Does nitrofurantoin cause diarrhea? A look at gastrointestinal side effects

October 12, 2025 •

4 min read

Approximately 23–34% of patients taking nitrofurantoin (Macrobid) experience gastrointestinal side effects, including nausea, vomiting, and loss of appetite. While often not the most common symptom, does nitrofurantoin cause diarrhea? The answer is yes, and it is a known adverse reaction, though usually less prevalent than other stomach issues.

Quick Summary

Nitrofurantoin, a common antibiotic for UTIs, can cause diarrhea due to its impact on gut bacteria. Mild cases can be managed with supportive care, while severe, persistent, or bloody diarrhea may indicate a serious condition like C. difficile and requires immediate medical attention. Taking the medication with food can help minimize stomach upset.

Key Points

Diarrhea is a possible side effect of nitrofurantoin: While less common than nausea, it can occur and is caused by the antibiotic disrupting gut bacteria.
Taking with food helps reduce side effects: To minimize stomach upset, including the risk of diarrhea, it is recommended to take nitrofurantoin with food or milk.
Mild diarrhea can be managed at home: Maintaining hydration, following the BRAT diet, and considering probiotics (with a doctor's approval) are effective strategies for mild cases.
Severe diarrhea requires immediate medical attention: Watery or bloody stools, persistent diarrhea, severe stomach cramps, or fever can indicate a serious condition like C. difficile and should be reported to a doctor immediately.
Do not use anti-diarrheal medication without a doctor's consent: Anti-diarrheal medicines can worsen severe infections and should be avoided unless specifically directed by a healthcare provider.
Macrobid formulation may reduce nausea: The macrocrystalline (Macrobid) form of nitrofurantoin is designed to be absorbed more slowly, which can be easier on the stomach compared to other formulations.

Understanding Nitrofurantoin's Role

Nitrofurantoin is an antibiotic specifically prescribed for the treatment and prevention of uncomplicated lower urinary tract infections (UTIs). Unlike systemic antibiotics that travel throughout the body, nitrofurantoin is quickly filtered out of the blood and concentrated in the urine, allowing it to target bacteria directly at the site of infection in the bladder. This pharmacokinetic property also means it has a relatively low impact on the wider body, contributing to its generally favorable safety profile compared to some alternative antibiotics. The medication works by damaging bacterial DNA, proteins, and cell wall synthesis, making it difficult for bacteria to develop resistance.

How Nitrofurantoin Can Cause Diarrhea

Diarrhea is a recognized side effect of nitrofurantoin, though it is less common than other gastrointestinal symptoms like nausea and vomiting. The mechanism is a common one for most antibiotics: the medication can disrupt the delicate balance of the gut's natural microbiota, or 'gut flora'. This disruption can lead to an overgrowth of harmful bacteria, causing inflammation and resulting in diarrhea. While nitrofurantoin is designed to have lower systemic concentrations and thus less impact on gut flora than some other antibiotics, the risk of mild diarrhea and more serious infections still exists.

Another formulation difference can affect GI side effects. Macrobid, the macrocrystalline formulation, is absorbed more slowly than other forms of nitrofurantoin, which can help reduce stomach upset and nausea. However, diarrhea is a possible reaction with any formulation.

Gastrointestinal Side Effects: A Closer Look

While diarrhea can occur, the most common gastrointestinal side effects associated with nitrofurantoin are nausea and vomiting. Taking the medication with food can help mitigate these symptoms, as it can slow absorption and make the drug gentler on the stomach.

Recognizing and Managing Mild Diarrhea

In most cases, any diarrhea experienced while taking nitrofurantoin is mild and temporary, resolving on its own once the course of treatment is finished. Proper management can help ease discomfort and prevent dehydration.

Tips for managing mild antibiotic-associated diarrhea:

Stay Hydrated: Drink plenty of fluids, including water, broth, and electrolyte-rich sports drinks, to replace lost fluids and prevent dehydration.
Follow the BRAT Diet: Stick to bland, easily digestible foods like Bananas, Rice, Applesauce, and Toast to help bind your stool.
Eat Smaller, More Frequent Meals: If you're experiencing a loss of appetite along with diarrhea, smaller meals can be easier to tolerate.
Consider Probiotics: Taking a probiotic supplement or consuming foods with live cultures, such as yogurt, can help restore healthy gut bacteria. However, it is advisable to discuss this with your doctor first.
Do Not Use Anti-Diarrheal Medications: Unless specifically instructed by a doctor, avoid using over-the-counter anti-diarrheal medicines. These can mask symptoms of a more serious infection and sometimes worsen the condition.

