As a teen, why can't I take antibiotics for a viral infection?

The vast majority of viruses do run their course and exit your body via the portholes most associated with blowing, sneezing, and coughing. Most antibiotics--when taken for viral infection--can actually have a negative effect. What happens is they kill off the good, commensal bacteria that keep the bad bacteria in check, so you actually end up more vulnerable to bacterial infection in the end. While it may have some sort of placebo effect by making you feel better, it’s actually not helping you--and may even harm you, unless you get a bacterial infection on top of your viral one.