Allopurinol

Medically Reviewed By University of Illinois Chicago Drug Information Group

Allopurinol at a glance

Key highlights to know about allopurinol are:

  • Allopurinol is used to prevent gout attacks, reduce the amount of uric acid levels in the blood caused by certain medications used to treat cancer, and prevent frequent kidney stones.
  • Allopurinol is taken by mouth one or two times a day after a meal. Drink plenty of water or other fluids as directed by your doctor.
  • Drinking alcohol may reduce how well allopurinol works. Consult with your doctor and pharmacist to learn if it is safe to drink alcohol while taking allopurinol. Loss of appetite and unexpected weight loss may occur while taking allopurinol. This is considered a serious side effect. Contact your doctor immediately if you notice these changes.
  • Allopurinol is considered a low-cost drug (defined in this article as costing less than $30/month).
  • Allopurinol is available as a tablet as a generic and brand-name (Zyloprim) drug.

Important safety warnings for allopurinol

Users of allopurinol should be aware of these safety warnings:

  • Drowsiness warning: Allopurinol can cause drowsiness. Be sure to take caution when driving or doing other tasks that require you to be alert.
  • Drug interaction warning: If you take mercaptopurine or azathioprine, the dose of these medications will have to be changed when you start taking allopurinol. Be sure to let your doctor know about all medications you are taking.
  • Liver injury warning: Allopurinol may affect how well your liver works. If you already have reduced liver function or if you experience weight loss, reduced appetite, or severe itching while taking allopurinol, let your doctor know. You may have to get blood tests to monitor how your liver is working.
  • Serious allergic reaction and reduced kidney function warning: The chance of an allergic reaction to allopurinol may be higher if you have reduced kidney function and are taking a thiazide diuretic. Be sure to let your doctor know of all your past medical conditions and other medications you take before taking allopurinol.
  • Skin rash warning: Allopurinol may cause an allergic reaction that can start as a skin rash. The rash can lead to more serious skin reactions. If you develop a skin rash, see your doctor right away and stop taking allopurinol.

Talk with your doctor about these warnings in the context of your individual treatment plan and medical history.

What allopurinol treats

This medication is used to:

  • Prevent gout attacks
  • Reduce high uric acid levels caused by medications used to treat cancer
  • Prevent frequent kidney stones

Doctors sometimes prescribe medications for different uses. Ask your doctor or pharmacist for information about other uses of this medication.

How it works

Allopurinol is a prescription drug that belongs to a class of medications called xanthine oxidase inhibitors. It works by reducing the amount of uric acid made by the body. High uric acid in the body can cause gout attacks, kidney stones, and kidney injury.

Allopurinol takes time to reduce the amount of uric acid in the body, so its benefit may not be felt right away. In fact, when you start allopurinol, the number of gout attacks may increase, but over time, allopurinol should prevent or reduce the number of gout attacks you have. Your doctor may prescribe you another medication to manage gout attacks if they occur when you first start taking allopurinol. Do not stop taking allopurinol even if you feel well. Discuss any concerns of continuing allopurinol with your doctor.

Allopurinol is available as a tablet. It is available as a generic or brand-name (Zyloprim) product.

Side effects of allopurinol

Allopurinol side effects are possible and may go away with continued use. Serious side effects are rare.

Common side effects

The more common side effects that occur with allopurinol include:

  • Diarrhea
  • Drowsiness
  • Upset stomach

Serious side effects

Call your doctor right away if you have serious side effects. Seek emergency care (call 911) if you experience life-threatening symptoms, such as difficulty breathing; chest pain; loss of consciousness; sudden vision changes; or swelling of the face, mouth, tongue or throat.

Serious side effects and their symptoms can include the following:

  • Bone marrow depression. Symptoms include:
    • Fever
    • Sore throat
    • Chills
    • Signs of infection
  • Blood in the urine
  • Irritation in the eyes
  • Kidney injury
  • Liver injury. Symptoms include:
    • Itching
    • Weight loss
    • Loss of appetite
  • Painful urination
  • Skin rash
  • Swelling of the lips or mouth.

Other side effects are possible. Talk to your doctor or pharmacist if you have any side effect that bothers you or that does not go away.

Costs of allopurinol

Without insurance, allopurinol is typically a low-cost drug (defined in this article as costing less than $30/month). You can check the out-of-pocket cash pay price for allopurinol on prescription drug discount websites.

With insurance, prices can vary considerably. Individual health plans may have preferred drugs with better pricing. If the price of allopurinol on your health plan is too expensive, ask your doctor or pharmacist if there is an equivalent drug you can substitute.  

