Can Cephalexin Cause Diarrhea? Understanding the Side Effects

October 11, 2025 •

4 min read

Approximately one in five people who take antibiotics experience antibiotic-associated diarrhea, a common side effect of medications like cephalexin. This gastrointestinal upset occurs when the antibiotic disrupts the delicate balance of beneficial bacteria in your gut. While often mild and temporary, it's crucial to understand the risks and proper management.

Quick Summary

Cephalexin can cause diarrhea by disrupting the gut's normal bacteria. While typically mild, a more severe form called C. diff infection is a a rare risk. Taking the medication with food, staying hydrated, and using probiotics can help manage symptoms, but severe or bloody diarrhea requires immediate medical attention.

Key Points

Common Side Effect: Cephalexin, like other antibiotics, commonly causes diarrhea by disrupting the natural balance of gut bacteria.
Mild Diarrhea Management: Mild diarrhea can be managed by taking cephalexin with food, staying hydrated, and eating bland foods like those in the BRAT diet.
Serious C. diff Risk: A more serious, though rare, complication is C. difficile infection, which involves severe cramping, fever, and potentially bloody diarrhea.
Probiotic Usage: Probiotics can help restore beneficial gut bacteria, but they should be taken at least 1-2 hours apart from the cephalexin dose for maximum efficacy.
Know When to Call a Doctor: Seek immediate medical attention if you experience severe, bloody, or persistent diarrhea, as it could indicate a C. difficile infection.

Cephalexin is a commonly prescribed antibiotic belonging to the cephalosporin class, used to treat various bacterial infections, such as those affecting the respiratory tract, skin, and urinary tract. While highly effective at eliminating harmful bacteria, it also has a significant impact on the body's natural microbiome, particularly in the gut. This disruption is the primary reason that can cephalexin cause diarrhea, a frequently reported side effect. For most, this issue is mild and resolves after completing the medication. However, in rare cases, it can escalate into a more severe condition caused by an overgrowth of Clostridioides difficile, or C. diff.

How Cephalexin Disrupts the Gut Microbiome

The human digestive tract contains trillions of bacteria, collectively known as the gut microbiome, which are vital for digestion, immunity, and overall health. Antibiotics work by targeting and killing the bacteria responsible for an infection. However, many, including cephalexin, are broad-spectrum, meaning they are not selective and eliminate both the 'bad' and 'good' bacteria.

When cephalexin destroys beneficial bacteria in the gut, it creates an imbalance. The reduction of these protective bacteria allows other microorganisms, including harmful ones, to proliferate. This overgrowth and the resulting inflammatory response can lead to the classic symptoms of antibiotic-associated diarrhea (AAD), which include loose, watery stools and abdominal discomfort.

Recognizing Mild vs. Serious Diarrhea

It is crucial to distinguish between the typical, mild diarrhea associated with cephalexin and the rare but serious complication of C. diff infection.

Mild Antibiotic-Associated Diarrhea

Onset: Can begin shortly after starting the antibiotic or within a few days.
Duration: Typically resolves within a few days to a week after finishing the course of medication.
Symptoms: Loose stools, frequent bowel movements, and mild stomach cramping.

C. difficile-Associated Diarrhea (CDAD)

Onset: Can occur during antibiotic treatment or up to two months after the course is completed.
Duration: Requires specific treatment and may persist longer than mild AAD.
Symptoms: Frequent, watery, or bloody diarrhea; severe abdominal cramping and pain; fever; nausea; and loss of appetite.

Managing and Preventing Diarrhea from Cephalexin

For mild antibiotic-associated diarrhea, several strategies can help manage symptoms and promote gut health:

Take the medication with food: This is a straightforward way to reduce general stomach upset.
Stay hydrated: Diarrhea leads to fluid loss, so it is essential to drink plenty of water and electrolyte-rich fluids like broth or sports drinks.
Follow the BRAT diet: Eating bland foods like bananas, rice, applesauce, and toast can be gentle on the digestive system and help firm up stools.
Consider a probiotic supplement: Probiotics can help restore the beneficial bacteria in your gut. It is important to separate the probiotic dose from the antibiotic dose by at least 1-2 hours to prevent the antibiotic from killing the good bacteria.
Avoid trigger foods: Temporarily cut out dairy products, spicy food, and high-fiber foods, which can exacerbate diarrhea.

