Valacyclovir is a prodrug of acyclovir. In other words, valacyclovir is converted into acyclovir in your body. Acyclovir is the active component that fights off attacks of oral cold sores, genital herpes, and shingles in your body. Valacyclovir and acyclovir are both anti-viral medications. Valacyclovir works similarly as acyclovir and has an added advantage of a longer half-life meaning that you don’t have to take valacyclovir as frequently as acyclovir.