Researchers from the UK and Canada say Voltaren should be pulled off the market because it raises the risk of heart attack and stroke.
The painkiller diclofenac, sold as Voltaren, should be taken off the market, the research said, after finding it remains popular despite known cardiovascular risks.
But Medsafe in New Zealand said the danger had been reviewed and it was believed the benefits outweighed the risk.
In a study published this week in the journal PLOS Medicine researchers found that diclofenac, on average, was the most commonly used non-steroidal anti-inflammatory drug (NSAID) in 15 countries studied - despite being associated with more cardiovascular complications than other NSAIDs. Researchers looked at the national essential medicine lists from 100 countries, and found 74 of them listed diclofenac.
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The researchers said it was likely that diclofenac was taken by many individuals at high risk of heart attack.
"We believe there's no advantage over safer drugs, and we believe it should be withdrawn from world markets," said Dr David Henry, of the Institute for Clinical Evaluative Sciences, in Canada.
"Given the availability of safer alternatives, diclofenac should be delisted from national essential medicine lists," said study lead author Dr Patricia McGettigan, from the William Harvey Research Institute in London.
However, Medsafe said all medicines carried risks and benefits.
"In 2008 Medsafe reviewed the safety of non-selective, non-steroidal anti-inflammatory drugs (NSAIDs), such as diclofenac and concluded that the benefits of using diclofenac to treat pain and/or inflammatory conditions outweigh the potential risks for the majority of patients," said Medsafe Group manager Stewart Jessamine. He said Medsafe's advice for consumers was to use the lowest possible dose of diclofenac for the shortest time possible.
It was prescribed for 375,000 people in the year to November 2012.