Abreva
"I get cold sores about 2-3 times per year. Abreva has worked for me, but with caveats. If I can catch the sore at the very first tingle, I can limit its spread and it will heal up and go away in 3-5 days. It still looks bad for a couple of days, but at least it's not two weeks. The second to last time I used Abreva, I was traveling and couldn't get to it until about 12 hours after the first tingle. I applied Abreva, but it didn't have much effect, maybe quickening healing at best (the sore lasted seven days, untreated I'd expect a week and a half). In short, you really have to rush to apply it (and keep applying it every few hours), and it's a race against time with that first tingle, even if you aren't 100% sure it's an oncoming outbreak."