The antiviral drug Tamiflu may save many lives if the world faces an influenza pandemic. But widespread use could inadvertently create new hazards, according to a new study. Significant amounts of the drug would be excreted, then flushed down toilets and end up in surface water, where it might trigger resistance in flu-infected water birds or pose unknown environmental threats. Although the researchers don't argue against the use of Tamiflu, they say the risks of its use on a large scale should be better studied.