How fast acyclovir works for cold sores (oral herpes) depends on how early treatment is started and the form used. When applied as a cream, it may shorten an outbreak to about 4 to 5 days in some cases. Cold sores may heal even faster when acyclovir is taken as oral tablets.
Acyclovir helps reduce how long cold sores last, but it does not eliminate the herpes virus from the body. Because of this, the virus can reactivate later and cause new outbreaks over time.
If you think you have a cold sore, see a doctor so they can confirm the diagnosis and recommend the most appropriate cold sore medicine. For people who have frequent herpes outbreaks during the year, there are specific treatment options available.