Scientists were stunned to find that a drug that GlaxoSmithKline had thrown out due to bad side effects in clinical trials could help fight off two different viruses.

The drug, GSK983, was able to prevent dengue fever and Venezuelan equine encephalitus virus (VEEV), meaning it could become a vital antiviral drug, according to a Stanford University statement.

But it wasn’t all good news: the drug not only prevented infection in the cells, it also stopped them from dividing, so GSK983 might need to be paired with another drug.

During a genome-wide screen of these viruses, scientists decided to try GSK983 to see if it could stop RNA-based viruses from replicating within a cell. The key to stopping RNA is to block a protein key to creating it. However, GSK983 appears to also prevent the cells from copying as well, and cells need to copy in order to not die.

So scientists were able to introduce a different building block that could only be used for DNA in the cells, allows the cells to continue dividing normally even after defeating the viruses.