herpes simplex
"I have taken this medicine since it first came out.  I felt the tingle of a new sore the other day and bought a bottle of Abreva (this bottle has a pump to supply the medication which is more liquidish).  After 2 days of use I realized that no only had the Abreva NOT worked, my cold sore had spread to 3 times the original size and was still contagious (tingly and sore).  I mentioned this to my husband who said we had an older squeeze tube of Abreva (paste consistency) in his bathroom and he suggested I try that instead.  After 12 hours, 2 applications, the cold sore is already getting better.  My guess is that the makers of Abreva have watered down the active ingredient so much that it is no longer effective so they make more money."