Used to treat viral infections caused by herpes viruses, including genital herpes, cold sores, and shingles. It works by slowing the growth and spread of the virus, helping the body fight the infection. Often prescribed to reduce the frequency and severity of outbreaks when taken regularly. Also used in some cases to prevent transmission of the virus to others. Commonly taken orally in tablet form, it is converted in the body to acyclovir, the active antiviral agent.