excess fluid in the gut while also helping with nausea and stomach upset. Which one you should reach for depends on your symptoms, your age, and what’s causing the diarrhea in the first place.
Loperamide: The Fastest Option
Loperamide is the go-to for stopping acute diarrhea quickly. It works by slowing the muscular contractions in your intestines, which means food and fluid spend more time being absorbed instead of rushing through. Most people notice a significant reduction in trips to the bathroom within an hour or two of their first dose.
The FDA-approved maximum for adults is 8 mg per day when you’re buying it over the counter, and 16 mg per day if a doctor prescribes it at a higher dose. A standard OTC capsule is 2 mg. The typical approach is to take two capsules after your first loose stool, then one capsule after each subsequent loose stool, staying within that 8 mg daily cap. Most bouts of acute diarrhea don’t require more than a day or two of use.
Loperamide interacts with a large number of other medications (over 370 known interactions), so if you take prescription drugs regularly, it’s worth checking with a pharmacist before using it. People with liver or kidney problems should be especially cautious, as the drug is processed through those organs.
Bismuth Subsalicylate: A Milder Alternative
Bismuth subsalicylate is less potent at stopping diarrhea than loperamide, but it pulls double duty. It calms an upset stomach, reduces nausea, and has mild antimicrobial properties that make it particularly useful for traveler’s diarrhea. If your diarrhea comes with cramping and queasiness, this may be the better first choice.
Because bismuth subsalicylate is chemically related to aspirin, certain people need to avoid it entirely. Children under 12 should not take it due to the risk of Reye’s syndrome, a rare but serious condition linked to salicylate products in kids who have or are recovering from a viral illness like the flu or chickenpox. If you’re allergic to aspirin, or you already take another salicylate-containing medication, skip this one. It stays in your system longer than loperamide, with a half-life of about 33 hours, so the effects of any interaction or side effect also linger longer.
A common and harmless side effect: it can temporarily turn your tongue and stool black. This looks alarming but is completely normal and goes away after you stop taking it.
When You Should Not Take Anti-Diarrheal Medicine
Diarrhea is sometimes your body’s way of flushing out a dangerous infection, and stopping that process with medication can make things worse. Loperamide in particular is contraindicated in several situations where slowing the gut could trap harmful bacteria inside.
Do not use loperamide if you have:
- Blood in your stool or a fever above 101°F (38.3°C). These signs point to a bacterial infection where your body needs to expel the pathogen. Trapping bacteria like Salmonella, Shigella, or Campylobacter in the gut can lead to serious complications.
- Diarrhea that started after taking antibiotics. This could signal a C. difficile infection, which produces toxins in the colon. Slowing gut motility keeps those toxins in contact with your intestinal lining longer, raising the risk of a dangerous complication called toxic megacolon.
- Mucus in your stool along with severe abdominal pain. These symptoms suggest something more than a simple stomach bug and need a proper evaluation before you treat them at home.
If you start taking loperamide and develop constipation, bloating, or your abdomen feels noticeably distended, stop taking it right away. These can be early signs of ileus, where the intestine stops moving altogether.
Safety for Children
The rules are stricter for kids. Loperamide is FDA-approved only for children over 2 years old, and even then, serious side effects have been reported in children under 3, including those who are malnourished or dehydrated. In young children, the risks of loperamide often outweigh the benefits, even at very low doses. For most kids with acute diarrhea, the priority should be replacing lost fluids with an oral rehydration solution rather than stopping the diarrhea itself.
Bismuth subsalicylate should not be used in children under 12 because of the Reye’s syndrome risk. This essentially means most young children should not be given either major OTC anti-diarrheal without specific guidance from their pediatrician.
Probiotics Can Shorten Recovery
Probiotics won’t stop diarrhea as abruptly as loperamide, but they can meaningfully cut its duration. A large Cochrane review found that probiotics reduced the average length of infectious diarrhea by about 30 hours compared to no treatment. They also reduced the chance of diarrhea lasting three or more days by roughly a third.
The yeast strain Saccharomyces boulardii has some of the strongest evidence. In one study, people taking it were 59% less likely to still have diarrhea by day four. Lactobacillus-based probiotics, particularly the strain commonly labeled LGG, also showed significant benefits, especially in children with rotavirus, where diarrhea duration dropped by an average of 38 hours. You can find these strains in supplements at most pharmacies. They’re safe to take alongside OTC anti-diarrheals.
Prescription Options for Chronic Diarrhea
If your diarrhea has been going on for weeks rather than days, OTC medicines may mask the symptom without addressing the cause. Chronic diarrhea often has an identifiable and treatable trigger, and the prescription your doctor chooses will depend on what that trigger is.
For diarrhea caused by irritable bowel syndrome (IBS-D), there are targeted medications that calm the overactive nerve signals in the gut. If the problem traces back to excess bile acids reaching the colon, which happens in some people after gallbladder removal or due to other digestive changes, bile acid binders can absorb the irritating bile before it causes loose stools. Diabetes-related diarrhea, caused by nerve damage affecting the gut, has its own class of treatments. And of course, if an underlying infection is driving chronic symptoms, the right antibiotic or antiparasitic resolves the problem at its source.
Hydration Matters More Than Medication
Regardless of which medicine you take, the biggest risk from diarrhea isn’t the diarrhea itself. It’s dehydration. Every loose stool pulls water and electrolytes out of your body, and if you’re not replacing them, you can end up dizzy, fatigued, and in serious trouble faster than you’d expect. This is especially true for young children and older adults.
Drink water, broth, or an oral rehydration solution throughout the day. Sports drinks work in a pinch but contain more sugar and less sodium than ideal. If your urine is dark yellow or you’re producing very little of it, you’re already behind on fluids. Anti-diarrheal medicine handles the symptom, but staying hydrated is what keeps a bad day from becoming a medical emergency.