Zovirax
"If you take just one pill when you begin to feel a tingle, you won't actually get a cold sore/fever blister. It's seriously amazing! I wish I had known about this sooner. I will get a cold sore if I travel a lot or if I have any minor trauma on or around my nose/mouth. One pill when I feel it coming on stops them from forming, but you have to catch it before the blister develops. Keep taking the pill until the tingling goes away. I've never had to take more than 1 pill per occurance."