Does Bactrim cause diarrhea? A look at antibiotic side effects

October 12, 2025 •

4 min read

It's estimated that between 5 and 25 percent of adults may experience diarrhea while taking antibiotics. The question, Does Bactrim cause diarrhea?, is a common concern for patients, and the answer is yes, it is a possible side effect of this medication. This article explores the mechanisms behind antibiotic-associated diarrhea and how to manage and prevent it.

Quick Summary

Bactrim can cause diarrhea by disrupting the natural balance of gut bacteria. This can result in mild, temporary gastrointestinal upset or, in more severe cases, a Clostridioides difficile (C. diff) infection. Understanding the causes, recognizing symptoms, and knowing when to seek medical help are crucial for safe treatment.

Key Points

Diarrhea is a known side effect: Yes, Bactrim can cause diarrhea by altering the natural balance of gut bacteria.
Two types of diarrhea can occur: The diarrhea can be a mild, temporary condition or a more severe infection caused by Clostridioides difficile (C. diff).
Seek immediate medical help for severe symptoms: If you experience bloody or watery stools, severe abdominal pain, or fever, contact a healthcare provider immediately.
Manage mild diarrhea with hydration and diet: For mild cases, focus on staying hydrated with fluids and electrolytes, and eat bland, easily digestible foods like the BRAT diet.
Probiotics can help, but timing is important: Taking probiotic supplements or eating probiotic-rich foods can help restore gut flora, but take them 1-2 hours apart from your Bactrim dose.
Complete the full antibiotic course: Never stop taking Bactrim early unless your doctor tells you to, as it can lead to drug-resistant bacteria.

The Link Between Antibiotics and Diarrhea

Antibiotics, including Bactrim (a combination of sulfamethoxazole and trimethoprim), are designed to kill bacteria. While they target harmful bacteria causing an infection, they also disrupt the delicate balance of beneficial bacteria living in your gut, known as the microbiome. When this balance is disturbed, it can lead to various gastrointestinal issues, with diarrhea being one of the most common. This condition is known as antibiotic-associated diarrhea (AAD).

The extent of gut flora disruption can lead to two different scenarios of diarrhea:

Mild to Moderate Diarrhea: This is the more common form of AAD. It typically begins shortly after starting the antibiotic and usually subsides once the treatment is finished. The symptoms are generally manageable and are caused by the temporary imbalance of intestinal bacteria.
Severe Diarrhea (Clostridioides difficile): In more serious cases, the disruption of the gut flora can allow an opportunistic bacterium called Clostridioides difficile (C. diff) to multiply uncontrollably. C. diff produces toxins that cause inflammation of the colon, leading to more severe and potentially life-threatening diarrhea. This can occur during treatment or up to two months after stopping the antibiotic.

How Bactrim Specifically Contributes to Diarrhea

Bactrim is a broad-spectrum antibiotic, meaning it affects a wide range of bacteria. This characteristic makes it particularly effective for treating various infections, such as urinary tract infections (UTIs) and bronchitis. However, this also means it can have a more significant impact on your gut's natural bacterial populations compared to a narrow-spectrum antibiotic. While studies suggest that the risk of C. diff infection with Bactrim may be lower compared to some other broad-spectrum antibiotics, it is still a documented risk.

Managing Mild Antibiotic-Associated Diarrhea

For mild cases of diarrhea caused by Bactrim, several at-home management strategies can help provide relief. It is crucial to remember that you should not stop your antibiotic course unless instructed by your doctor. Stopping early can lead to the infection returning or becoming resistant to the medication.

Here are some tips for managing mild diarrhea:

Stay Hydrated: Drink plenty of fluids, including water, broth, and electrolyte drinks, to replace lost fluids and prevent dehydration.
Follow the BRAT Diet: The BRAT diet consists of bland, easy-to-digest foods like bananas, rice, applesauce, and toast. These foods are low in fiber and can help firm up stools.
Consider Probiotics: Probiotic supplements or foods containing live, active cultures like yogurt and kefir can help restore the balance of beneficial bacteria in your gut. To avoid the antibiotic from killing the good bacteria, it is generally recommended to take probiotics at least 1 to 2 hours before or after your Bactrim dose.
Avoid Trigger Foods: Limit foods that can irritate the digestive system, such as spicy, greasy, high-sugar, or high-fiber foods. Caffeine and alcohol can also worsen diarrhea symptoms.

