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Generic name: allopurinol (oral/injection) [ AL-oh-PURE-i-nol ]
Brand names: Zyloprim, Lopurin, Aloprim
Dosage forms: intravenous powder for injection (500 mg), oral tablet (100 mg; 200 mg; 300 mg)
Drug classes: Antigout agents, Antihyperuricemic agents

Medically reviewed by Sanjai Sinha, MD. Last updated on Apr 4, 2023.

What is allopurinol?

Allopurinol belongs to a class of medications called xanthine oxidase inhibitors. It works by reducing the production of uric acid in the body. High levels of uric acid may cause gout attacks or kidney stones.

Allopurinol is used to treat gout (a type of arthritis in which uric acid, a naturally occurring substance in the body, builds up in the joints and causes sudden attacks of redness, swelling, pain, and heat in one or more joints). Allopurinol is used to prevent gout attacks, not to treat them once they occur.

Allopurinol is also used to treat high levels of uric acid that builds up in the blood as tumors break down in people with certain types of cancer who are being treated with chemotherapy medications. It is also used to treat kidney stones that have come back in people who have high levels of uric acid in their urine.


You should not use this medicine if you have ever had an allergic reaction to allopurinol.

Allopurinol can lower blood cells that help your body fight infections. This can make it easier for you to bleed from an injury or get sick from being around others who are ill. Your blood may need to be tested often. Visit your doctor regularly.

In rare cases, allopurinol may cause a severe allergic reaction. Stop taking this medicine and call your doctor right away if you have painful urination, blood in your urine, burning in your eyes, swelling in your face or throat, skin redness or a rash that spreads and causes blistering and peeling.

Avoid drinking alcohol. It can make your condition worse. Allopurinol may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert.

Before taking this medicine

You should not use allopurinol if you are allergic to it.

To make sure this medicine is safe for you, tell your doctor if you have ever had:

  • diabetes;

  • congestive heart failure;

  • high blood pressure;

  • if you are receiving chemotherapy;

  • if you have a gene variation called HLA-B*58:01 allele (your doctor can test you for this);

  • liver disease; or

  • kidney disease.

Allopurinol may harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.

Do not breastfeed while using this medicine, and for at least 1 week after your last dose.

How should I use allopurinol?

Take allopurinol exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose.

Take the tablets with a full glass of water. To reduce your risk of kidney stones, drink 8 to 10 full glasses of fluid every day, unless your doctor tells you otherwise.

Take with food if allopurinol tablets upsets your stomach.

Allopurinol injection is injected into a vein by a healthcare provider. The injection is usually only used if you are unable to take medicine by mouth.

You may need frequent medical tests while using this medicine, even if you have no symptoms.

Your kidney and liver function may also need to be tested. Your doctor may change your dose if your kidney function changes.

You may have gout attacks when you first start taking allopurinol tablets. Your doctor may recommend another gout medication to take with allopurinol. Keep taking the medicine as directed.

Your symptoms may not improve for up to 2 to 6 weeks. Call your doctor if your symptoms do not improve after 6 weeks.

You may need to follow a special diet to help prevent kidney stones. Follow all instructions of your doctor or dietitian. Learn about the foods you should eat or avoid.

Store at room temperature away from moisture and heat.

What happens if I miss a dose?

Take allopurinol as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

Call your doctor for instructions if you miss an appointment for your allopurinol injection.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while using allopurinol?

Avoid driving or hazardous activity until you know how allopurinol will affect you. Your reactions could be impaired.

Avoid drinking alcohol.

Allopurinol side effects

Get emergency medical help if you have signs of an allergic reaction to allopurinol (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include skin rash, fever, swollen glands, muscle aches, severe weakness, unusual bruising, or yellowing of your skin or eyes.

Allopurinol may cause serious side effects. Stop using this medicine and call your doctor at once if you have:

  • any skin rash, no matter how mild;

  • painful urination, blood in the urine;

  • inflammation of your blood vessels - numbness or tingling, skin rash, fever, headache, body aches, night sweats, weight loss, feeling or weak or tired;

  • signs of infection - fever, chills, sore throat, body aches, unusual tiredness, loss of appetite, bruising or bleeding; or

  • liver problems - loss of appetite, weight loss, stomach pain (upper right side), itching, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Common allopurinol side effects may include:

  • an increase in gout attacks when you first start taking this medicine;

  • rash;

  • drowsiness;

  • abnormal liver function tests;

  • nausea, vomiting, diarrhea; or

  • kidney problems - swelling, urinating less, feeling tired or short of breath.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect allopurinol?

Tell your doctor about all your other medicines, especially:

This list is not complete. Other drugs may interact with allopurinol, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use allopurinol only for the for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.