Swiss drugmaker Roche has vehemently rejected criticism of the effectiveness of its influenza drug Tamiflu by the Cochrane Report research network.

Speaking at the presentation of financial results for Q1 2014, CEO Severin Swan said, "Roche fundamentally disagrees with the conclusions of the report."

Swan said Tamiflu remained an important medicine against flu, but would not be drawn on whether the Cochrane Review's findings would affect the drug's sales, saying they depended on seasonal flu patterns and were very volatile.

Sales of Tamiflu rose 5% in Europe over the quarter to 344 million Swiss francs. Governments have spent billions of dollars stockpiling the drug in the wake of swine flu and avian flu epidemics.

The authors of the review said European clinical trials to which it had gained access "do not support claims that the drugs lower the risk of complications from flu, such as pneumonia, or that the benefits of the drugs outweigh their risks, which include nausea, vomiting, headaches and kidney disorders."

Cochrane pointed to a weak regulatory system in which the studies are all conducted by manufacturers, and medications are compared with a placebo rather than existing flu treatments.