Valacyclovir is an antiviral medication primarily used to treat infections caused by certain viruses, including herpes simplex virus (which causes genital herpes and cold sores) and varicella-zoster virus (which causes shingles). It works by inhibiting viral DNA synthesis, thereby slowing the growth and spread of the virus in the body. Valacyclovir is often preferred for its convenient dosing schedule and better absorption compared to its parent compound, acyclovir. Common side effects may include headache, nausea, and abdominal pain.