A medicine is only made available to the public if the clinical trials have shown that the benefits of taking the medicine outweigh the risks.
Once a medicine has been licensed, information on the medicine's effects, both intended and unintended, is continuously recorded and updated.
Some side-effects may be serious while others may only be a mild inconvenience.
Everyone's reaction to a medicine is different. It is difficult to predict which side-effects you will have from taking a particular medicine, or whether you will have any side-effects at all. The important thing is to tell your prescriber or pharmacist if you are having problems with your medicine.
Common: More than 1 in 100 people who take Allopurinol
- hypersensitivity reactions including skin reactions, Stevens-Johnson syndrome or toxic epidermal necrolysis, which can be fatal. You should seek immediate medical advice if you develop a rash, fever, itching, scaly or flaking skin, unexplained or easy bruising of the skin or mucous membranes, angioedema or anaphylactic shock. Some types of skin reactions may occur with joint pains, lymphadenopathy, liver problems, kidney problems or seizures
Uncommon: More than 1 in 1000 people who take Allopurinol
Very rare: Fewer than 1 in 10,000 people who take Allopurinol
The frequency of these side-effects is unknown
If you feel unwell or if you have concerns about a side-effect, you will need to seek advice. If you feel very ill, get medical help straight away. Contact your prescriber, pharmacist, nurse or call NHS Direct on 0845 46 47.