Diarrhea after antibiotics is common, and a loose stool or mild stomach upset does not always mean something is seriously wrong. Antibiotics can change the balance of bacteria in the gut, which may lead to loose or watery bowel movements, cramping, gas, or nausea. However, diarrhea during or after an antibiotic course can also be a sign of Clostridioides difficile, often called C. diff, an infection that can cause inflammation of the colon. [1][2]

The key point: let the clinician who prescribed the antibiotic know about new diarrhea, especially if it is frequent, watery, worsening, or continues after the antibiotic is finished. Seek medical care promptly for dehydration, blood in the stool, black tarry stool, fever, severe abdominal pain, or frequent vomiting. [1][2]

Why antibiotics can cause diarrhea

Antibiotics treat bacterial infections, but they can also affect helpful bacteria that normally live in the intestines. This shift can change how the gut digests food and handles fluid, causing diarrhea as a medication side effect. Diarrhea can also happen for another reason at the same time, such as a viral stomach illness, food poisoning, a new food intolerance, or another medicine. [2]

Many cases are mild and improve without specific treatment. Mild antibiotic-associated diarrhea may settle while treatment continues or shortly after the course ends. Still, it is important not to assume that every case is harmless, particularly when symptoms are significant or are getting worse. [3]

Could it be C. diff?

C. diff is a bacterium that can cause diarrhea and colitis, which is inflammation of the colon. Antibiotics raise the risk because they can reduce some of the gut bacteria that help keep C. diff from overgrowing. Most cases happen while a person is taking antibiotics or soon afterward, although the effects of antibiotics on the gut microbiome can last for months. [1]

Not everyone with diarrhea after antibiotics has C. diff. However, CDC advises people who develop diarrhea while taking antibiotics or after recently finishing them to contact a healthcare professional to discuss their symptoms and whether evaluation is needed. [1]

Symptoms that can occur with C. diff

• Watery diarrhea, often more than a person’s usual bowel pattern
• Abdominal cramping, tenderness, or pain
• Fever
• Nausea or loss of appetite
• Dehydration or feeling weak, dizzy, or lightheaded

C. diff can affect anyone, but risk is higher in people age 65 or older, people with a weakened immune system, people with a prior C. diff infection, and people who have recently been in a hospital, nursing home, or other healthcare setting. Taking a longer course of antibiotics may also increase risk. [1]

What to do if you have diarrhea after antibiotics

1. Do not stop or change the antibiotic on your own

Continue taking the antibiotic exactly as prescribed unless the prescribing clinician tells you otherwise. Stopping early, skipping doses, or saving leftover antibiotics can leave an infection undertreated and may cause other problems. Contact the prescriber, pharmacist, or another healthcare professional for advice about the diarrhea and whether the medication plan needs to change. [1][7]

2. Focus on fluids and electrolytes

Diarrhea can remove both fluid and electrolytes, which are minerals the body needs to function normally. Drink regularly, taking small, frequent sips if your stomach feels unsettled. Water, broth, and oral rehydration solutions can be helpful. Oral rehydration solutions contain a balance of glucose and electrolytes designed to replace losses from diarrhea. [4]

Older adults and people with kidney disease, diabetes, heart failure, a weakened immune system, or other ongoing health conditions should check with a clinician about the best fluid choices and amounts for them. [4]

3. Eat as you are able

You do not need to force food if you have little appetite for a short time. When you feel ready to eat, many people tolerate small, simple meals better than large or high-fat meals. You can usually return to your usual diet as your appetite returns. If dairy, greasy foods, alcohol, caffeine, or very spicy foods clearly make symptoms worse, it is reasonable to avoid them temporarily. [4]

4. Be careful with over-the-counter diarrhea medicines

Adults can sometimes use over-the-counter antidiarrheal medicines for uncomplicated acute diarrhea, but they are not right for every situation. Do not use these medicines without medical advice if you have fever, bloody stools, black tarry stools, severe abdominal pain, a swollen abdomen, or concern for a serious intestinal infection such as C. diff. They are also generally not recommended for infants, toddlers, and young children without guidance from a clinician. [4]

Read the Drug Facts label carefully, follow the label directions, and ask a pharmacist before using an antidiarrheal medicine if you take other medications, are pregnant, have liver disease, or have a chronic health condition. Do not take more than the labeled amount.

5. Do not rely on probiotics as treatment

Probiotics are live microorganisms sold in foods and supplements. Some people take them during or after antibiotics, but the evidence is mixed and depends on the specific product and situation. NIDDK notes that many doctors and professional societies do not believe current evidence supports probiotics for treating or preventing diarrhea. Talk with a healthcare professional before using a probiotic, especially if you are immunocompromised, seriously ill, or have a central venous catheter. [4]

When to contact your primary care clinician or prescriber

Contact the prescribing clinician or your primary care office promptly if diarrhea starts during an antibiotic course or after you finish one. They can help determine whether you can monitor symptoms at home, need an office or urgent care evaluation, or need testing.

