The three-and-a-half-year Active-A study found combining the drugs cut stroke risk by 28 per cent and MI risk by 23 per cent among AF patients.
NICE currently recommends warfarin as the most effective treatment for AF, but many patients struggle to tolerate it.
The study involved 7,554 AF patients randomly assigned to either clopidogrel 75mg daily, or placebo. All of the patients were being treated with aspirin.
Researcher Dr Salim Yusuf, of McMaster University in Ontario, said: 'Warfarin is more effective than clopidogrel plus aspirin against stroke in AF. Clopidogrel provides only about three-quarters of the benefit of warfarin over aspirin, but with only about three-quarters of the increased risk of haemorrhage.'
John Camm, professor of cardiology at St George's Hospital in London, said nearly half of patients in the UK cannot tolerate anticoagulants.
'This evidence clearly calls for a change in treating patients with AF who cannot take an oral anticoagulant, and who are also at low risk of bleeding.'
The findings were presented last week at the American College of Cardiology conference in Florida.
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