Health officials have advised patients with heart problems to avoid an over-the-counter painkiller used by millions after research found it can significantly increase the risk of a heart attack or a stroke.
The Medicines and Healthcare products Regulatory Agency (MHRA) said that patients with an underlying heart condition, such as heart failure, heart disease or circulatory problems, or patients who have previously suffered heart attacks or strokes, should no longer use diclofenac.
An MHRA spokesman said the advice on the drug has been updated after a European review which found a small increased risk of heart attack and stroke.
Research published in 2011 in the journal Plos Medicine found that patients using diclofenac were found to be 40 per cent more at risk than those who were not using the drug.
In 2010 diclofenac was the most commonly prescribed non-steroidal anti-inflammatory drug (NSAID) in Britain last year, with six million prescriptions written for it. The drug is also available to buy over the counter.
During 2010, almost 17 million prescriptions were filled out for NSAIDs, which are used for pain relief and their anti-inflammatory effects in conditions including arthritis, back pain, gout, headache, and the aches and fever associated with flu.
Dr Sarah Branch, deputy director of the MHRA's Vigilance and Risk Management of Medicines Division, said: "Whilst this is a known risk and warnings have been included in patient and healthcare information for some time, this advice is now being updated.
"For many patients diclofenac will continue to provide safe and effective pain relief but it is no longer suitable for certain at-risk groups.
"Those with underlying heart conditions currently taking diclofenac should speak to their GP or pharmacist at their next routine visit to consider an alternative pain relief treatment.
"Patients with certain cardiovascular risk factors such as high blood pressure, raised cholesterol, diabetes and smoking should only use diclofenac after careful consideration with their GP or pharmacist."