Comparison of Mild AAD vs. C. diff Diarrhea


Feature	Mild Antibiotic-Associated Diarrhea	C. difficile Diarrhea (CDAD)
Symptom Severity	Generally mild	Can be severe and potentially life-threatening
Onset	During or shortly after treatment	During treatment or up to 2 months after stopping
Primary Cause	Disruption of normal gut flora balance	Overgrowth of toxin-producing C. difficile bacteria
Associated Symptoms	Loose stools, mild cramping	Severe cramping, fever, bloody stools, nausea
Recommended Action	Manage with hydration, diet, probiotics	Seek immediate medical attention; may require different antibiotics
Antidiarrheals	Use with caution, but often not needed	AVOID, unless advised by a doctor, as it can worsen the condition

The Role of Probiotics

For those who frequently experience diarrhea with antibiotics, probiotics can be a helpful preventative measure. Probiotics are live microorganisms that supplement the body's store of beneficial bacteria. By introducing these microbes, you can help maintain a healthier gut flora balance during and after antibiotic treatment.

While studies show that probiotics can be effective in reducing the risk of AAD, their timing is key. Taking a probiotic at the same time as an antibiotic is counterproductive because the antibiotic will destroy the probiotic's live organisms. A common recommendation is to take the probiotic 1-2 hours after your cephalexin dose to ensure it is effective. Some of the best-studied strains for this purpose include Lactobacillus rhamnosus, Saccharomyces boulardii, and various Bifidobacterium species.

Conclusion

In conclusion, it is well-documented that cephalexin can cause diarrhea as a side effect, ranging from mild antibiotic-associated diarrhea to the more serious C. difficile infection. Most cases of mild diarrhea can be effectively managed with simple lifestyle and dietary changes, including taking the medication with food, staying hydrated, and adopting a bland diet. Using probiotics is also a viable strategy to help restore gut balance, but proper timing is essential to avoid destroying the beneficial microorganisms. However, it is paramount to recognize the red flags of a severe C. difficile infection—such as watery or bloody diarrhea, severe cramping, and fever—and seek immediate medical attention if they appear. Always consult with your healthcare provider for personalized advice on how to manage any medication side effects.

Learn more about antibiotic-associated diarrhea and its causes from the Mayo Clinic.

Frequently Asked Questions

Mild diarrhea from cephalexin usually lasts for a few days to a week and typically resolves after you complete the full course of your medication. If it persists or is severe, contact your doctor.

You should not take anti-diarrhea medication without consulting your doctor first, especially if you suspect C. difficile. These medications can trap toxins in your intestines, making the condition worse.

Mild diarrhea is a temporary upset caused by gut flora imbalance, while C. difficile diarrhea is a more severe infection that can cause bloody stools, high fever, and intense abdominal pain. C. diff can also occur weeks after finishing the antibiotic.

Taking cephalexin with food can help minimize stomach upset and is recommended, especially for those prone to gastrointestinal side effects. It does not significantly affect the drug's absorption.

Yes, children can also experience diarrhea from cephalexin, and the management principles are similar. However, a pediatrician should be consulted before giving any over-the-counter medication or for severe symptoms.

Commonly recommended strains include Lactobacillus rhamnosus, Saccharomyces boulardii, and various Bifidobacterium species. However, always consult a healthcare provider for personalized recommendations and ensure you space the probiotic dose from the antibiotic.

It's best to avoid rich, spicy, or high-fiber foods that might aggravate your digestive system. Some people also find it helpful to temporarily reduce their intake of dairy products.