Docosanol
"Every few months I get a cold sore on my bottom lip. I have naturally plump lips so you can only imagine what this looks like with a plump cold sore smack right in the middle. It makes me want to hide inside for a few days :( 

I've been prescribed Valtrex, however, I don't always have time to get a new prescription so about a month ago, I went to the pharmacy next door and bought Abreva at the first sign of my cold sore (slightly swelling blister in tact under my skin).  The first time I used it, it only decreased the speed which the cold sore formed and I was a bit disappointed. However, today, I've been applying it religiously since morning (kid you not like 3x an hour) and though it has taken nearly all day, my cold sore had reduced!!"