Yes, diarrhea is one of the most common side effects of amoxicillin. Roughly 1 in 20 people taking amoxicillin will experience it, and the risk jumps significantly with amoxicillin-clavulanate (the combination sold as Augmentin), where about 1 in 8 people develop diarrhea during treatment. In most cases it’s mild and resolves on its own, but there are a few things worth knowing about why it happens, how to manage it, and when it signals something more serious.
Why Amoxicillin Causes Diarrhea
Amoxicillin is a broad-spectrum antibiotic, which means it doesn’t just target the bacteria causing your infection. It also kills off beneficial bacteria in your gut. Your intestines rely on a diverse community of microbes to absorb water, break down food, and keep digestion running smoothly. When antibiotics thin out that community, the balance shifts and diarrhea often follows.
A 2022 study from MIT pinpointed one bacterial family in particular. People who developed diarrhea while taking amoxicillin-clavulanate had significantly lower levels of a group of gut bacteria called Ruminococcaceae, both before and during treatment. These bacteria play a central role in maintaining gut health, so people who start with lower levels appear more vulnerable to antibiotic-related digestive problems. The finding helps explain why some people get diarrhea from the same antibiotic course that causes no issues for someone else.
Plain Amoxicillin vs. Amoxicillin-Clavulanate
The distinction matters. Plain amoxicillin carries a moderate diarrhea risk, with studies showing rates around 5 to 10 percent. Amoxicillin-clavulanate pushes that number to about 17.5 percent in pooled clinical data, roughly triple the rate seen in placebo groups. Clavulanate, the added ingredient that helps the antibiotic overcome resistant bacteria, is the main driver of the extra gut disruption. If your prescription is for Augmentin or a generic amoxicillin-clavulanate and diarrhea becomes a problem, it’s worth asking your prescriber whether plain amoxicillin would be effective for your particular infection.
When Diarrhea Typically Starts
Antibiotic-related diarrhea can begin at any point during your course of treatment, sometimes within the first day or two. It can also show up after you’ve finished the full course, since the gut microbiome takes time to recover. Most mild cases clear up within a few days of stopping the medication. If your diarrhea persists beyond two days, or if it’s accompanied by fever, severe abdominal pain, blood in the stool, or signs of dehydration, those are signals that something beyond routine antibiotic disruption may be going on.
How to Manage It
For mild diarrhea, the priority is staying hydrated. Water is your best option, along with fluids that contain electrolytes like broth or sports drinks. Oral rehydration solutions work well too. Avoid fruit juice and soft drinks, which can pull more water into the intestines and make things worse.
Eating bland, easy-to-digest foods can help. Rice, bananas, toast, and plain crackers are gentle on an irritated gut. You don’t need to follow a rigid diet, but cutting back on high-fiber, greasy, or spicy foods during treatment often makes a noticeable difference. Take your amoxicillin with food if you aren’t already, as this can reduce stomach upset.
One important note: don’t stop your antibiotic without talking to your prescriber first. Cutting a course short can leave the original infection partially treated, which risks a relapse or contributes to antibiotic resistance. If the diarrhea is mild and you’re otherwise feeling fine, completing the full course is generally the right call.
Do Probiotics Help?
The evidence is promising but not airtight. In studies focused on preventing antibiotic-associated diarrhea, high-dose probiotics (5 billion colony-forming units or more per day) were more effective than lower doses. The two strains with the strongest evidence are Saccharomyces boulardii and Lactobacillus rhamnosus, at doses ranging from 5 to 40 billion CFUs per day. In pooled data, you’d need to treat about 6 people with high-dose probiotics to prevent one case of antibiotic diarrhea, and probiotics may shorten the duration by roughly a day.
For adults, trying a probiotic supplement alongside your antibiotic is unlikely to cause harm. People with weakened immune systems should avoid probiotic supplements, however, because the live organisms can occasionally cause infections in that group. For children, it’s best to check with their pediatrician before adding anything to the regimen.
Diarrhea in Children on Amoxicillin
Amoxicillin is one of the most commonly prescribed antibiotics for kids, and about 1 in 5 children who take any antibiotic will develop diarrhea. Children under two are especially prone. If the diarrhea is mild and your child is otherwise acting normally, you can manage it at home. Offer water frequently rather than juice. If your child is in diapers, the frequent loose stools can quickly cause a painful rash. Wash the area gently with water, pat dry, and apply a barrier cream like petroleum jelly or zinc oxide after each change.
Don’t give children anti-diarrheal medications like loperamide unless specifically directed by a doctor. These drugs slow gut motility, which can worsen inflammation if there’s a more serious process happening in the intestines. For infants, oral rehydration solutions designed for children (like Pedialyte) are preferable to water alone because they replace both fluids and electrolytes in the right proportions.
When Diarrhea Signals a Bigger Problem
In rare cases, antibiotic use can trigger an overgrowth of a harmful bacterium called Clostridioides difficile (C. diff). This happens when antibiotics clear out enough of the normal gut bacteria that C. diff, which is naturally resistant to many antibiotics, multiplies unchecked. Amoxicillin carries a lower C. diff risk compared to some other antibiotics like fluoroquinolones or clindamycin, but the risk isn’t zero.
C. diff diarrhea tends to be more severe: watery, frequent (sometimes 10 or more times a day), and often accompanied by cramping, fever, and occasionally blood or mucus. If your diarrhea is worsening rather than improving, lasts more than two days, or comes with any of those additional symptoms, contact your healthcare provider. Stools that are black, tarry, or bloody always warrant a call. C. diff requires specific treatment, and catching it early leads to better outcomes.