Allopurinol (Zyloprim, Lopurin) is a generic prescription medication. It’s used to:

Allopurinol comes as an oral tablet. The drug also comes in injectable forms, but this article doesn’t cover them. As with other drugs, allopurinol can cause side effects.

Allopurinol is typically taken long term. However, the drug may be taken short term when it’s used with cancer treatments.

Read on to learn about potential common, mild, and serious side effects (also known as adverse effects). For a general overview of allopurinol, including details about its uses, refer to this article. Your doctor can also tell you more about allopurinol.

Allopurinol can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took allopurinol in clinical trials:

* This is a serious side effect of allopurinol. For details about this side effect, see the “Allopurinol: Side effect specifics” section below.

Mild side effects can occur with allopurinol treatment. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to allopurinol’s prescribing information.

Mild side effects that have been reported with allopurinol include:

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you develop a side effect while taking allopurinol and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see the “Allopurinol: Side effect specifics” section below.

Allopurinol may cause serious side effects. However, serious side effects with allopurinol aren’t common. The list below 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 allopurinol, 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 and their symptoms include:

* For more information about this side effect, see the “Allopurinol: Side effect specifics” section below.

Allopurinol may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

Do the different strengths of allopurinol, such as 100 mg and 300 mg, cause different side effects?

No, different strengths of allopurinol don’t cause different side effects. However, in general, the risk of side effects increases with a higher dose of a medication, including allopurinol. So, your risk of side effects may be higher if your doctor prescribes you a 300-mg dose compared to a 100-mg dose of allopurinol.

Talk with your doctor or pharmacist if you have additional questions about allopurinol strengths and dosages. You can also learn more about allopurinol dosages in this article.

Is weight gain a side effect of allopurinol?

No, it’s not likely you’ll experience weight gain as a side effect of allopurinol. Weight gain wasn’t seen in clinical trials of the drug.

However, doctors sometimes prescribe corticosteroids to treat a gout flare. Corticosteroids, such as prednisolone, are known to cause weight gain if taken long term. For this reason, doctors typically avoid prescribing corticosteroids long term to treat gout.

Talk with your doctor if you have questions or concerns about weight gain with allopurinol.

Can allopurinol cause long-term side effects?

Yes, it’s possible for allopurinol to cause long-term side effects. In allopurinol clinical trials, long-term side effects included:

Talk with your doctor or pharmacist if you have additional questions about allopurinol and long-term side effects.

* This is a serious side effect of allopurinol. To learn more, see the “Allopurinol: Side effect specifics” section below.

Does taking allopurinol with colchicine cause certain side effects?

No, taking allopurinol with colchicine (Colcrys) isn’t expected to cause certain side effects.

In fact, it’s common for doctors to prescribe allopurinol with colchicine for treating gout. This is especially the case when you first start taking allopurinol. This is because it can take several weeks for allopurinol to reach its full effect at treating gout. Prescribing colchicine helps lower your risk of gout flares while allopurinol takes time to work.

Talk with your doctor or pharmacist if you have additional questions about taking allopurinol and colchicine together.

Learn more about some of the side effects that allopurinol may cause. To find out how often side effects occurred in clinical trials, see the prescribing information for allopurinol.

Liver damage

Allopurinol treatment may cause liver damage but it rarely occurred in clinical trials of the drug. Liver damage is any change in the liver that reduces its ability to function.

Symptoms of liver damage include:

Your risk of liver damage with allopurinol is higher if you currently have a liver condition, such as hepatitis.

What you can do

Before or during treatment with allopurinol, your doctor may order blood tests to check your liver health. Liver function tests can help determine how well your liver is working. If you have an existing liver condition, they’ll likely order these tests more frequently during allopurinol treatment.

Tell your doctor if you develop any of the symptoms listed above while taking allopurinol. If you develop liver damage from the drug, your doctor will likely recommend you stop taking it. Typically, your body repairs the damage caused by allopurinol once your doctor stops the drug.

