Acyclovir is used to treat infections caused by certain viruses, such as the herpes simplex virus that causes cold sores and genital herpes, as well as to treat chickenpox and shingles. The medicine works by reducing the reproduction of the virus inside the body, which helps reduce symptoms and speed up the healing process.
Acyclovir may also be used as a preventive measure in some cases to reduce the possibility of recurrence of the infection in people who suffer from it on an ongoing basis.