Valtrex (valacyclovir) is an antiviral drug. It slows the growth and spread of the herpes virus to help the body fight the infection. Valtrex is used to treat infections caused by herpes viruses, including genital herpes, cold sores, and shingles (herpes zoster) in adults. Valtrex is used to treat cold sores in children who are at least 12 years old, or chickenpox in children who are at least 2 years old. Valtrex will not cure herpes and will not prevent you from spreading the virus to other people. However, this medicine can lessen the symptoms of an infection.