Note: A severe allergic reaction to allopurinol can also damage the liver. This damage may not go away, even if your doctor stops your treatment. For more information, see the “Skin rash” and “Allergic reaction” sections just below.

Muscle problems

Some people reported muscle problems in allopurinol clinical trials. Muscle problems included muscle pain and myopathy. With myopathy, your muscles work less effectively. Muscle problem side effects weren’t common.

Symptoms of myopathy include:

What you can do

If you develop muscle pain or symptoms of myopathy while taking allopurinol, tell your doctor. They’ll likely recommend stopping allopurinol treatment, which should ease your symptoms. Your doctor can also discuss other possible treatments for your condition that may be safer for you to take.

Skin rash

Taking allopurinol may cause a skin rash. In fact, a mild skin rash was one of the most common side effects reported in clinical trials.

Typically, a skin rash caused by allopurinol appears as flat, raised bumps on your skin. You may also notice a scale-like appearance to the rash. The bumps may also blister or peel.

However, skin rash while taking allopurinol can be serious and even life threatening, in rare cases.

Other symptoms that have been reported with a severe skin rash after taking allopurinol include:

  • fever
  • chills
  • joint pain and stiffness
  • jaundice
  • liver damage that may be permanent
  • blood cell problems, including thrombocytopenia

Your risk of developing a skin rash from taking allopurinol may be higher if you have kidney problems. Taking the antibiotics ampicillin or amoxicillin with allopurinol may also raise the risk of a skin rash.

What you can do

Immediately notify your doctor if you develop a skin rash or any of the symptoms listed above while taking allopurinol. Due to the risk of a skin rash to become serious, they’ll likely have you stop taking the drug.

Hair loss

Some people reported hair loss during clinical trials of allopurinol. Hair loss isn’t a common side effect with allopurinol.

With hair loss, symptoms don’t always include losing your hair completely. For example, you may notice your hair appears thinner than usual. Or you may notice you’re losing more hair than usual.

What you can do

If you experience hair loss while taking allopurinol, talk with your doctor about it. They’ll most likely recommend stopping treatment with the drug unless there’s another possible cause for your symptoms. They can then discuss other treatments for your condition that may be a better choice for you.

Note: Hair loss can be a side effect of other medications. To learn more, view this article.

Blood cell problems, including thrombocytopenia

Blood cell problems have been rarely reported in people taking allopurinol in clinical trials. These blood cell problems include thrombocytopenia (low platelet level) and leukopenia (low white blood cell level). Platelets help with blood clotting. White blood cells are part of your immune system and help fight off infections.

Symptoms aren’t common with these blood cell problems. In fact, you likely won’t notice symptoms if the decrease in blood cell levels is small. However, it’s possible for some symptoms to appear, especially in more serious cases. Some symptoms to watch for include:

  • small, round, dark skin spots, called petechiae
  • repeat infections or an infection that doesn’t go away
  • infection symptoms, such as fever, chills, fatigue, and sore throat

What you can do

Talk with your doctor right away if you notice any of the symptoms listed above. Blood cell conditions typically don’t cause symptoms until the problem becomes serious. So, it’s important for your doctor to see you as soon as possible. They can evaluate your symptoms and recommend the right treatment for you.

Depending on the severity of the blood cell problem, they may recommend that you stop taking allopurinol. They may be able to advise a different treatment option for you.

Allergic reaction

As with most drugs, allopurinol can cause an allergic reaction in some people. A mild allergic reaction, such as skin rash, was common compared to other side effects in the drug’s clinical trials. A more severe allergic reaction to the medication is rare.