Comparison: Mild vs. Severe Diarrhea

Recognizing the difference between typical AAD and a more serious condition like C. diff is critical. The following table highlights the key distinctions:


Feature	Mild Antibiotic-Associated Diarrhea	Severe (C. diff) Diarrhea
Onset	Often starts early in treatment.	Can start during or weeks to months after antibiotic course.
Stool Characteristics	Loose, watery stools, often 1–2 per day.	Frequent, watery diarrhea. May contain blood or mucus.
Accompanying Symptoms	May include mild abdominal cramping.	Severe abdominal pain, cramping, fever, nausea, loss of appetite.
Management	At-home care: hydration, bland diet, probiotics.	Requires immediate medical attention and discontinuation of Bactrim.
Causative Agent	Disruption of normal gut flora.	Overgrowth of Clostridioides difficile bacteria producing toxins.

When to Contact a Healthcare Provider

It is essential to contact your doctor if you experience any of the following symptoms, as they could indicate a more serious issue like C. diff infection:

Diarrhea that is watery or bloody
Severe abdominal pain or cramping
A fever accompanying your diarrhea
Diarrhea that does not improve after the antibiotic course is finished or lasts more than a couple of days
Signs of dehydration, such as intense thirst, dizziness, or reduced urination

Do not take over-the-counter anti-diarrheal medications like Imodium without speaking to your doctor first, as they can sometimes worsen C. diff infection by preventing the body from expelling the toxins.

Long-Term Considerations

In rare cases, diarrhea caused by C. diff can lead to a long-term condition called pseudomembranous colitis, which involves significant inflammation of the colon. This is why seeking prompt medical advice for severe or persistent diarrhea is critical. For most people, mild AAD is a temporary inconvenience that resolves without complications. Maintaining a healthy lifestyle, including proper hydration and a balanced diet, can help support your gut health during and after antibiotic treatment.

Conclusion

In summary, Bactrim can and does cause diarrhea as a potential side effect due to its action on the gut microbiome. For most individuals, this is a mild and temporary issue that can be effectively managed with supportive measures like proper hydration and a bland diet. However, it is crucial to remain vigilant for signs of more severe, persistent diarrhea, fever, or bloody stools, which could signal a serious C. diff infection requiring immediate medical care. Always follow your doctor's instructions, complete the full course of your prescription, and consult with a healthcare professional if you have any concerns about side effects. By understanding the potential risks and appropriate management strategies, you can minimize discomfort while effectively treating your infection.

Frequently Asked Questions

Antibiotics cause diarrhea by disrupting the natural balance of good and bad bacteria in your gut. By killing off beneficial bacteria along with the harmful ones, it can cause digestive upset and lead to loose stools.

Yes, diarrhea is a common side effect of many antibiotics, including Bactrim. Most cases are mild and resolve after the medication is finished.

You should not take over-the-counter anti-diarrheal medicines like loperamide (Imodium A-D) without consulting your doctor first. In cases of C. diff infection, these medications can be harmful by preventing the body from eliminating toxins.

You should contact your doctor immediately if you have frequent or severe diarrhea, bloody or mucus-filled stools, severe abdominal pain, or a fever. These can be signs of a more serious infection.

Mild diarrhea typically stops shortly after completing the antibiotic course. However, diarrhea from a C. diff infection can occur weeks or even months after you finish taking the medication.

You can help prevent or lessen diarrhea by taking probiotics (separated from the Bactrim dose by 1-2 hours), eating a bland diet, and staying well-hydrated.

Mild diarrhea is caused by general gut flora disruption and is usually temporary. C. diff diarrhea is more severe, often accompanied by fever and intense cramping, and caused by a specific toxin-producing bacterium.

Yes, eating yogurt with live active cultures can be beneficial as it provides probiotics to help restore gut bacteria. For best results, consume it a few hours before or after your Bactrim dose.

Stick to bland, easy-to-digest foods like bananas, rice, applesauce, and toast. Avoid spicy, greasy, high-fiber, or high-sugar foods that can worsen symptoms.