Docosanol
"I suffer from sold sores very often (couple of times per year), and usually I treat them with Zovirax, a Aciclovir cream. Apparently in the US, you need to have a prescription for it, which I didn't have the time and money for, so I bought the next best thing the pharmacist recommended to buy off the shelf. I was very skeptical at first, but I have to say IT WORKS! After 2.5 days, my cold sore is almost gone - that's faster than how it works with the Aciclovir cream! The cold sore got smaller each time applied the cream (I applied it more than 5 times a day), and I also started to use it after the blisters had appeared already. I can definitely recommend this cream!"