Tamiflu is one of the antivirals in the Public Health Agency of Canada's pandemic stockpile. (Sang Tan/Associated Press)

There is no clear evidence that Tamiflu prevents certain complications of flu in otherwise healthy adults, according to a new report.

British researchers at the Cochrane Review, an international non-profit that reviews health information, looked at 20 previously published trials on the antiviral Tamiflu, or oseltamivir, for the prevention and treatment of seasonal flu.

There was insufficient data to show whether the antiviral reduces complications such as pneumonia in healthy adults, they concluded. The reviewers also confirmed that Tamiflu shortens flu symptoms by about one day.

The study appears in Tuesday's online issue of the British Medical Journal.

"Oseltamivir may reduce the risk of pneumonia in otherwise healthy people who contract flu. However, the absolute benefit is small, and side-effects and safety should also be considered," Prof. Nick Freemantle and Dr. Melanie Calvert from the University of Birmingham concluded.

The investigators left important questions about the effectiveness of Tamiflu unresolved, said the journal's editor-in-chief, Dr. Fiona Godlee.

"Governments around the world have spent billions of pounds on a drug that the scientific community now finds itself unable to judge," Godlee said in a release.

No change for WHO

The findings will not change the World Health Organization's advice, which recommends the antiviral for people at risk of complications from the H1N1 virus, such as pregnant women, the elderly, children and those with underlying medical conditions.

"This will not change our [Tamiflu] guidelines," said Charles Penn, a WHO antivirals expert.

Penn said that while past studies show Tamiflu has a modest benefit when patients with severe illness or at risk of complications are treated early, there are fewer hospital admissions and deaths.

The manufacturer of Tamiflu, Roche, said it firmly believes "in the robustness of the data."

Both the British researchers and WHO said there is little evidence to support the widespread use of Tamiflu in otherwise healthy people, a policy Britain has adopted in fighting swine flu.

Tamiflu packages warn of an increased risk of self-injury and confusion, particularly among children and teenagers, shortly after taking the drug.

With files from The Associated Press