Diclofenac was recently withdrawn from being available over the counter in the United Kingdom because of concerns about serious side effects.
In January 2015 diclofenac was reclassified as prescription only.
For years, however, doctors have been anxious about diclofenac's potential heart risks.
And it can still be bought over the counter in most other countries, including the USA and parts of Europe.
It can cause heart failure and irregular heartbeats, according to the biggest study of this kind of six million people.
The report was conducted by researcher Morten Schmidt at Aarhus University Hospital in Denmark, and it concluded that patients should try out other NSAIDs before taking pills containing diclofenac as a last resort. When it is prescribed it "should be accompanied by an appropriate front package warning about its potential risks".
They found an increased rate of major adverse cardiovascular events within 30 days compared with starting other traditional NSAID or starting paracetamol. This was compared to those not taking any drug.
The researchers worked to assess the cardiac risk associated with diclofenac in individuals who weren't taking any NSAIDs, who had started taking other common NSAID pain relievers, and who were taking paracetamol (acetaminophen), commonly sold under the brand name Tylenol.
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Diclofenac is part of a class of painkillers called nonsteroidal anti-inflammatory drugs (NSAID). That is because current concerns would make them unethical.
Researchers used Danish national registry data for more than 6.3 million adults over a ten-year period to emulate clinical trial conditions to test the risk of diclofenac against other painkillers.
This was compared compared to taking paracetamol, or the NSAIDs ibuprofen or naproxen.
Shock new findings show Diclofenac - a drug used to treat back pain, headaches and arthritis - is linked to "major cardiovascular events".
"Treatment of pain and inflammation with NSAIDs may be of value to some patients to improve their quality of life despite possible side effects".
'Considering its cardiovascular and gastrointestinal risks, however, there is little justification to initiate diclofenac treatment before other traditional NSAIDs, ' they said in a statement. People who used these drugs have had on the average one attack less than with Diclofenac. The problems included cardiac arrhythmia, heart failure, ischemic stroke, stroke, premature death of cardiovascular disease and gastrointestinal haemorrhage.
Smokers and people with high blood pressure, raised cholesterol and diabetes have been advised to use the drug only after consulting their GP or pharmacist.
The researchers believe that people should finally recognize the potential health risks of the drug and reduce its usage. News is increasingly biased, corrupt, or agenda driven. Every penny we collect from donations supports vital investigative and independent journalism.