Loperamide (sold as Imodium) is the most effective over-the-counter medicine for stopping diarrhea in adults. It works by slowing down intestinal movements, which gives your body more time to absorb water and firm up stools. Bismuth subsalicylate (Pepto-Bismol) is another widely available option that can ease milder cases. Which one you should reach for depends on the type of diarrhea, how long it’s lasted, and a few safety considerations worth knowing about.
Loperamide: The Strongest OTC Option
Loperamide is the go-to for acute diarrhea that’s disrupting your day. The standard approach is to take two capsules or tablets (4 mg total) after your first loose bowel movement, then one capsule or tablet (2 mg) after each subsequent loose stool. For over-the-counter use, the maximum is 8 mg (4 tablets) in 24 hours. Prescription use allows up to 16 mg per day for chronic conditions, but you shouldn’t exceed the OTC limit on your own.
Loperamide is safe at recommended doses, but the FDA has issued repeated warnings about serious heart problems, including fatal heart rhythm disturbances, when people take far more than directed. Stick to the label. If you notice a rapid or irregular heartbeat, fainting, or dizziness after taking it, that’s a medical emergency.
One important rule: don’t use loperamide if you have a fever, blood in your stool, or suspect a bacterial infection. In those situations, slowing your gut down can actually trap the pathogen inside and make things worse. Diarrhea caused by infection is your body’s way of flushing out the problem, and blocking that process can be counterproductive.
Bismuth Subsalicylate: A Gentler Alternative
Bismuth subsalicylate, the active ingredient in Pepto-Bismol and Kaopectate, is better suited for milder diarrhea, especially when it comes with nausea or an upset stomach. The typical adult dose is 2 tablets every 30 minutes to an hour as needed, up to 16 tablets in 24 hours. It won’t stop diarrhea as decisively as loperamide, but it can reduce the frequency and discomfort.
This one comes with a specific safety concern for younger people. Bismuth subsalicylate contains a compound related to aspirin, which raises the risk of Reye’s syndrome in children and teenagers recovering from viral infections like the flu or chickenpox. Don’t give it to anyone under 18 who has or is recovering from a viral illness. It can also temporarily turn your tongue and stool black, which looks alarming but is harmless.
Oral Rehydration: The Most Important Step
No matter which medicine you take, replacing lost fluids is the single most important thing you can do during a bout of diarrhea. Dehydration is the real danger, not the diarrhea itself. Signs you’re becoming dehydrated include dark-colored urine, producing very little urine, dizziness, weakness, and fatigue.
Water alone isn’t ideal because diarrhea also drains electrolytes like sodium and potassium. Oral rehydration solutions (available at any pharmacy) replace both water and electrolytes in the right proportions. Broth, diluted juice, and sports drinks can also help, though sports drinks contain more sugar than is ideal. For infants and young children, a pediatric rehydration solution is the best choice. A child who hasn’t had a wet diaper in three or more hours, or who has a dry mouth and tongue, needs fluids urgently.
Probiotics for Prevention and Recovery
Probiotics won’t stop diarrhea the way loperamide does, but they can shorten its duration and reduce the risk of getting it in the first place. A large meta-analysis found that probiotics cut the risk of antibiotic-associated diarrhea by 52% and reduced acute diarrhea from various causes by 34%. The effect was even stronger in children, with a 57% risk reduction compared to 26% in adults.
Several well-studied strains showed similar benefits, including Saccharomyces boulardii (a yeast-based probiotic) and Lactobacillus rhamnosus GG. You can find both in supplement form at most pharmacies. If you’re taking antibiotics and worried about diarrhea as a side effect, starting a probiotic alongside your antibiotic course is a reasonable strategy.
Prescription Medicines for Specific Causes
Most diarrhea clears up on its own or with OTC treatment. But certain types require prescription medication. Traveler’s diarrhea caused by E. coli, for instance, can be treated with a short antibiotic course, typically three days. Irritable bowel syndrome with diarrhea (IBS-D) has its own prescription options that work differently from standard anti-diarrheal drugs, targeting gut bacteria and nerve signaling in the intestine over a two-week treatment period.
Prescription treatment becomes necessary when diarrhea is caused by a specific bacterial, viral, or parasitic infection that your body can’t clear on its own. Your doctor will usually request a stool sample to identify the cause before prescribing anything. Antibiotics are only helpful for bacterial causes and can actually worsen diarrhea caused by certain infections, so getting the right diagnosis matters.
Warning Signs That Need Medical Attention
Most diarrhea resolves within a day or two. If yours persists beyond two days, it’s time to see a doctor. Seek care sooner if you notice blood or black color in your stool, severe abdominal or rectal pain, or a fever above 101°F (38.3°C). These can signal an infection or condition that OTC medicines won’t fix and may actually mask.
For children, the timeline is shorter. A child whose diarrhea hasn’t improved within 24 hours, who has a fever above 102°F, or who shows signs of dehydration needs medical evaluation. Infants and young children dehydrate faster than adults, and what looks like a mild illness can escalate quickly.