An international team of researchers has found that Tamiflu, the popular influenza antiviral, can shorten symptoms of influenza by half a day, but does not reduce hospital admissions or complications of infection.

The study, published last week in the British Medical Journal (BMJ), shows that Tamiflu modestly reduces the time to first alleviation of symptoms, but can also cause nausea and vomiting and increases the risk of headaches and renal and psychiatric syndromes.

“The trade-off between benefits and harms should be borne in mind when making decisions to use oseltamivir for treatment, prophylaxis, or stockpiling,” concludes the study authors from The Cochrane Collaboration, an independent global healthcare research network.

The data for this most recent review came from data generated by clinical trials that have not previously been open for scrutiny by independent researchers. Efforts by the BMJ and the research team convinced drugmaker Roche, which markets Tamiflu, to release the full data, according to The Scientist.

“There is no credible way these drugs could prevent a pandemic,” Carl Heneghan, one of the lead investigators of the review and a professor at Oxford University, told reporters. “Remember, the idea of a drug is that the benefits should exceed the harms. So if you can’t find any benefits, that accentuates the harms.”

Claims about the effectiveness of such antivirals against complications are key factors in decisions made by governments around the world to stockpile these drugs for seasonal and pandemic influenza surges. The US has reportedly spent more than $1.3 billion buying a strategic reserve of antivirals, while in the UK the government has spent almost £424 million for a stockpile of about 40 million doses.

Read the study at BMJ: Oseltamivir for influenza in adults and children: systematic review of clinical study reports and summary of regulatory comments.