Symptoms can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

In addition, drug-induced hypersensitivity syndrome has been reported with allopurinol. This is a rare but severe allergic reaction to the drug. In addition to the symptoms described above, allopurinol hypersensitivity syndrome may also cause:

The risk of allopurinol hypersensitivity syndrome is highest during your first few months of taking the drug. Other risk factors include having a certain gene called HLA-B*5801. This is a genetic marker that can increase your risk of serious hypersensitivity reactions to allopurinol. HLA-B*5801 is more common in people of Korean, Han Chinese, or Thai descent.

Note: Before prescribing allopurinol, your doctor may order a test to check if you have the HLA-B*5801 genetic marker. They may prescribe a drug other than allopurinol if the test is positive.

What you can do

If your symptoms are serious and you think you’re having a medical emergency, call 911 or your local emergency number.

For mild symptoms of an allergic reaction, call your doctor right away. They’ll determine whether you should continue taking the drug. They can also advise you on ways to ease your symptoms. If your doctor recommends, you can take over-the-counter allergy medication. To learn more about drugs for treating a mild allergic reaction, see this article.

Be sure to talk with your doctor about your health history before you take allopurinol. This drug may not be the right treatment option for you if you have certain medical conditions or other factors that affect your health. These are considered drug-condition or drug-factor interactions. The conditions and factors to consider include:

Kidney disease. Kidney disease, such as chronic kidney disease, increases the risk of side effects from allopurinol. The drug may also worsen your kidney disease. Due to these risks, your doctor will likely prescribe a lower allopurinol dose if you have kidney disease. Or they may recommend a different treatment. (For details about allopurinol dosages, see this article.)

Liver disease. Rarely, allopurinol can cause liver damage* as a side effect. Your risk of this side effect may be higher if you have an existing liver disease. It’s also possible that taking allopurinol could worsen your liver disease. So, if you have liver disease, talk with your doctor about it before taking allopurinol. If they recommend the drug, they’ll likely order liver function tests during treatment to monitor your liver health.

Allergic or severe reaction. If you’ve had an allergic reaction* to allopurinol or any of its ingredients, your doctor likely won’t prescribe allopurinol. Taking allopurinol could cause you to have another allergic reaction. You also should not take allopurinol if you’ve ever had a severe reaction, such as liver damage, to the medication. Ask your doctor what other medications may be better options for you.

* This is a serious side effect of allopurinol. To learn more, see the “Allopurinol: Side effect specifics” section above.

Alcohol with allopurinol

There’s no known interaction between allopurinol and drinking alcohol.

However, if you have gout or kidney stones, your doctor may suggest avoiding or reducing alcohol consumption. This is because drinking alcohol, particularly beer and whiskey, can increase uric acid levels. Drinking alcohol can also lead to dehydration, which is a risk factor for kidney stones.

If you have questions about drinking alcohol while taking allopurinol, talk with your doctor or pharmacist.

Pregnancy and breastfeeding while taking allopurinol

It’s not known if allopurinol is safe to take during pregnancy. Pregnant people weren’t included in the drug’s clinical trials.

The drug is rarely prescribed to people able to become pregnant. Most people taking allopurinol are older adults (age 65 years and over) not able to become pregnant.

It’s also not known if it’s safe to breastfeed while taking allopurinol. The drug is known to appear in breast milk. However, it’s not known what, if any, side effects this may cause in a child who’s breastfed.

If you’re pregnant, planning to become pregnant, or breastfeeding, talk with your doctor before starting allopurinol. They can provide more details and advise you about safe treatments for your condition.

If you’d like to learn more about allopurinol, talk with your doctor or pharmacist. They can help answer any questions you have about side effects from taking the drug. You can also ask them about Zyloprim, the brand-name version of allopurinol.

A generic drug and its brand-name version contain the same active ingredient, so they’re expected to have the same side effects. Referring to the following articles about allopurinol can provide you with additional information:

  • More information about allopurinol. For details about other aspects of allopurinol, refer to this article.
  • Cost. For information about cost and allopurinol, see this article.
  • A look at your condition. For details about your condition, see our list of gout articles.

Disclaimer: Medical News Today 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.