How allopurinol may interact with other medicines

Allopurinol may interact with other prescription and over-the-counter medications, vitamins, or herbal supplements you may be taking. To help avoid harmful interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbal supplements you are taking. To find out how this drug might interact with something else you are taking, talk to your doctor or pharmacist.

This is not a complete list of drugs that may interact with allopurinol. However, examples of drugs that may interact with allopurinol include:

Penicillins

If you take allopurinol with certain penicillin antibiotics, this may increase the chance of an allergic reaction to the penicillin antibiotic, including: 

  • Amoxicillin
  • Ampicillin

Warfarin

If you take allopurinol with warfarin—an anticoagulant—this may increase the risk of bleeding with warfarin. Your doctor will need to monitor the effects of warfarin when you start or stop taking allopurinol.

Cancer Chemotherapy Drugs

If you take allopurinol with certain chemotherapy drugs, this may increase the chance of bone marrow suppression. Your doctor will need to monitor your blood counts closely with: 

  • Cyclophosphamide

If you take allopurinol with mercaptopurine, the dose of mercaptopurine will need to be reduced.

Immunosuppressants

If you take allopurinol with certain immunosuppressant drugs, allopurinol can increase the levels of these drugs in your body. The dose of these immunosuppressants may need to be adjusted (specifically, azathioprine) or closely monitored:

  • Azathioprine
  • Cyclosporine

Hydrochlorothiazide

If you take allopurinol with hydrochlorothiazide (diuretic), there may be a higher chance of an allergic reaction to allopurinol. 

Disclaimer: Since drugs interact differently in each person, this information is not guaranteed to include all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbal supplements, and over-the-counter drugs you are taking.

Other allopurinol alerts

This drug comes with additional alerts:

Dietary intake

If you are taking allopurinol to prevent gout or frequent kidney stones, ask your doctor about any recommended changes in your diet. A diet low in animal protein, salt, and refined sugar may be recommended by your doctor. Certain foods can also help reduce the chance of kidney stones.

Fluid intake

While taking allopurinol, drink at least eight glasses of water or other fluids each day unless your doctor advises you otherwise. This helps prevent the buildup of uric acid and kidney stones.

Impaired kidney function

The dose of allopurinol will be lower if the function of your kidneys is reduced.

Acute gout attacks

When first starting allopurinol, you may have an increase in the number of gout attacks. This can be managed with other gout medications. Your doctor should give you information on how to manage these attacks if they occur. Do not stop taking allopurinol if this occurs. The full effect of allopurinol happens weeks after you take it regularly as prescribed.

Call your doctor right away if you have serious side effects. Seek emergency care (call 911) if you experience life-threatening symptoms, such as difficulty breathing; chest pain; loss of consciousness; sudden vision changes; or swelling of the face, mouth, tongue or throat.

For pregnant and breastfeeding women

Can I take allopurinol when pregnant?

It is not known if taking allopurinol during pregnancy will harm your unborn baby. If you plan on becoming pregnant, talk with your healthcare provider.

Can I take allopurinol when breastfeeding?

Allopurinol passes into breast milk. However, the effects of allopurinol on the breast-fed infant are unknown. Talk to your doctor if you breastfeed your child about precautions you need to take.

How and when to take allopurinol

Allopurinol is a medication taken by mouth after a meal. Your doctor will determine the amount you need to take. The medication dose may be low when you first start it. Your doctor may slowly increase the dose depending on how you do and how much you need. You may start taking allopurinol one time per day and may need to increase to two times per day based on your doctor's evaluation.

It is important to know that the medication takes time to work. This means you must continue to take the medication as prescribed. Importantly, if you are taking this medication to prevent gout attacks, your symptoms of gout may increase for a short time. You may be tempted to stop taking allopurinol if this happens. Be sure to talk to your doctor if you have more gout symptoms or if you have questions about stopping the medication.

Drug forms and strengths

  • Tablet
    • 100 mg
    • 300 mg

Dosage for gout prevention

  • Initiation
  • Start with 100 mg one time per day and increase by 100 mg every week

  • Usual maintenance dose
    • 200 mg to 300 mg for mild gout
    • 400 mg to 600 mg for moderate to severe gout
    • 800 mg per day is the maximum recommended dose
    • A dose greater than 300 mg should be divided and taken two times per day

Dosage to reduce high uric acid levels caused by medications used to treat cancer

  • Usual dose
    • 600 mg to 800 mg per day along with high fluid intake for 2 to 3 days

Dosage to prevent recurrent kidney stones

  • Usual dose
    • 200 mg to 300 mg per day as a single or divided dose

If you miss a dose of allopurinol

Take a missed dose as soon as you remember. However, if it is close to the time for your next dose, skip the missed dose and take your regularly scheduled dose. Do not take a double dose to make up for a missed one.  

