Key takeaways

  • More common side effects associated with allopurinol include diarrhea, nausea, and elevated liver enzymes.
  • Allopurinol can be used short term or long term, depending on the condition it’s being used to treat.
  • Serious side effects that have been reported with allopurinol include gout episodes, blood vessel inflammation and damage, decreased levels of red and white blood cells, and more.

Allopurinol is generic drug used to treat conditions related to high uric acid levels adults and some children, including:

Allopurinol comes as an oral tablet (a tablet that you swallow). It also comes in injectable forms, but this article does not cover those forms.

Keep reading to learn about the common, mild, and serious side effects allopurinol can cause. To learn more about allopurinol, including its uses, dosage, and cost, read this allopurinol overview.

Allopurinol can cause certain side effects, some more common than others. These side effects may be temporary, lasting a few days to weeks. Talk with your doctor if side effects do not go away, get worse, or become too difficult to tolerate.

Allopurinol’s commonly reported side effects include:

  • diarrhea
  • nausea
  • liver enzyme increase, which in rare cases can be a sign of liver problems

Mild side effects have been reported with allopurinol’. These include:

In most cases, these side effects should be temporary, and some may be easily managed. But if you have symptoms that are ongoing or bothersome, talk with your doctor or pharmacist. Do not stop taking allopurinol unless your doctor recommends it.

Allopurinol may cause mild side effects other than those listed here. See the drug’s prescribing information for details.

Allopurinol may cause serious side effects. The following list may not include all possible serious side effects of the drug. For more information, you can refer to allopurinol’s prescribing information.

If you develop serious side effects while taking X drug, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Serious side effects that have been reported include:

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Sharing your experience helps make medication safer for everyone by giving doctors and researchers more information about how the drug works in real life. If you develop a side effect while taking allopurinol and want to tell the FDA about it, visit MedWatch or call 800-FDA-1088.

Allergic reaction

For some people, allopurinol can cause an allergic reaction.

This side effect was reported in the drug’s studies.

In general, symptoms of an allergic reaction can be mild or serious.

What might help
If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms and can determine whether you should keep taking allopurinol drug.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to allopurinol, they may have you switch to a different treatment.

Here are answers to some commonly asked questions about allopurinol’’s side effects.

Is there a lower risk of adverse effects from the 100-mg dose of allopurinol compared with the 300-mg dose?

It depends. Your doctor will usually start you on a low dose of allopurinol and increase it slowly. If you have side effects with an allopurinol starting dosage of 100 milligrams (mg) once daily, your doctor likely will not increase your dosage. Similarly, your doctor will likely not increase your dosage if you have side effects after an increase to 200 mg or higher once daily.

If you have certain medical conditions, you may have a higher risk of side effects from allopurinol. If you have questions about allopurinol’s side effects, talk with your doctor or pharmacist.

Does allopurinol cause any long-term side effects?

Yes, but rarely. Most of the time, allopurinol does not cause long-term side effects.

But short-term allopurinol side effects could have long-term effects if left untreated. For example, liver or blood vessel damage could lead to other long-term health conditions.

Certain side effects, such as decreased bone marrow function, may occur anywhere from 6 weeks to 6 years after starting allopurinol treatment. This side effect often happened in people who also took other drugs that could cause decreased bone marrow function.

To find out about your risk of long-term side effects from taking allopurinol, talk with your doctor.

Does allopurinol have a side effect of high blood pressure?

No. Studies of allopurinol did not report high blood pressure as a side effect.

If you notice or suspect changes in your blood pressure, such as high blood pressure, while taking allopurinol, talk with your doctor. They can evaluate you and suggest was to manage the condition, if necessary.

There may be things you can do to help make certain allopurinol side effects more manageable. If you have ongoing, worsening, or bothersome side effects, talk with your doctor or pharmacist. They can suggest tips for managing them or recommend other available treatment options for your condition.

Liver-related side effects

Liver damage was reported as a rare side effect in studies of allopurinol. Other liver-related side effects that allopurinol can cause include:

  • enlarged liver
  • death of liver tissue
  • inflammation (swelling and damage) in the liver

Symptoms of liver damage include:

What might help

While you’re taking allopurinol, your doctor will monitor you for symptoms of liver damage. They’ll also have you get blood tests to keep track of your liver function.

If you have increased levels of liver enzymes, it can be a sign that allopurinol is affecting your liver. But your doctor likely won’t change your allopurinol treatment unless you also have symptoms of liver problems or damage.

If you develop liver damage or other liver-related side effects that cause symptoms, your doctor will likely have you stop taking allopurinol. This will usually relieve symptoms of liver-related side effects.

Hair loss

Allopurinol can cause hair loss, though this side effect was rare in studies of the drug. If you notice thinning or you develop bald patches after starting allopurinol treatment, it may be related to the drug.

Other symptoms of hair loss are:

  • a widening part
  • loose hair in your brush or comb
  • more hair than usual in the shower drain

What might help

There are ways to prevent hair loss and to help hair regrow. These include:

  • taking prescription medications, such as finasteride (Propecia, Proscar)
  • using over-the-counter treatments, such as minoxidil foam (Rogaine)
  • treating the underlying condition, if any, that caused hair loss
  • having hair transplant surgery

Before taking allopurinol, discuss your health history with your doctor. Allopurinol may not be right for you if you have certain medical conditions or other factors affecting your health. Be sure to talk with your doctor if any of the following apply to you:

  • serious reaction when previously taking allopurinol, such as Steven’s-Johnson syndrome
  • kidney problems
  • liver problems
  • previous allergic reaction
  • pregnancy
  • breastfeeding

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.