The two most effective over-the-counter medicines for stopping diarrhea are loperamide (sold as Imodium) and bismuth subsalicylate (sold as Pepto-Bismol and Kaopectate). Loperamide works faster and reduces loose stools by about 50%, with noticeable improvement within the first four hours. Bismuth subsalicylate works more gradually and is better suited for milder symptoms or prevention.
Loperamide: The Fastest OTC Option
Loperamide slows down your gut and reduces the amount of fluid your intestines release, which means fewer trips to the bathroom and firmer stools. It starts working within hours, making it the go-to choice when you need quick relief from acute, non-infectious diarrhea.
The FDA-approved maximum for over-the-counter use is 8 mg per day for adults. Most products come in 2 mg tablets or capsules, so that means no more than four in a 24-hour period. The typical approach is to take two tablets after the first loose stool, then one after each subsequent loose stool, staying within that daily cap. Prescription use allows up to 16 mg per day, but only under medical supervision.
One important safety note: at doses above what’s recommended, loperamide can interfere with your heart’s electrical rhythm, potentially causing dangerous or even fatal heart rhythm problems. This risk increases in adolescents, whose livers may not break down the drug as efficiently, allowing a more potent byproduct to build up. Stick to the labeled dose and never take extra thinking it will work better.
Bismuth Subsalicylate: A Gentler Alternative
Bismuth subsalicylate is harder to classify because it does several things at once. It has mild antimicrobial properties, reduces fluid secretion in the gut, and absorbs irritants. It’s slower to kick in than loperamide, but it also soothes nausea and stomach upset, which makes it a solid choice when diarrhea comes with an unsettled stomach.
This is also the medicine used for preventing traveler’s diarrhea. Taken four times daily with meals and at bedtime, it can reduce your risk of getting sick during trips lasting up to two weeks. If you’re already dealing with traveler’s diarrhea, it can shorten the episode, though loperamide will control symptoms faster.
Bismuth subsalicylate contains a compound related to aspirin. Because of this, it’s not routinely recommended for children or teenagers due to the potential risk of Reye syndrome, a rare but serious condition that affects the liver and brain. It can also turn your tongue and stool black temporarily, which is harmless but can be alarming if you’re not expecting it.
When You Should Not Take Antidiarrheals
Not all diarrhea should be stopped with medication. Loperamide is contraindicated if you have bloody stools, a high fever, or diarrhea caused by a bacterial infection. In those situations, diarrhea is your body’s way of flushing out a pathogen, and slowing that process can make things worse. The same applies to active ulcerative colitis flares. Children under 2 should never take loperamide.
If your diarrhea includes blood or looks black and tarry, or if you develop severe abdominal pain, skip the OTC aisle and get medical attention. For adults, diarrhea lasting more than two days without improvement also warrants a visit. For children, the threshold is shorter: 24 hours. Signs of dehydration like excessive thirst, very dark urine, dizziness, dry mouth, or little to no urination are reasons to seek help regardless of how long symptoms have lasted.
Prescription Options for Specific Causes
When diarrhea is caused by an identified infection, a doctor may prescribe targeted treatment rather than a symptom-stopping drug. For traveler’s diarrhea caused by certain strains of E. coli, a gut-specific antibiotic called rifaximin is commonly used. It works almost entirely inside the intestine with very little absorption into the bloodstream, which limits side effects. For parasitic infections like Giardia or Cryptosporidium, a different prescription antiparasitic is typically used.
These aren’t medicines you’d pick up on your own. They require a diagnosis, which is why persistent or severe diarrhea, especially after international travel, calls for a stool test rather than more OTC tablets.
Probiotics Can Shorten Recovery
Probiotics won’t stop diarrhea the way loperamide does, but they can meaningfully reduce how long an episode lasts. The strongest evidence is for a yeast-based probiotic called Saccharomyces boulardii. A large meta-analysis covering over 13,000 children found it shortened diarrhea by about 1.25 days compared to placebo and cut the odds of diarrhea lasting two or more days by nearly 80%. Other strains with good evidence include Lactobacillus reuteri (which shortened episodes by about 0.84 days) and Bifidobacterium lactis.
While much of this research was done in children, Saccharomyces boulardii is widely available for adults and is commonly recommended alongside other treatments. You can find it in most pharmacies, often marketed specifically for digestive support. It’s generally well tolerated and can be taken alongside loperamide or bismuth subsalicylate.
Choosing the Right Approach
Your best option depends on what’s causing the diarrhea and how severe it is. For a straightforward case of acute diarrhea with no fever or blood, loperamide is the fastest and most effective OTC choice. If your symptoms are milder or you also have nausea, bismuth subsalicylate covers more ground. Adding a probiotic like Saccharomyces boulardii can help either way.
While you’re managing symptoms, staying hydrated matters more than any pill. Diarrhea pulls water and electrolytes out of your body quickly. Oral rehydration solutions, broths, and diluted juices help replace what you’re losing. Most episodes of acute diarrhea resolve within a few days on their own, and medication simply makes those days more manageable.