Does anti viral medication prevent you from getting herpes or does it just prevent symptom from accruing if you already have it?

Might work, but...: The 3 main antiviral drugs active against herpes (acyclocir, valacyclovir, famciclovir) can speed healing of herpes, especially the first infection and sometimes recurrent outbreaks; and reduce (but not eliminate) outbreaks and transmission to partners. They might prevent it if exposed, but only if taken before exposure; from animal studies, even an hour after exposure to the virus is too late.