If you suspect you have the flu, the best thing to do is call your doctor or go to your local walk-in care center to be tested for flu and to seek treatment. The rapid influenza test returns results within about 15 minutes. If you test positive for flu, request a prescription for zanamivir (Relenza) or oseltamivir (Tamiflu). Each is an effective treatment for flu known to reduce the severity of symptoms and the course of the illness. The key, though, is that both medicines must be started within 24 to 48 hours of symptom onset.