The effectiveness of H1N1 flu antiviral Tamiflu has been questioned in a new report that has stated there is no clear evidence that the drug prevents complications such as pneumonia.

Tamiflu, manufactured by Roche, has been mobilised by governments around the world to treat swine flu but research by the British Medical Journal (BMJ) has found it does not reduce influenza-related lower respiratory tract complications.

BMJ said the drug could cut flu symptoms by about a day but also induced nausea.

Roche has contested the findings.