Aciclovir is an antiviral medicationThe tablet form of aciclovir is often taken to treat genital herpes, shingles or severe chickenpoxAciclovir is also available as a cream that can be used to treat cold sores directlySome people with weakened immune systems take aciclovir every day to prevent them from getting an infection caused by herpesIt is important to read the patient leaflet for a full list of side effects and cautions.