Flu antiviral drugs work only against flu viruses. They won’t help reduce symptoms from the common cold or any other flu-like illnesses caused by viruses other than flu viruses. And if you have “leftover” prescription flu medication that you’re thinking of passing along to another family member who seems to have the flu? “No, no! Please, no!” says Dr. Coffin. Only your doctor can test you to determine if you actually have the flu and then determine whether influenza medication will help you.