I used to get these things religiously. I hate them so bad it makes me want to cry. The last time I had some I was so depressed and inconsolable that my poor DH practically drove all over town talking to anyone with even half a clue to try and find something to help me.

The spoke to a pharmacists who gave him a bottle of Lysine. Told him I need to take it for the duration of this cold sore, then half a tab for two weeks after that to build up the lysine in my body. After that, take one tab whenever I am in a situation that usually leads to a cold sore (aka, split my lip on the laptop going through a closed door.. doh). This was over 12 months ago. I haven't had one since.

The websites go on about studies being inconclusive and this and that, but it has been 100% effective for me. My younger sister who gets cold sores much worse (inside the mouth and throat) started taking lysine at xmas when I got her a bottle. She too has not had a reccurance since.

ETA: The "recommended" regime is 500mg a day - but I have not needed it. 500mg a day for 2 weeks, then 1000mg when at risk.