cold sores
"Cold sore sufferer since child (now 43).  Get a cold sore occasionally now (i.e. every couple of months).

PROS
If you take tablet when feel tingle/itch - have found it stopped outbreak (used twice and it did work) - at least I think it must have (can't be sure I suppose).

CONS
Don't always experience tingle/itch (i.e. asleep/sick) and cold sore breaks out - then it's too late to take (have tried twice but did not work;  in fact, I only had one cold sore on top of lip and took meds but then another broke out next day in corner of mouth).
A serious sufferer may not get required results.
Expensive (you get 3 tabs for $30 - $40 in Australia over the counter at the chemist).
You MUST have these meds on hand i.e. in bedside drawer/handbag"