What over the counter medication can I use for cold sore inside the mouth?

There are no over-the-counter products which have been found to shorten the length of cold sores after initial appearance. Only prescription antivirals, such as Zovirax or Valtrex along with ointments like Zovirax or Denavir have been found to effectively prevent or treat cold sores. These products will shorten their appearance from 10 days to about 5 days.