Heavy users of a group of pain medicines prescribed to nearly 400,000 New Zealanders a year have been warned about its links to an increased risk of heart attacks and strokes.
Long-term use of diclofenac at high doses is associated with a "very small increased risk" of cardiovascular events, says the Government's medicines safety authority, Medsafe.
Diclofenac is the active ingredient in Voltaren, Diclax and several other medicines in the much larger class known as non-steroidal anti-inflammatory drugs or N-SAIDs. Small-dose, short-term courses of diclofenac can be bought from a pharmacist; larger doses to treat an ongoing disorder require a doctor's prescription.
People with arthritis tend to be big users of N-SAIDs drugs to control their pain.
Fifteen per cent of adults have been diagnosed with arthritis and among those aged 65 or older the prevalence rises to around 45 per cent.
Medsafe said diclofenac was safe for most people.
"However, if you have high blood pressure, high cholesterol, diabetes, your kidneys do not work very well or you smoke, you should check with your healthcare professional that this medicine is appropriate. Use the lowest dose that works for you and stop as soon as you can.
"Patients who have had a recent [heart attack] - within the last six to 12 months - should not use diclofenac."
Arthritis NZ chief executive Sandra Kirby said, "All of these warnings we have to take very seriously. The challenge for people with arthritis is that diclofenac is one of the most commonly prescribed pain relievers.
"Our advice to people is talk to your GP because there still are non-steroidal medicines that can be prescribed that don't have the same degree of risk."
Medsafe said an expert committee's review in 2007 of heart attacks and other cardiovascular events linked to N-SAIDs found that all drugs in the class - which includes ibuprofen and Celebrex - were associated with an increased risk of serious cardiovascular events.
*Active ingredient: diclofenac
*Brands include Voltaren, Diclax, Diclofenac and Apo-Diclo.
*Warning applies to tablets, suppositories and injections, not skin gels or eyedrops.
*Last year 592,000 prescriptions for state-funded diclofenac were issued to 392,000 patients.