Can Macrobid Cause Diarrhea? Understanding the Side Effect

October 12, 2025 •

3 min read

Macrobid, also known by its generic name nitrofurantoin, is an antibiotic that commonly causes gastrointestinal side effects. Diarrhea is among the most reported of these issues, and understanding why it occurs is key to managing it effectively during your treatment.

Quick Summary

Macrobid (nitrofurantoin) can cause diarrhea by altering the normal balance of gut bacteria. This is often a mild side effect, but patients should recognize signs of more severe infections like C. difficile.

Key Points

Antibiotic-Associated Diarrhea: Macrobid can cause diarrhea by disrupting the normal bacterial balance in your gut.
Take With Food: Always take Macrobid with food or milk to minimize stomach upset and nausea, which can reduce the likelihood of diarrhea.
Stay Hydrated: It is crucial to drink plenty of fluids, especially if experiencing diarrhea, to prevent dehydration.
Probiotics Can Help: Taking probiotic supplements may help restore healthy gut flora, but they should be taken a few hours apart from the antibiotic dose.
Watch for Severe Symptoms: Call a doctor immediately if you experience severe watery or bloody diarrhea, fever, or stomach cramps, as this could indicate a serious infection.
Low C. diff Risk: Compared to many other antibiotics, Macrobid has a lower risk of causing a severe Clostridioides difficile infection, though the risk still exists.
Complete the Course: Finish the entire prescribed course of Macrobid to effectively treat your UTI and prevent the development of antibiotic resistance.

The Connection: Why Macrobid Causes Diarrhea

Macrobid, a powerful antibiotic used to treat urinary tract infections (UTIs), works by killing bacteria in the urinary tract. Its active ingredient, nitrofurantoin, is reduced by bacterial flavoproteins into reactive intermediates that damage the bacteria's vital processes, such as protein and DNA synthesis. However, this antibacterial action is not always selective and can disrupt the natural, healthy balance of microorganisms in your gut, leading to diarrhea.

Disrupting Gut Flora

Your digestive tract hosts trillions of beneficial bacteria that aid digestion and keep harmful bacteria in check. When you take an antibiotic like Macrobid, it can inadvertently kill off some of this 'good' bacteria, upsetting the delicate microbial ecosystem. This imbalance can lead to symptoms like cramping, bloating, and diarrhea. While this is a common side effect with many antibiotics, modern formulations like Macrobid's macrocrystals are designed to be absorbed more slowly, which can reduce the frequency of gastrointestinal issues compared to older versions.

Mild vs. Severe Diarrhea

It is important to differentiate between mild, antibiotic-associated diarrhea and more severe conditions. Mild diarrhea is a temporary annoyance that often resolves once the medication course is finished. However, in rare cases, this disruption can lead to an overgrowth of a specific bacterium called Clostridioides difficile (C. diff). This can cause severe, watery, or bloody diarrhea, abdominal cramps, and fever, sometimes occurring up to two months after completing the antibiotic treatment.

Managing Diarrhea While Taking Macrobid

If you experience mild diarrhea, several strategies can help manage the symptoms and promote a healthier gut environment during treatment:

Take with food: Taking Macrobid with food or milk can significantly reduce stomach upset, including nausea and diarrhea.
Stay hydrated: Drink plenty of fluids, especially water and electrolyte-rich drinks like broths or sports beverages, to prevent dehydration.
Consider probiotics: Probiotics may help replenish beneficial gut bacteria. However, it is important to take them at least two hours before or after your antibiotic dose to prevent the antibiotic from killing the good bacteria in the supplement.
Follow the BRAT diet: The BRAT diet (bananas, rice, applesauce, toast) consists of low-fiber, bland foods that can help bind your stools and ease digestive upset.
Avoid certain foods: Steer clear of rich, spicy, or fatty foods that can further irritate the stomach during your treatment period.

Comparing Macrobid's Side Effects to Other Antibiotics

Macrobid is often considered to have a favorable side effect profile compared to other UTI antibiotics, especially regarding serious issues. Below is a comparison of gastrointestinal side effects for common UTI treatments:


Antibiotic	Diarrhea	Nausea/Vomiting	Other Key Side Effects
Macrobid (Nitrofurantoin)	Uncommon	Common	Urine discoloration, headache, lung reactions (rare)
Ciprofloxacin (Cipro)	Common	Common	Tendonitis, tendon rupture, nerve damage (boxed warning)
Bactrim (Trimethoprim/Sulfa)	Common	Common	Skin rashes, Stevens-Johnson syndrome (rare)

When to Seek Medical Attention

While mild diarrhea is manageable, certain symptoms warrant immediate medical attention to rule out a more serious condition like C. difficile colitis:

Severe, watery, or bloody diarrhea
Fever
Severe stomach pain or cramps
Diarrhea that continues even after you have finished taking Macrobid

If you experience any of these signs, contact your healthcare provider right away. Do not attempt to treat severe diarrhea with over-the-counter anti-diarrheal medications without a doctor's guidance.

Conclusion

Yes, Macrobid can cause diarrhea as a side effect, like most antibiotics, due to its effect on gut bacteria. For most people, this side effect is mild and can be managed effectively with simple dietary adjustments and by taking the medication with food. Staying hydrated and considering a probiotic may also be beneficial. However, awareness of the more serious signs of a C. difficile infection is crucial. Always complete the full course of your Macrobid prescription as directed by your doctor, even if you start to feel better, and contact a healthcare professional if you experience severe or persistent symptoms. The overall benefits of treating a UTI with Macrobid generally outweigh the manageable risks of common gastrointestinal side effects, especially when compared to broader-spectrum antibiotics.

Additional Resources

For more detailed information on antibiotic-associated diarrhea, consult authoritative sources such as the Mayo Clinic's overview of the topic.

Frequently Asked Questions

Diarrhea is a relatively common gastrointestinal side effect, though it is less frequent than nausea or vomiting. In clinical trials of Macrobid, abdominal pain and diarrhea were less common gastrointestinal reactions than nausea and vomiting.

Yes, Macrobid can cause your urine to turn a harmless dark yellow or brown color. This is a normal side effect that indicates the medication is working and will resolve after you stop taking it.

You should consult a healthcare provider before taking any anti-diarrheal medication, such as loperamide. Some of these medications should not be used if a C. difficile infection is suspected, as they can worsen the condition.

Clostridioides difficile (C. diff) is a bacteria that can overgrow in the gut when antibiotics disturb the normal flora, causing severe diarrhea and potentially fatal colitis. Macrobid, like most antibiotics, carries a risk, though it is considered a low-risk antibiotic for C. diff.

In most mild cases, the diarrhea subsides shortly after completing the course of medication. If you have severe diarrhea, or if it continues for an extended period, contact your doctor.

Yes, taking probiotics may help by introducing beneficial bacteria back into the gut, but they should be taken at least two hours before or after your antibiotic dose to prevent the antibiotic from killing the probiotic bacteria.

The BRAT diet (bananas, rice, applesauce, toast) can be helpful. You should also focus on staying hydrated with water and electrolyte-rich drinks and avoid fatty, spicy, or rich foods.