Loperamide (sold as Imodium) is the most effective over-the-counter medicine for stopping diarrhea quickly in adults. It slows gut motility, giving your intestines more time to absorb water, and it works faster than other OTC options. But the “best” choice depends on what’s causing your diarrhea, how severe it is, and whether you’re treating an adult or a child. In some cases, the smartest move is skipping anti-diarrheal medicine entirely and focusing on fluids.
Loperamide: The Fastest OTC Option
Loperamide is the go-to for acute diarrhea in adults and teens 13 and older. The standard approach is to take two capsules (4 mg total) after your first loose bowel movement, then one capsule (2 mg) after each subsequent loose stool. The maximum for over-the-counter use is 8 mg (four tablets) in 24 hours. If a doctor is managing your treatment for chronic diarrhea, they may allow up to 16 mg per day.
Loperamide works by slowing the muscles in your intestinal wall. This means food and fluid spend more time in your gut, so your body absorbs more water and your stools firm up. For a straightforward case of stomach flu or food-related diarrhea, it provides noticeable relief within an hour or two.
The trade-off is that loperamide can cause constipation once the diarrhea resolves, and it’s not safe in every situation. More on that below.
Bismuth Subsalicylate: A Gentler Alternative
Bismuth subsalicylate (the active ingredient in Pepto-Bismol and Kaopectate) takes a different approach. Rather than slowing your gut, it reduces inflammation in the intestinal lining and has mild antibacterial properties. It also helps with the nausea and cramping that often come alongside diarrhea, making it a better fit when your stomach feels unsettled overall.
It won’t stop diarrhea as quickly as loperamide, but it’s a reasonable choice for mild cases or when you want symptom relief without completely halting bowel movements. It’s also commonly recommended for preventing traveler’s diarrhea. Be aware that it can temporarily turn your tongue and stools black, which is harmless but surprising if you’re not expecting it. Because it contains a compound related to aspirin, anyone with an aspirin allergy or who takes blood thinners should avoid it.
Probiotics: Helpful but Not a Quick Fix
Probiotics won’t stop diarrhea the way loperamide does, but specific strains can shorten how long an episode lasts. A large meta-analysis of randomized controlled trials found that Saccharomyces boulardii, a beneficial yeast, reduced diarrhea duration by about 1.25 days compared to placebo and cut the risk of diarrhea lasting two or more days by roughly 78%. It performed better than other probiotic strains tested, including Lactobacillus rhamnosus GG, which showed less consistent results in placebo-controlled trials.
Probiotics make the most sense as a complement to other treatment, not a replacement. If you’re dealing with antibiotic-associated diarrhea or recovering from a stomach bug and want to restore your gut balance, Saccharomyces boulardii has the strongest evidence behind it. Look for it by name on the label.
Racecadotril: A Newer Option in Some Countries
Racecadotril works differently from loperamide. Instead of slowing your gut, it blocks excess fluid secretion into the intestines while leaving normal gut movement intact. In six randomized studies comparing the two, racecadotril resolved diarrhea at a similar speed to loperamide, and one study in older adults found it worked better.
The real advantage is side effects. Patients taking racecadotril were about 66% less likely to develop rebound constipation compared to those on loperamide, and overall adverse events were consistently lower. It’s widely available in Europe and parts of Asia and Latin America but is not currently sold over the counter in the United States. If you’re traveling and see it in a pharmacy abroad, it’s a well-studied alternative worth knowing about.
When Medicine Can Make Things Worse
Anti-diarrheal medications like loperamide should not be used if you have bloody stools, a fever above 101.3°F (38.5°C), or suspect a bacterial infection. In infections caused by bacteria like Salmonella, Shigella, Campylobacter, or C. difficile, slowing your gut with loperamide can trap the pathogen inside, potentially making the infection more severe. Diarrhea in these cases is your body’s way of flushing out something harmful, and blocking that process can backfire.
If your diarrhea came on after a course of antibiotics, be especially cautious. Antibiotic-associated diarrhea can sometimes signal a C. difficile infection, where antimotility drugs are specifically dangerous. In these situations, rehydration is the priority while the underlying cause is addressed.
Children Need a Different Approach
Antidiarrheal medications, including both loperamide and bismuth subsalicylate, are not recommended for infants or young children. The risks outweigh the benefits. Loperamide can worsen certain types of diarrhea in kids, and bismuth subsalicylate carries a risk related to Reye’s syndrome, similar to aspirin in children.
For children, the focus should be entirely on preventing dehydration. Oral rehydration solutions are the standard treatment worldwide. The WHO-recommended formula contains a precise balance of sodium (75 mmol/L), glucose (75 mmol/L), and potassium (20 mmol/L) at a total concentration of 245 mOsm/L. Pre-mixed versions are available at most pharmacies under brands like Pedialyte. Small, frequent sips work better than large amounts at once, especially if the child is also vomiting.
Hydration Matters More Than Medication
Regardless of which medicine you choose, replacing lost fluids is the most important part of treating diarrhea. Most acute episodes resolve on their own within one to two days. Medicine manages the symptoms, but dehydration is what actually makes you feel terrible and, in severe cases, what sends people to the emergency room.
Water alone isn’t ideal because diarrhea drains electrolytes, particularly sodium and potassium. Oral rehydration solutions are the gold standard, but if you don’t have one on hand, broth, diluted juice, or sports drinks can help bridge the gap. Signs that dehydration is becoming a problem include dark urine, dizziness when standing, a dry mouth, and producing very little urine. In adults, diarrhea lasting more than two days without improvement, or any episode involving high fever or bloody stools, warrants medical evaluation.
Traveler’s Diarrhea: When You May Need Antibiotics
Traveler’s diarrhea follows a severity-based treatment approach. Mild cases that don’t interfere with your plans can be managed with loperamide or bismuth subsalicylate alone. Moderate diarrhea that disrupts your activities may warrant antibiotics. Severe or incapacitating diarrhea, and any case involving bloody stools, calls for antibiotic treatment.
The CDC considers azithromycin the preferred antibiotic, particularly for travel in Southeast Asia where antibiotic-resistant bacteria are common, and for any case involving fever or bloody diarrhea. Fluoroquinolones are another option for non-invasive cases. Combining an antibiotic with loperamide is a common strategy that addresses both the infection and the symptoms simultaneously, though loperamide should not be used alone when bloody stools or fever are present.
If you’re planning travel to a region where traveler’s diarrhea is likely, talking to your doctor beforehand about carrying a prescription antibiotic is practical. Having the right medication in your bag can mean the difference between losing one day of a trip and losing several.