Loperamide (sold as Imodium A-D) is the most effective over-the-counter medicine for stopping diarrhea quickly. In head-to-head comparisons with bismuth subsalicylate (Pepto-Bismol), loperamide significantly reduced the number of unformed bowel movements, controlled symptoms for longer after the first dose, and was rated better by patients for overall relief within 24 hours. That said, it’s not always the right choice. The best OTC option for you depends on what’s causing your diarrhea, how severe it is, and whether you have certain symptoms that call for a different approach.
How Loperamide Works
Loperamide slows the movement of your intestines, giving your body more time to absorb water from stool. This means fewer trips to the bathroom and firmer stools. It works fast, often providing noticeable relief within an hour of the first dose.
The maximum OTC dose for adults is 8 mg per day, which translates to four caplets or tablets in a 24-hour period (most products contain 2 mg per dose). You take two caplets after your first loose stool, then one after each subsequent loose stool, stopping at that daily cap. If your diarrhea hasn’t improved after two days, it’s time to talk to a doctor rather than keep taking it.
How Bismuth Subsalicylate Works
Bismuth subsalicylate, the active ingredient in Pepto-Bismol and Kaopectate, takes a fundamentally different approach. When you swallow it, it breaks down into two components in your stomach. One reduces inflammation and slows the overproduction of fluid in your intestines by blocking the same chemical pathway that ibuprofen targets. The other has direct antibacterial properties, preventing bacteria from latching onto the lining of your gut.
This dual action makes bismuth subsalicylate particularly useful when your diarrhea is caused by a bacterial source, like food poisoning or traveler’s diarrhea. It won’t stop symptoms as quickly as loperamide, but it actively fights the bugs causing the problem rather than simply slowing your gut down. The CDC lists both loperamide and bismuth subsalicylate as options for mild traveler’s diarrhea, and some travelers use them together.
One cosmetic side effect worth knowing: bismuth subsalicylate can temporarily turn your tongue and stool black. This is harmless and goes away after you stop taking it.
When to Use Which
For garden-variety diarrhea from a stomach bug, a stressful day, or something you ate, loperamide is the faster, more effective choice. It’s especially practical when you need to get through a work meeting, a flight, or any situation where frequent bathroom access isn’t an option.
Bismuth subsalicylate is the better pick when your diarrhea comes with nausea, heartburn, or an upset stomach, since it treats all of those symptoms at once. It’s also a reasonable first choice when you suspect a mild bacterial cause, like the early stages of traveler’s diarrhea, because its antimicrobial properties address the infection itself.
For moderate to severe traveler’s diarrhea, meaning symptoms that interfere with your plans or include bloody stool, the CDC recommends antibiotics rather than relying on OTC options alone. Loperamide can still be used alongside antibiotics for symptom relief in those cases.
What About Probiotics?
Probiotics are widely marketed for digestive health, but the evidence for treating active diarrhea is disappointing. A large Cochrane review analyzing data from thousands of participants found that probiotics probably make little or no difference in how long diarrhea lasts or how many people still have symptoms after 48 hours. This held true even for the most commonly recommended strains. Probiotics may support general gut health over time, but they’re not a reliable treatment when you need diarrhea to stop now.
When OTC Medicine Isn’t Safe
Loperamide works by keeping things in your gut longer. That’s great for a routine stomach bug, but dangerous when your body is trying to flush out certain harmful bacteria. You should avoid loperamide if you have bloody or black stools, a fever over 102°F, or any reason to suspect a serious bacterial infection. Conditions caused by specific dangerous bacteria, including C. difficile infection and E. coli O157:H7, can worsen significantly with anti-motility drugs. There are case reports of toxic megacolon, a life-threatening complication, linked to loperamide use during serious intestinal infections.
For adults, diarrhea that lasts more than two days without improvement, signs of dehydration (excessive thirst, dark urine, dizziness, very little urination), severe abdominal pain, or a high fever all warrant medical attention rather than continued OTC treatment. More than 10 bowel movements a day, or fluid losses that outpace what you can drink, also cross the line into territory that needs professional care.
Children Need a Different Approach
OTC diarrhea medicines are not interchangeable between adults and children. Loperamide should not be given to children under 2 at all, and even in older children who are malnourished, dehydrated, or have bloody stool, the risks outweigh the benefits. Bismuth subsalicylate contains a salicylate compound, which is chemically related to aspirin and carries a risk of Reye’s syndrome in children with viral illnesses.
For kids, the priority is preventing dehydration with oral rehydration solutions rather than stopping the diarrhea itself. If a child’s diarrhea hasn’t improved within 24 hours, or you notice signs like no wet diapers for three or more hours, a sunken appearance around the eyes or belly, crying without tears, or unusual drowsiness, those are signals to get medical help promptly.
Pregnancy and Breastfeeding
Bismuth subsalicylate is generally not recommended during pregnancy because its salicylate component poses risks similar to aspirin, particularly in the third trimester. Loperamide is the safer OTC option for pregnant individuals, though it’s still worth discussing with your provider if symptoms are persistent.
For breastfeeding, research on a closely related compound shows that only minimal amounts of loperamide make it into breast milk. Standard doses are unlikely to affect a nursing infant. Bismuth subsalicylate, however, remains a concern during breastfeeding due to its salicylate content.
Staying Hydrated Matters More Than Medication
No matter which OTC medicine you reach for, replacing lost fluids is the single most important thing you can do during a bout of diarrhea. Water alone is fine for mild cases, but if diarrhea is frequent or lasting more than a day, drinks with electrolytes (sodium, potassium, and a small amount of sugar) help your body absorb fluid more efficiently. Broth, diluted juice, or commercial oral rehydration solutions all work. Avoid caffeine and alcohol, which can make dehydration worse.