The two most effective over-the-counter medications for diarrhea are loperamide (sold as Imodium) and bismuth subsalicylate (sold as Pepto-Bismol). Loperamide is the stronger option, working by slowing down intestinal movement so your body has more time to absorb water. Bismuth subsalicylate takes a gentler approach, reducing fluid flow into the bowel and calming inflammation. Which one you should reach for depends on how severe your symptoms are, what’s causing them, and whether certain warning signs are present.
Loperamide: The Most Common Choice
Loperamide is the go-to for stopping loose stools quickly. It slows the muscular contractions of your intestines, giving your gut more time to pull water back out of stool before it passes. For adults, the standard approach is to take two tablets (4 mg) after your first loose bowel movement, then one tablet (2 mg) after each additional loose stool. The FDA-approved maximum is 8 mg per day when you’re using it without a prescription, or 16 mg per day if a doctor is supervising your use.
Sticking to the recommended dose matters more than you might think. The FDA has issued warnings about serious heart rhythm problems linked to high doses of loperamide. At normal doses, it’s safe and effective for most adults. But it’s not appropriate for every type of diarrhea, and there are specific situations where you should avoid it entirely.
Bismuth Subsalicylate: A Milder Alternative
Bismuth subsalicylate, the active ingredient in Pepto-Bismol and Kaopectate, works differently from loperamide. Rather than slowing your gut, it reduces fluid secretion into the intestine, lowers inflammation, and can even kill some of the bacteria causing the problem. That triple action makes it a reasonable first choice for mild diarrhea, especially when nausea or an upset stomach is part of the picture.
One harmless but startling side effect: it can turn your tongue and stool black. This is temporary and clears up within a few days of stopping the medication. Because bismuth subsalicylate contains a compound related to aspirin, it’s not safe for anyone who needs to avoid salicylates.
When Diarrhea Needs a Prescription
If diarrhea is a recurring problem rather than a one-off illness, over-the-counter options may not be enough. For irritable bowel syndrome with diarrhea (IBS-D), doctors can prescribe eluxadoline, a controlled medication that decreases bowel activity and targets the chronic cramping and urgency that come with IBS-D. Some people taking eluxadoline still use loperamide occasionally for breakthrough episodes.
Traveler’s diarrhea is another situation where prescription medication may be warranted. The CDC classifies traveler’s diarrhea by how much it disrupts your day. Mild cases that don’t interfere with your plans can be managed with bismuth subsalicylate or loperamide alone. Moderate cases, where symptoms are distressing or disrupt activities, may call for an antibiotic. Severe or incapacitating diarrhea, including any case involving bloody stool, generally requires antibiotic treatment. Azithromycin is the preferred first-line antibiotic for traveler’s diarrhea, particularly in regions like Southeast Asia where other antibiotics face resistance problems. Loperamide can be used alongside antibiotics to get faster symptom relief, but it shouldn’t be the only treatment when the diarrhea is severe or bloody.
When to Avoid Antidiarrheal Medication
Antidiarrheals work by slowing things down, which is exactly what you don’t want when your body is trying to flush out a dangerous infection. You should not take loperamide if you have severe diarrhea that started after a course of antibiotics, as this can be a sign of a serious bacterial overgrowth in the colon that needs medical treatment rather than symptom suppression. The same applies during a flare-up of an inflammatory bowel condition like ulcerative colitis.
Blood in your stool combined with a fever are red flags. These can signal dysentery or an invasive bacterial infection where trapping the pathogen in your gut could make things significantly worse. If you’ve recently traveled abroad and developed diarrhea, it’s also worth getting a medical opinion before reaching for loperamide, since tropical infections sometimes require specific treatment.
Probiotics as a Supplement
Probiotics aren’t medications in the traditional sense, but certain strains have genuine evidence behind them for shortening bouts of acute diarrhea. The two best-studied strains are Lactobacillus rhamnosus GG and Saccharomyces boulardii, a beneficial yeast. In clinical trials, S. boulardii was associated with stool consistency returning to normal roughly 15 hours sooner than placebo. A large meta-analysis found that S. boulardii combined with zinc supplementation outperformed standard treatment, zinc alone, or other probiotic strains at reducing how long diarrhea lasted.
Probiotics are most useful as an add-on rather than a replacement for other treatments. They won’t stop an acute episode as quickly as loperamide, but they may help your gut recover faster, particularly after infections or antibiotic use.
Diarrhea Medication and Children
The rules are very different for kids. Antidiarrheal medications, including both loperamide and bismuth subsalicylate, are not recommended for infants or young children. The risks outweigh the benefits at young ages. Loperamide in particular can worsen certain types of diarrhea in children, and any antidiarrheal agent can mask worsening symptoms that would otherwise prompt timely medical care. For children, the priority is preventing dehydration through oral rehydration solutions rather than stopping the diarrhea itself with medication.