When Diarrhea Becomes a Serious Concern

Although rare, some forms of antibiotic-associated diarrhea can be serious and require immediate medical attention. A key risk is Clostridioides difficile (C. diff) colitis, an infection that can occur during or even months after antibiotic treatment has concluded.

Call your doctor immediately if you experience:

Diarrhea that is watery or bloody.
Diarrhea that is persistent and does not stop.
Severe stomach cramps or abdominal pain.
Fever that begins during or after your antibiotic treatment.
Blood or mucus in your stool.

Nitrofurantoin vs. Other Common UTI Antibiotics

Different antibiotics used for UTIs carry varying risks and side effect profiles. Here's a comparison of common GI-related effects:


Antibiotic	Primary Target Area	Common GI Side Effects	C. difficile Risk	Other notable side effects
Nitrofurantoin	Urinary tract	Nausea, vomiting, mild diarrhea	Low to moderate (still possible)	Headache, dizziness, dark urine
Trimethoprim-sulfamethoxazole (Bactrim)	Systemic	Nausea, vomiting, diarrhea	Moderate to high	Allergic skin reactions, photosensitivity
Ciprofloxacin (Cipro)	Systemic	Nausea, vomiting, diarrhea, abdominal pain	High	Tendonitis, nerve damage, photosensitivity

Note: This table provides a general comparison. Individual reactions to any medication can vary, and this information should not replace medical advice.

Preventing Diarrhea While Taking Nitrofurantoin

Preventing diarrhea starts with proper medication use. Always take the full prescribed course of antibiotics, even if you feel better, to ensure the infection is completely eradicated. Stopping prematurely can increase the risk of a resistant infection returning, which can require more powerful antibiotics with potentially greater side effects. Taking nitrofurantoin with food or milk is the most straightforward and effective method for reducing common stomach upset, including the risk of diarrhea. Maintaining good hydration is crucial throughout the treatment. If you are prone to antibiotic-associated diarrhea, your doctor may suggest starting a probiotic during your antibiotic course, but always consult with them first.

Conclusion

Yes, nitrofurantoin can cause diarrhea, though it is typically a less common side effect than nausea and vomiting. It results from the antibiotic's effect on the natural balance of gut bacteria, a risk common to all antibiotic treatments. For mild cases, supportive measures like dietary adjustments and hydration are usually sufficient. However, any indication of severe, persistent, or bloody diarrhea warrants immediate medical consultation due to the risk of more serious conditions like C. difficile colitis. By understanding the potential side effects and knowing how to respond appropriately, patients can safely complete their treatment for a urinary tract infection.

This article is for informational purposes only and should not be considered a substitute for professional medical advice. Always consult your healthcare provider with any questions about your medication and potential side effects.

For more information on antibiotic-associated diarrhea and C. difficile, visit the U.S. Centers for Disease Control and Prevention (CDC) website.

Frequently Asked Questions

While gastrointestinal issues are common, diarrhea is less frequent than other side effects like nausea and vomiting. The FDA drug label mentions diarrhea as a less common adverse reaction.

Antibiotics disrupt the natural balance of microorganisms (gut flora) in your digestive system by killing off healthy bacteria along with the harmful ones. This imbalance can lead to an overgrowth of other bacteria and result in diarrhea.

Yes, taking a probiotic supplement or eating yogurt with live cultures may help restore healthy gut bacteria and reduce the risk or severity of antibiotic-associated diarrhea. Always consult your doctor before starting any supplements.

No, you should not stop your prescribed course of antibiotics without consulting your doctor, even if your symptoms improve or you experience side effects like mild diarrhea. Stopping early can lead to a return of the infection.

You should contact your doctor immediately if you experience severe, watery, or bloody diarrhea; severe abdominal cramping; or a fever. These could be signs of a serious intestinal infection.

Taking nitrofurantoin with food is recommended to reduce stomach upset, which can help mitigate the risk of gastrointestinal issues, including diarrhea. It also improves absorption.

Do not take any anti-diarrheal medicine without first checking with your doctor. These medications can sometimes make a more serious infection worse or prolong the condition, and your doctor needs to assess the cause of your diarrhea.

Gastrointestinal side effects typically occur during the first week of treatment. However, severe diarrhea from a C. difficile infection can emerge during treatment or even weeks to months after the antibiotic course is finished.