Make contact the same day if you have any of the following:

• Three or more watery or loose stools in a day that are new for you
• Diarrhea that is worsening or not beginning to improve
• Diarrhea lasting more than 2 days
• Six or more loose stools in 24 hours
• Fever, chills, nausea, or worsening cramps
• Symptoms of dehydration, such as very dry mouth, dark urine, urinating less than usual, dizziness, or unusual fatigue
• Age 65 or older, pregnancy, a weakened immune system, inflammatory bowel disease, kidney disease, or another condition that raises the risk of complications
• A recent hospitalization, nursing-home stay, or past C. diff infection

Diarrhea can become more serious more quickly in infants and young children. Contact a child’s pediatric clinician promptly for diarrhea in an infant, diarrhea lasting more than a day in a child, fever, poor drinking, fewer wet diapers, no tears when crying, unusual sleepiness, or any concern that the child is becoming dehydrated. [2]

When urgent care may be appropriate

Urgent care can be a reasonable option when you cannot reach your usual clinician promptly and you have new diarrhea after antibiotics that needs same-day assessment but you do not have emergency symptoms. Examples include persistent watery diarrhea, mild to moderate dehydration symptoms, a fever, significant cramping, or concern for C. diff.

A clinician may ask about the antibiotic you took, when symptoms began, your recent healthcare exposure, travel, other medicines, and how often you are having bowel movements. Depending on your symptoms, they may examine you, check for dehydration, and order a stool test for C. diff or other causes of diarrhea. Testing is most useful when someone has compatible symptoms; a positive C. diff test without symptoms does not necessarily mean active infection. [1]

When to seek emergency care or call 911

Go to an emergency department now, or call 911 if you or someone else has diarrhea after antibiotics along with any of these warning signs:

• Confusion, fainting, inability to stay awake, a seizure, or unresponsiveness
• Signs of severe dehydration, such as severe weakness, inability to stand safely, very little or no urine, or inability to keep fluids down
• Severe or rapidly worsening abdominal pain
• A very swollen, hard, or tender abdomen
• Vomiting blood, passing a large amount of blood, or black, tarry stool
• Rapid deterioration, severe illness, or symptoms that feel life-threatening

These symptoms can signal severe dehydration, significant bleeding, a serious infection, or another urgent condition. Do not wait for a routine appointment if they occur. [2][6]

How C. diff is diagnosed and treated

If a clinician suspects C. diff, they usually review your symptoms and medical history and may order a laboratory test on a stool sample. A stool test can help identify C. diff or its toxins, but results must be interpreted along with symptoms. [1]

If C. diff is diagnosed, treatment commonly includes a prescription antibiotic that specifically targets the infection. The clinician may also decide whether it is safe to stop or switch the original antibiotic that may have contributed to the problem. Severe illness may require treatment in the hospital, including fluids through a vein and monitoring. [1]

Do not take leftover antibiotics or someone else’s medication in an attempt to treat diarrhea or suspected C. diff. The correct treatment depends on the cause and your overall health.

Preventing the spread of C. diff at home

Most diarrhea after antibiotics is not caused by C. diff. But if C. diff is diagnosed or strongly suspected, take extra steps to reduce spread in the household:

• Wash hands with soap and water after using the bathroom and before eating or preparing food.
• Ask caregivers and household members to do the same. Soap and water is especially important for reducing spread of C. diff.
• If possible, use a separate bathroom while you have active diarrhea.
• Clean commonly touched bathroom surfaces, such as toilet handles, toilet seats, faucets, and doorknobs.
• Wash soiled clothing, towels, and bedding separately using the hottest water safe for the items. Follow product directions if using bleach or a disinfectant.

CDC recommends cleaning first and then using an appropriate disinfectant. Follow label directions carefully, and never mix cleaning products. [5]

What to expect

Mild diarrhea after antibiotics may improve as your digestive system recovers, but the timing varies. Keep track of when the antibiotic started and ended, the number of loose stools each day, your temperature, abdominal symptoms, and how much you are drinking and urinating. This information can make it easier for a clinician to assess you.

Follow up if symptoms are not improving, return after getting better, or interfere with hydration, sleep, work, or daily activities. If you have already been treated for C. diff and develop new diarrhea later, contact your clinician because repeat infections can occur. [1]

References

1. Centers for Disease Control and Prevention. About C. diff. Updated May 13, 2026. Available from: https://www.cdc.gov/c-diff/about/index.html
2. National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms & causes of diarrhea. Available from: https://www.niddk.nih.gov/health-information/digestive-diseases/diarrhea/symptoms-causes
3. Mayo Clinic. Antibiotic-associated diarrhea: Diagnosis & treatment. Available from: https://www.mayoclinic.org/diseases-conditions/antibiotic-associated-diarrhea/diagnosis-treatment/drc-20352237
4. National Institute of Diabetes and Digestive and Kidney Diseases. Treatment of diarrhea. Available from: https://www.niddk.nih.gov/health-information/digestive-diseases/diarrhea/treatment
5. Centers for Disease Control and Prevention. Preventing C. diff. Updated December 18, 2024. Available from: https://www.cdc.gov/c-diff/prevention/index.html
6. MedlinePlus. Dehydration. Updated July 13, 2025. Available from: https://medlineplus.gov/ency/article/000982.htm
7. Centers for Disease Control and Prevention. Healthy habits: Antibiotic do’s and don’ts. Updated October 31, 2025. Available from: https://www.cdc.gov/antibiotic-use/about/index.html