Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes Allopurinol. If you are concerned about side effects, discuss the risks and benefits of Allopurinol with your doctor.

The following side effects have been reported by at least 1% of people taking Allopurinol. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• Diarrhea
• dizziness
• drowsiness
• headache
• indigestion
• nausea or vomiting occurring without other side effects
• stomach pain occurring without other side effects
• hair loss

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• numbness, tingling, pain, or weakness in hands or feet
• signs of Anemia (low red blood cells; e.g., dizziness,  pale skin, unusual tiredness or weakness, shortness of breath)
• signs of clotting problems (e.g., unusual nosebleeds, bruising, blood in urine, coughing blood,  bleeding gums, cuts that don’t stop bleeding)
• signs of kidney problems (e.g., increased urination at night, decreased urine production, blood in the urine, change of urine colour, rapid weight gain)
• swelling of face, fingers, feet, or lower legs
• vision changes

Stop taking the medication and seek immediate medical attention if any of the following occur:

• chills, Fever, muscle aches or pains, nausea, or vomiting (especially if this happens with or shortly after a skin rash)
• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• signs of bleeding in the stomach (e.g., bloody, black, or tarry stools, spitting up of blood, vomiting blood or material that looks like coffee grounds)
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
• signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking Allopurinol.

100 mg
Each white-to-off-white, round, biconvex, uncoated tablet, with "AL" and "100" separated by breakline on one side and plain on the other side, contains 100 mg of allopurinol. Nonmedicinal ingredients: lactose monohydrate, cornstarch, sodium starch glycolate, povidone and stearic acid.

200 mg 
Each peach-coloured, round, biconvex, uncoated tablet, with "AL" and "200" separated by breakline on one side and plain on the other side, contains 200 mg of allopurinol. Nonmedicinal ingredients: lactose monohydrate, cornstarch, sodium starch glycolate, povidone and stearic acid, Sunset Yellow Aluminium Lake.

300 mg
Each peach-coloured, round, biconvex, uncoated tablet with "AL" and "300" separated by breakline on one side and plain on the other side, contains 300 mg of allopurinol. Nonmedicinal ingredients: lactose monohydrate, cornstarch, sodium starch glycolate, povidone and stearic acid, Sunset Yellow Aluminium Lake.

Do not take Allopurinol if you:

• are allergic to allopurinol or any ingredients of Allopurinol
• have previously developed a severe reaction to allopurinol or any ingredients of Allopurinol
• are a child (except to treat high levels of uric acid caused by cancer)
• are a nursing mother (except to treat high levels of uric acid caused by cancer)

There may be an interaction between allopurinol and any of the following:

• aluminum salts (e.g., antacids containing aluminum)
• ampicillin
• amoxicillin
• angiotensin-converting enzyme inhibitors (ACEIs; Captopril, Ramipril)
• antacids (e.g., aluminum hydroxide, calcium carbonate, magnesium hydroxide)
• Azathioprine
• Bendamustine
• Bleomycin
• Carbamazepine
• chlorpropamide
• Cyclophosphamide
• Cyclosporine
• didanosine
• diuretics (e.g., Furosemide, hydrochlorthiazide)
• Mercaptopurine
• Phenytoin
• salicylates (e.g., Asa)
• theophyllines (e.g., Aminophylline, Oxtriphylline, Theophylline)
• Warfarin

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with Allopurinol. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the Nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

Before you begin taking a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take Allopurinol.

Drowsiness/reduced alertness: Allopurinol may cause drowsiness, affecting your ability to drive or operate machinery. Avoid driving, operating machinery, or performing other potentially hazardous tasks until you have determined how you are affected by Allopurinol.

Use appropriate caution if you plan to do activities requiring alertness.

Gout: Do not start allopurinol treatment until an acute attack of gout has completely subsided, as further attacks may be caused by Allopurinol. Acute gout attacks may occur at the start of treatment with allopurinol for people who have not taken the medication before. If an acute gout attack develops after starting Allopurinol, call your doctor.

Hypersensitivity syndrome: A Anaphylaxis (severe allergic reaction) called hypersensitivity syndrome has occurred for some people with the use of allopurinol. This reaction involves a number of organs in the body and may be fatal if not treated quickly. Stop taking the medication and get immediate medical attention if you have symptoms of a severe allergic reaction, including fever, swollen glands, yellowing of the skin or eyes, or flu-like symptoms with skin rash or blistering.

Kidney function: Kidney Disease or reduced kidney function may cause Allopurinol to build up in the body, causing side effects. If you have reduced kidney function or kidney disease, discuss with your doctor how Allopurinol may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Allopurinol, and whether any special monitoring is needed.

Liver function: Allopurinol may reduce liver function and can cause liver failure. If you have liver problems, discuss with your doctor how Allopurinol may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Allopurinol, and whether any special monitoring is needed. Your doctor may want to test your liver function regularly with blood tests while you are taking Allopurinol.

If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Skin rash: If you develop a skin rash, stop taking Allopurinol and contact your doctor. The skin rash may be the first sign of a serious allergic reaction to the medication.

Pregnancy: Allopurinol is not recommended for women who are or may become pregnant unless the potential benefits outweigh the possible risks. If you are or may be pregnant, talk to your doctor about the risks and benefits of Allopurinol.

Breast-feeding: Allopurinol passes into breast milk. If you are a breast-feeding mother and are taking allopurinol, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: Children should not take allopurinol, except in cases where increased uric acid levels in the blood are associated with cancer or with Lesch-Nyhan syndrome. The safety and effectiveness of allopurinol for this age group have not been established in treatment of other conditions.

Allopurinol is an inhibitor of xanthine oxidase, a substance in the body that is responsible for the product of uric acid. It is used to prevent Gout, Kidney Stones, and kidney damage caused by uric acid. It is also used to reduce the levels of uric acid in the blood that occur because of blood disorders associated with cancer such as leukemias and lymphomas.

Allopurinol may be available under multiple brand names and/or in several different forms. Any specific brand name of Allopurinol may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of Allopurinol may not be used for all of the conditions discussed here.

Your doctor may have suggested Allopurinol for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking Allopurinol, speak to your doctor. Do not stop taking Allopurinol without consulting your doctor.

Do not give Allopurinol to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take Allopurinol if their doctor has not prescribed it.