Aciclovir (or acyclovir) is an antiviral medicine.

It treats infections caused by the herpes virus (herpes simplex), including:

* cold sores

* genital herpes

Your doctor may prescribe aciclovir to prevent you getting these infections if you have had them before or you have a weak immune system.

Acyclovir belongs to a class of drugs called antivirals. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions.

Acyclovir works by lowering the ability of the herpes virus to multiply in your body. This treats the symptoms of your infection. However, this drug doesn’t cure herpes infections. Herpes infections include cold sores, chickenpox, shingles, or genital herpes. Even with this drug, the herpes virus may still live in your body. Your symptoms may occur again later even after the symptoms of your current infection go away.