Aciclovir 800 mg is an antiviral medicine used to treat infections caused by herpes viruses.

It works by slowing the growth and spread of the virus in the body. It is commonly used to treat conditions such as herpes simplex infections (cold sores, genital herpes), shingles (herpes zoster), and chickenpox.

This medication is most effective when started as soon as possible after the first signs or symptoms appear.