Allopurinol is used to treat gout and certain types of kidney stones. It is also used to prevent increased uric acid levels in patients receiving cancer chemotherapy. These patients can have increased uric acid levels due to release of uric acid from the dying cancer cells. Allopurinol works by reducing the amount of uric acid made by the body. Increased uric acid levels can cause gout and kidney problems.

Take this medication by mouth as directed by your doctor, usually once daily. Take this medication after a meal to reduce stomach upset. If your dose is more than 300 milligrams a day, you will need to take several smaller doses during the day to get this amount (ask your doctor for directions).

It is best to drink a full glass of water with each dose and at least 8 more glasses (8 ounces each) of fluid a day. If your doctor has directed you to drink less fluid for other medical reasons, consult your doctor for further instructions. Your doctor may also instruct you on how to decrease acid in your urine (such as avoiding large amounts of ascorbic acid/vitamin C).

Dosage is based on your medical condition and response to treatment. Use this medication regularly to get the most benefit from it. To help you remember, take it at the same time(s) each day.

For the treatment of gout, it may take up to several weeks for this medicine to have an effect. You may have more gout attacks for several months after starting this medicine while the body removes extra uric acid. Allopurinol is not a pain reliever. To relieve pain from gout, continue to take your prescribed medicines for gout attacks (such as colchicine, ibuprofen, indomethacin) as directed by your doctor.

Tell your doctor if your condition lasts or gets worse.

Stomach upset, nausea, diarrhea, or drowsiness may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly.

Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor right away if you have any serious side effects, including:

• numbness/tingling of arms/legs
• easy bleeding/bruising
• unusual tiredness
• signs of kidney problems (such as change in the amount of urine, painful/bloody urination)
• signs of liver disease (such as nausea/vomiting that doesn't stop, loss of appetite, stomach/abdominal pain, yellowing eyes/skin, dark urine)
• unusual weight loss
• eye pain
• vision changes

Allopurinol may rarely cause very serious (possibly fatal) skin reactions. Some people in certain ethnic groups (such as people of African, Asian, or Native Hawaiian/Pacific Islander descent) are at greater risk. Your doctor may order a blood test to measure your risk before you start this medication. If the blood test shows you are at greater risk, your doctor should discuss the risks and benefits of allopurinol and other treatment choices with you. Get medical help right away if you develop any symptoms of a serious skin reaction, including: skin rash/blisters/peeling, itching, or swelling. Ask your doctor or pharmacist for more details.

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including:

• fever
• swollen lymph nodes
• rash
• itching/swelling (especially of the face/tongue/throat)
• severe dizziness
• trouble breathing

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Before taking allopurinol, tell your doctor or pharmacist if you are allergic to it; or if you have had a severe reaction to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of:

• liver disease
• kidney disease
• diabetes
• high blood pressure (hypertension)
• unusual diets (such as fasting)

This drug may make you drowsy. Alcohol or marijuana (cannabis) can make you more drowsy. Do not drive, use machinery, or do anything that needs alertness until you can do it safely. Alcohol may also decrease the effectiveness of this drug. Limit alcoholic beverages. Talk to your doctor if you are using marijuana (cannabis).

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.

Allopurinol passes into breast milk and may have undesirable effects on a nursing infant. Consult your doctor before breastfeeding.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (such as prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Some products that may interact with this drug are:

• "blood thinners" (such as warfarin)
• capecitabine
• didanosine
• fezolinetant

If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call 1-800-222-1222. Canada residents can call 1-844-764-7669.

Do not share this medication with others.

Lab and/or medical tests (such as uric acid blood levels, liver/kidney function, complete blood count) may be done while you are taking this medication. Keep all medical and lab appointments. Consult your doctor for more details.

If you are taking allopurinol to treat kidney stones, you may benefit from a special diet. Consult your doctor for more details.

If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.

Store at room temperature away from light and moisture. Do not store in the bathroom. Keep all medications away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company.