British scientists called for more research on Friday into the safety of painkillers after finding more evidence some may increase the risk of Heart attacks in some patients.

“We think more data and more research is needed to formally evaluate the safety of all these drugs,” Professor Julia Hippisley-Cox, of the University of Nottingham in England, said on Friday.

The findings of her study of more than 9,000 patients, which is reported in the British Medical Journal (BMJ), suggest that non-steroidal anti-inflammatory drugs, or NSAIDs, increase the danger of Heart attack.

“Our findings support existing knowledge and raise questions over additional drugs,” said Hippisley-Cox.

In April the U.S. Food and Drug Administration (FDA) recommended stronger warnings on NSAIDs, including the newer generation of anti-inflammatories - COX-2 inhibitors.

Professor Peter Weissberg of the British Heart Foundation said the link between COX-2 inhibitors and increased risk of heart attack is now well established.

“Doctors know that prescribing these drugs should be avoided in people with poor health,” he said in a statement. But he added that the question about whether regular use of other types of NSAIDs can increase the risk of heart problems has not been satisfactorily answered.

“For now, any patients who are prescribed NSAIDs should be reassured that the results indicated a very low incidence of Heart attack,” Weissberg added.

In the observational study in the BMJ the recalled drug rofecoxib (Vioxx) made by U.S. drug giant Merck and Co. Inc, diclofenac and ibuprofen were associated with a raised risk of heart attack.

Hippisley-Cox and her colleague Carol Coupland said it seems the raised health risk was not a COX-2 specific effect.

“Enough concerns may exist to warrant a reconsideration of the cardiovascular safety of all NSAIDs,” they wrote in the journal.

But the researchers added that treatment should not be changed on the basis of their study. “Further research should be done to either reassure us that these drugs are entirely safe or to find out what the risks are so that people can be properly informed,” Hippisley-Cox added.