The most effective over-the-counter medicine for diarrhea is loperamide (sold as Imodium), which works within about one hour and can control symptoms for up to three days. Bismuth subsalicylate (Pepto-Bismol) is the other main OTC option, working through a different mechanism that’s especially useful when nausea or an upset stomach accompanies the diarrhea. Which one you reach for depends on your symptoms, their severity, and what’s causing them.
Loperamide: The Fastest OTC Option
Loperamide slows down the muscle contractions in your intestines, giving your body more time to absorb water and electrolytes from food as it passes through. It also increases muscle tone in the rectum, which helps you feel less urgency. The result is firmer stools and fewer trips to the bathroom.
For adults using the OTC version, the FDA-approved maximum is 8 mg per day (16 mg per day if prescribed by a doctor). If your diarrhea hasn’t improved after two days of use, stop taking it and talk to a healthcare provider. Taking more than the recommended dose is dangerous: the FDA has specifically warned that exceeding the labeled amount can cause severe heart rhythm problems or death, which is why packaging now limits the number of doses per box.
Loperamide works well for garden-variety loose stools, like those triggered by stress, dietary changes, or mild stomach bugs. It’s not the right choice when diarrhea is accompanied by high fever or bloody stools, because in those cases your body may be using diarrhea to flush out a harmful infection, and slowing that process down can make things worse.
Bismuth Subsalicylate: For Diarrhea With Nausea
Bismuth subsalicylate takes a different approach. Rather than slowing gut movement, it reduces the amount of fluid your intestines secrete while also fighting bacteria that may be contributing to the problem. Its antimicrobial properties prevent bacteria from binding to the stomach and intestinal lining, which helps reduce inflammation and promote fluid absorption. This dual action makes it particularly useful for traveler’s diarrhea or food-related illness where bacterial contamination is likely.
One important caveat: bismuth subsalicylate contains a compound related to aspirin. Because of the risk of Reye syndrome, a rare but serious condition, it’s not routinely recommended for children. The American Academy of Pediatrics has noted that there isn’t enough data to rule out this risk in kids receiving salicylate-based treatments. It can also temporarily turn your tongue and stools black, which is harmless but surprising if you’re not expecting it.
Prescription Medicines for Persistent Diarrhea
When OTC options aren’t enough, doctors sometimes prescribe a combination medication containing diphenoxylate and atropine (commonly known as Lomotil). This is typically reserved for adults and children 13 and older whose diarrhea hasn’t responded to other treatments, or as an add-on therapy for conditions like irritable bowel syndrome, ulcerative colitis, or Crohn’s disease. Diphenoxylate works similarly to loperamide by slowing intestinal movement, but it’s stronger. The atropine is added in a small dose specifically to discourage misuse: at higher-than-prescribed amounts, it causes unpleasant side effects like nausea, bloating, rapid heartbeat, and dry mouth. The combination is classified as a Schedule V controlled substance, meaning it has minimal abuse potential but still requires a prescription and medical supervision for long-term use.
Antibiotics for Bacterial and Traveler’s Diarrhea
Antibiotics only help when bacteria are the cause, which is most common with traveler’s diarrhea or confirmed bacterial infections. They’re never appropriate for viral stomach bugs, which are the most common cause of acute diarrhea in everyday life.
For traveler’s diarrhea that’s moderate to severe (meaning it disrupts your activities or leaves you unable to function), the CDC recommends antibiotic treatment. Azithromycin is the preferred first-line option, especially for diarrhea acquired in Southeast Asia or other regions where certain antibiotic-resistant bacteria are common. It’s also the go-to choice when diarrhea includes fever or bloody stools. Fluoroquinolone antibiotics are another option, often effective as a single dose for moderate cases. Rifaximin, a gut-specific antibiotic, is approved specifically for diarrhea caused by noninvasive strains of E. coli but isn’t appropriate when more aggressive bacterial infections are suspected.
These antibiotics can be combined with loperamide for faster symptom relief. Parasitic causes like Giardia require different medications entirely, which is one reason persistent diarrhea after travel warrants a stool test rather than self-treatment.
Probiotics as a Supplement
One probiotic with the most clinical backing for diarrhea is Saccharomyces boulardii, a live yeast that’s been used for over 30 years as a therapeutic agent for diarrheal diseases. Clinical trials support its use for antibiotic-associated diarrhea, acute infectious diarrhea, traveler’s diarrhea, and diarrhea related to C. difficile infections. It’s available without a prescription as a dietary supplement. Probiotics work best as a complement to other treatment rather than a standalone solution, and they tend to shorten the duration of illness rather than stop symptoms immediately.
Rehydration Matters More Than Medicine
No matter which medicine you use, replacing lost fluids is the single most important part of managing diarrhea. Dehydration, not the diarrhea itself, is what makes the condition dangerous. Water alone isn’t ideal because diarrhea also drains sodium, potassium, and other electrolytes your cells need to absorb fluid properly.
Oral rehydration solutions are specifically designed to exploit how your intestines absorb water. The key is the ratio of sodium to glucose: research shows the optimal range falls between 0.64 and 0.82. Within that window, your intestinal cells shift from secreting fluid (which worsens diarrhea) to actively absorbing it. Solutions recommended by the European Society for Pediatric Gastroenterology use about 60 milliequivalents per liter of sodium and 80 to 111 millimoles per liter of glucose, hitting that sweet spot. Store-bought oral rehydration solutions like Pedialyte or Drip Drop are formulated to match these ratios. Sports drinks contain too much sugar and too little sodium to work as well.
Signs That Need Medical Attention
Most acute diarrhea resolves on its own within a few days. But certain symptoms signal something more serious. For adults, these include diarrhea lasting more than two days without improvement, signs of dehydration (excessive thirst, dark urine, dizziness, very little urination), severe abdominal or rectal pain, bloody or black stools, and fever above 102°F.
Children need attention sooner. In kids, diarrhea that doesn’t improve within 24 hours, no wet diaper for three or more hours, fever above 102°F, bloody stools, or unusual drowsiness all warrant a call to the pediatrician. Physical signs of dehydration in children include sunken eyes or cheeks, a sunken soft spot on an infant’s head, and skin that stays tented when you gently pinch it rather than springing back flat.