Stop using this medicine and 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.
Stop using allopurinol and call your doctor at once if you have:
any skin rash, no matter how mild;
painful urination, blood in the urine;
little or no urination;
easy bruising, unusual bleeding;
numbness, tingling, burning pain;
worsening gout symptoms; 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 starting taking allopurinol oral;
rash;
drowsiness;
fever, chills;
abnormal liver function tests;
nausea, diarrhea; or
joint pain.
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.
 Allopurinol side effects (more detail)
Before taking this medicine
You should not use allopurinol if you are allergic to it.
To make sure allopurinol is safe for you, tell your doctor if you have ever had:
kidney disease;
liver disease;
diabetes;
congestive heart failure;
high blood pressure;
if you are receiving chemotherapy; or
if you have a gene variation called HLA-B*58:01 allele (your doctor will test you for this).
Tell your doctor if you are pregnant or breastfeeding.
Do not give this medicine to a child without medical advice.
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 allopurinol oral with a full glass of water. To reduce your risk of kidney stones forming, drink 8 to 10 full glasses of fluid every day, unless your doctor tells you otherwise.
If this medicine upsets your stomach, take allopurinol oral after a meal.
Allopurinol injection is given as an infusion into a vein if you are unable to take the medicine by mouth. A healthcare provider will give your first dose and may teach you how to properly use the medication by yourself.
You may need to mix the injection with a liquid (diluent) in an IV bag. When using injections by yourself, be sure you understand how to properly mix and store the medicine. Ask your doctor or pharmacist if you don't understand all instructions.
Prepare an injection only when you are ready to give it. Do not use if the medicine has changed colors or has particles in it. Call your pharmacist for new medicine.
You may need frequent medical tests. Even if you have no symptoms, tests can help your doctor determine if allopurinol is effective.
You may have gout attacks more often when you first start taking this medicine oral. Your doctor may recommend other gout medication to take with allopurinol. Keep taking the medicine as directed.
It may take 2 to 6 weeks before you have fewer gout attacks. 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 to eat or avoid.
Store at room temperature away from moisture and heat.
