Roughly 5% to 25% of people taking antibiotics develop diarrhea, making it one of the most common side effects of antibiotic treatment. Some classes of antibiotics are far more likely to cause it than others, and understanding which ones carry the highest risk can help you know what to expect during a course of treatment.
Which Antibiotics Are Most Likely To Cause It
Three antibiotic classes stand out for their association with diarrhea: aminopenicillins, cephalosporins, and clindamycin. Aminopenicillins include widely prescribed drugs like amoxicillin, especially when combined with clavulanate (the combination often sold as Augmentin). This combination is one of the most frequently prescribed antibiotics in the world, and its diarrhea rates are notably higher than amoxicillin alone because clavulanate itself irritates the gut.
Cephalosporins are a broad family of antibiotics used for everything from ear infections to surgical prophylaxis. Broader-spectrum versions tend to cause more gut disruption because they wipe out a wider range of bacteria. Clindamycin, a lincosamide antibiotic often used for skin and dental infections, carries one of the highest diarrhea risks of any oral antibiotic and is also strongly linked to more serious gut infections.
Fluoroquinolones and macrolides (like azithromycin and erythromycin) also cause diarrhea, though generally at lower rates. Erythromycin is a special case: it directly stimulates the muscles of the gut, producing cramping and loose stools through a mechanism that has nothing to do with bacteria at all. Tetracyclines, by contrast, are the class least associated with gut complications.
Why Antibiotics Disrupt Your Gut
Your intestines host trillions of bacteria that help digest food, produce vitamins, and keep harmful organisms in check. Antibiotics can’t distinguish between the bacteria causing your infection and the beneficial ones living in your gut, so they reduce both populations. When those helpful bacteria are depleted, several things go wrong at once.
Certain gut bacteria normally break down carbohydrates and fiber into compounds your colon can absorb. Without them, undigested sugars pull water into the intestine by osmosis, producing watery stools. At the same time, the ecological vacuum left behind gives opportunistic organisms room to multiply. The most dangerous of these is Clostridioides difficile (C. diff), a bacterium that produces toxins that inflame the colon lining. Some antibiotics also speed up gut motility directly, pushing food through before enough water can be reabsorbed.
The C. Difficile Connection
Most antibiotic-related diarrhea is mild and self-limiting. C. diff infection is the exception. It accounts for a minority of cases but can cause severe, even life-threatening colitis. A large Swedish population-based study found that lincosamides (clindamycin’s drug class) carried one of the highest risks, with an adjusted odds ratio of 31.4 for C. diff infection. Combinations of penicillins, sulfonamides with trimethoprim, and cephalosporins also showed significantly elevated risk.
Interestingly, tetracyclines were the only antibiotic class that showed no increased C. diff risk after adjusting for other factors. This makes them something of an outlier in the antibiotic world when it comes to gut safety. Hospitalized patients, older adults, and people who have taken multiple rounds of antibiotics are at the greatest risk for C. diff, since their gut flora may already be compromised before the new course begins.
When Diarrhea Starts and How Long It Lasts
Mild antibiotic-associated diarrhea can begin within hours of your first dose or develop over the first few days. In most cases, it resolves on its own within a few days of continuing the antibiotic or shortly after finishing the course. This type usually involves loose stools a few extra times per day without fever or significant cramping.
More serious diarrhea, particularly when caused by C. diff, often follows a different timeline. It can begin days to two full months after starting the antibiotic, which means symptoms sometimes appear after you’ve already finished your prescription. Up to 38% of antibiotic-associated diarrhea cases are “delayed” in this way, starting only after the course is complete. This delayed pattern catches many people off guard because they don’t connect their symptoms to a medication they stopped taking weeks earlier.
Who Is at Higher Risk
Not everyone taking the same antibiotic will have the same gut reaction. Several factors raise your chances:
- Age: Older adults and very young children are more vulnerable, partly because their gut flora is less resilient or less fully established.
- Hospitalization: Healthcare-associated outbreaks drive diarrhea rates as high as 26% to 60%, far above the 5% to 25% seen in outpatient settings. Proximity to other patients carrying C. diff and exposure to more aggressive antibiotics both contribute.
- Broad-spectrum antibiotics: The wider the range of bacteria an antibiotic kills, the more collateral damage to your gut ecosystem.
- Multiple or prolonged courses: Each round of antibiotics further depletes your beneficial bacteria, making subsequent disruption more likely.
- Previous antibiotic-associated diarrhea: If it has happened to you before, it is more likely to happen again.
Probiotics for Prevention
Taking a probiotic alongside your antibiotic is one of the most studied prevention strategies, and the evidence generally supports it. Two strains have the strongest track record: Lactobacillus rhamnosus GG and Saccharomyces boulardii, a strain of brewer’s yeast. For preventing general antibiotic-associated diarrhea, these two consistently outperform other strains in clinical trials. Lactobacillus casei may be the best option specifically for preventing C. diff-related diarrhea.
Dose matters. Preparations containing 5 to 40 billion colony-forming units (CFU) per day showed the best results. Lower doses (under 5 billion CFU) were still effective but required treating more patients to prevent one case of diarrhea. In studies of children, giving a probiotic during antibiotic treatment prevented diarrhea in roughly one out of every six children treated. Single-strain and multi-strain preparations performed similarly, so you don’t necessarily need a complex product.
The main caveat: people with weakened immune systems should avoid probiotic supplements, since the live organisms could theoretically cause infection in someone who can’t fight them off normally.
Managing Symptoms at Home
If you develop mild diarrhea while taking an antibiotic, hydration is the first priority. Water alone isn’t ideal because diarrhea depletes electrolytes. Broths, sports drinks, and oral rehydration solutions replace both fluid and minerals more effectively. For children, pediatric rehydration solutions are the safest option.
Over-the-counter antidiarrheal medications containing bismuth subsalicylate (the active ingredient in Pepto-Bismol) can help with mild symptoms in teenagers and adults. However, certain antidiarrheals should not be used if there’s any chance you have a C. diff or other bacterial gut infection, because slowing the gut down can trap toxins inside the colon and make the infection worse. If your diarrhea is severe, bloody, accompanied by fever, or started weeks after finishing your antibiotic, those are signs of a more serious problem that needs medical evaluation rather than home management.
Can You Reduce Your Risk Before Starting?
The single most effective strategy is using the narrowest-spectrum antibiotic that will treat your infection. Broad-spectrum antibiotics are sometimes necessary, but when a targeted option exists, it spares more of your beneficial gut bacteria. This is a conversation worth having with whoever prescribes your antibiotic, especially if you have a history of gut trouble with past courses.
Starting a probiotic on the same day you begin your antibiotic, rather than waiting for symptoms to appear, gives the protective bacteria the best chance of establishing themselves before your gut flora is disrupted. Take the probiotic a few hours apart from the antibiotic dose so the antibiotic doesn’t immediately kill the probiotic organisms. Continue the probiotic for at least a few days after finishing the antibiotic course, since your gut flora remains vulnerable during recovery.