If you take too much allopurinol

If you take too much allopurinol, you have a higher risk of having side effects caused by this drug. If you think you have taken too much of this drug, call your doctor or local poison control center at 1-800-222-1222.

Seek emergency care (call 911) if you experience life-threatening symptoms, such as difficulty breathing; chest pain; loss of consciousness; sudden vision changes; or swelling of the face, mouth, tongue or throat.

Helpful tips when taking allopurinol

Keep these considerations in mind if your doctor prescribes allopurinol for you.

General

  • Allopurinol helps with prevention of gout attacks but does not treat the symptoms once they happen. Your doctor may give you another medicine to help reduce the symptoms of a gout attack.
  • It will take time for allopurinol to start working for you. Do not stop taking allopurinol on your own. Be sure to talk to your doctor if you have concerns about taking the medication.
  • Take allopurinol at the same time everyday so you do not miss a dose.
  • You may feel drowsy while taking allopurinol. When first starting allopurinol, be careful about driving or doing other tasks that may put you at harm if you are drowsy.

Storage

  • Keep allopurinol in its container and store at room temperature, between 68°F and 77°F (20°C to 25°C). Do not store in an area that can get hot and moist, such as the bathroom.
  • Be sure the container is closed tightly and away from the reach and sight of children.
  • This medication should not be flushed down the toilet. Talk to your pharmacist or local garbage/recycling service about how to dispose of expired or unused medication.

Alcohol

Alcohol may interfere with how well allopurinol works for you. Talk to your doctor about whether consuming alcohol is safe while taking this medication.

Effect on Weight

Loss of appetite and unexpected weight loss may occur while taking allopurinol. This is considered a serious side effect. Contact your doctor immediately if you notice these changes.

Refills

Your doctor will write the number of authorized refills on your prescription. Talk with your pharmacist if you have questions about refills.

Travel

When planning to travel, keep these tips in mind for packing your medication:

  • Bring enough medication for the entire trip based on when your next dose is due.
  • Keep your medication with you, in a purse or a carry-on bag if flying. Do not put it into a checked bag in case you are separated from your luggage.
  • Keep your medications in their original containers, if possible, to reduce delays during airport or security screening. Keep all your medications together to expedite the process.
  • Avoid leaving your medication in a parked car for extended periods to protect it from extreme temperatures (hot or cold).

Clinical Monitoring

To check that you are on the right dose of allopurinol, your doctor may do some blood tests that measure the levels of uric acid in your blood. Also, your doctor may check your liver and kidney function to make sure you are not having side effects and to make sure you are on the right amount of allopurinol.

Availability

Many pharmacies stock this drug. When filling your prescription, you can call ahead to make sure your pharmacy carries it and has it in stock.

Prior Authorization

Many insurance companies do not require a prior authorization for this drug. Health plans may prefer certain formulations over others. If a prior authorization is needed, your doctor will need to get approval from your insurance company before your insurance company will pay for your prescription.

Medications similar to allopurinol

Allopurinol belongs to a class of medications called xanthine oxidase inhibitors. Febuxostat (brand name Uloric®) is another xanthine oxidase inhibitor that is used for patients who cannot take allopurinol, do not tolerate the side effects of allopurinol, or for whom allopurinol did not work.

Discontinuing use of allopurinol

Do not stop taking this drug unless instructed by your doctor.

Healthgrades Disclaimer:

This information is for educational purposes only. It should not be interpreted as medical advice, diagnosis or treatment. Healthgrades takes every effort to ensure this information is accurate and up to date. This content is not intended to cover all possible uses, side effects, warnings, precautions, allergic reactions, or drug interactions. Do not assume that the absence of such information means the medication is safe for your personal use. Always consult your doctor, pharmacist, or healthcare professional before taking or discontinuing any medication.

Medical Reviewer: University of Illinois Chicago Drug Information Group
Last Review Date: 2021 Aug 18
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. Allopurinol. Medline Plus, National Library of Medicine, National Institutes of Health. https://medlineplus.gov/druginfo/meds/a682673.html
  2. Allopurinol Prescribing Information. Northstar Rx LLC. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=73cd79c1-6bab-4d7b-ae8b-0176efbaf5b9