Does Allopurinol Cause Diarrhea? Understanding This Potential Side Effect

October 8, 2025 •

4 min read

Did you know that gastrointestinal issues, including nausea and diarrhea, are among the reported side effects of allopurinol? For patients taking this medication for gout or high uric acid, the question, "Does allopurinol cause diarrhea?" is a valid and important consideration for proper treatment management.

Quick Summary

Diarrhea is a known, though generally uncommon and mild, side effect of allopurinol. It can often be managed by taking the medication with food and staying properly hydrated.

Key Points

Diarrhea is a recognized side effect: Allopurinol can cause gastrointestinal issues, including diarrhea, though it is not a universal experience for patients.
Typically mild and uncommon: For the majority of users who experience it, allopurinol-related diarrhea is mild. Some reports indicate it affects less than 1% of patients.
Take medication with food to help: Taking allopurinol after a meal can significantly reduce the risk of stomach upset, including diarrhea and nausea.
Hydration is key: Staying well-hydrated is crucial, especially when experiencing diarrhea, to prevent dehydration and support overall health.
Consult a doctor for persistent symptoms: While mild diarrhea can be managed with simple steps, persistent, severe, or bloody diarrhea warrants immediate medical consultation.
Monitor for serious reactions: Diarrhea can sometimes accompany more severe adverse reactions, such as hypersensitivity syndrome, which requires urgent medical attention.

Understanding Diarrhea as an Allopurinol Side Effect

Allopurinol is a medication primarily used to treat gout and high uric acid levels by reducing the body's production of uric acid. While many people take allopurinol without experiencing significant side effects, gastrointestinal (GI) discomfort, including diarrhea, is a recognized adverse effect. The frequency of allopurinol-induced diarrhea varies among individuals, but it is generally considered a mild to uncommon side effect. One source notes that it is experienced by 1% or less of patients taking the drug, indicating it is not a widespread issue. Other GI effects that may accompany diarrhea include nausea, vomiting, and upset stomach.

Factors Influencing Gastrointestinal Side Effects

The likelihood and severity of GI side effects like diarrhea can be influenced by several factors, including the dosage, how the medication is taken, and individual patient sensitivities. Starting with a low dose and gradually increasing it, as recommended by healthcare providers, can help minimize side effects as the body adjusts. Patients with pre-existing kidney or liver issues may also be at a higher risk for adverse effects, making it crucial to discuss your full medical history with your doctor.

Managing Allopurinol-Related Diarrhea

For those who experience mild diarrhea or other stomach upset from allopurinol, several strategies can help manage the symptoms. It's often possible to reduce discomfort without needing to stop the medication, though you should always consult your doctor for personalized advice.

Take with food: Taking your allopurinol with or immediately after a meal or snack is one of the most effective ways to prevent stomach upset, including nausea and diarrhea.
Stay hydrated: Diarrhea can lead to dehydration, so it's vital to drink plenty of fluids throughout the day. Water is the best choice for staying hydrated and supporting overall kidney function.
Opt for bland foods: If you're experiencing stomach upset, sticking to a diet of bland foods can be helpful. This includes items like toast, rice, and bananas.
Avoid fatty and spicy foods: During bouts of diarrhea, it is best to avoid rich, greasy, or spicy foods that can further irritate the digestive system.
Smaller, more frequent meals: Eating smaller, more frequent meals instead of a few large ones can put less stress on your digestive system.

When to Contact a Doctor

While mild diarrhea from allopurinol is generally not a cause for alarm, certain symptoms warrant immediate medical attention. You should contact your healthcare provider if your diarrhea is:

Persistent or severe: If the diarrhea does not improve or worsens over time, a doctor's evaluation is necessary.
Watery or bloody: Bloody or excessively watery diarrhea is a sign of a more serious issue.
Accompanied by other severe symptoms: If you experience other side effects, such as a rash, fever, or signs of liver problems (e.g., jaundice, dark urine), stop taking the medication and seek emergency care.

Comparison of Allopurinol Side Effects

It's helpful to understand where diarrhea fits in the broader spectrum of allopurinol side effects. Here is a comparison of common versus more serious adverse reactions.


Side Effect Category	Common Examples	Frequency	Typical Management
Gastrointestinal	Diarrhea, Nausea, Vomiting, Upset stomach	Mild to Uncommon	Take with food, stay hydrated, bland diet
Skin	Rash (maculopapular, pruritic)	Common	Mild rash may be managed, but any rash warrants immediate medical consultation
Neurological	Drowsiness, Headache	Uncommon	Avoid driving until you know how the medication affects you
Hypersensitivity	Allergic reactions, Stevens-Johnson syndrome, DRESS syndrome	Rare but potentially life-threatening	Stop taking immediately and seek emergency medical care
Liver/Kidney	Increased liver enzymes, liver damage, kidney injury	Rare; Higher risk with pre-existing conditions	Regular monitoring; requires immediate medical attention if symptoms arise
Other	Gout flares (initial treatment), Bone marrow suppression	Initial flares are common; bone marrow issues are rare but serious	flares often managed with other meds; monitor blood counts for bone marrow effects

Conclusion

Diarrhea is a recognized, though not common, side effect of allopurinol. For most patients, this gastrointestinal discomfort is mild and can be effectively managed by simple dietary changes and lifestyle adjustments, such as taking the medication with food and staying hydrated. It is crucial to monitor your symptoms and communicate with your healthcare provider. While allopurinol is a safe and effective treatment for many, being aware of potential side effects and knowing how to respond is a key part of successful long-term management of conditions like gout and high uric acid. In the rare instance of severe or persistent GI symptoms, or if accompanied by signs of a more serious reaction, prompt medical attention is essential.

For More Information

MedlinePlus Allopurinol Information: For detailed drug information, including dosage and side effects, consult this reputable source.

Frequently Asked Questions

No, diarrhea from allopurinol is not very common. Some sources indicate it is experienced by 1% or less of patients. For those who do get it, it is usually a mild, manageable side effect.

To help prevent or lessen gastrointestinal side effects like diarrhea, you should take your allopurinol with or after a meal. You should also stay well-hydrated throughout the day and avoid greasy, rich, or spicy foods.

For mild diarrhea, you should not stop taking allopurinol unless advised by a healthcare provider. Often, managing the side effect with food and hydration is enough. However, you should contact your doctor if the diarrhea is severe, bloody, or persistent.

Yes, other GI issues are also common. Nausea, upset stomach, and vomiting are frequently reported alongside diarrhea. Taking the medication with food can help mitigate these symptoms as well.

Yes, starting with a lower dose and slowly increasing it under a doctor's supervision can help reduce the initial side effects, including gastrointestinal discomfort. Higher doses may increase the risk of side effects.

If your diarrhea is severe, persistent, or bloody, you should contact a healthcare professional immediately. These symptoms could indicate a more serious issue and require medical evaluation.

You should not take any other medications, including over-the-counter drugs like anti-diarrheals, without consulting your doctor or pharmacist first. They can advise you on safe and appropriate treatment options.

Most mild side effects from allopurinol, including diarrhea, are temporary and may improve as your body adjusts to the medication. If they persist for more than a few weeks, it's best to speak with your doctor.