Eucalyptus is a tree. The dried leaves and oil are used to make medicine. Though eucalyptus is used medicinally for many purposes, there isn’t enough scientific evidence so far to rate it as effective for any of them.Eucalyptus leaf is used for infections, fever, upset stomach, and to help loosen coughs.ucalyptus is a tree. The dried leaves and oil are used to make medicine. Though eucalyptus is used medicinally for many purposes, there isn’t enough scientific evidence so far to rate it as effective for any of them.