Abreva works to for cold sores caused by the HSV virus around the mouth only (do not use this on your genitals ahem). It's active ingredient is docosanol, an anti viral agent that prevents the virus from spreading to the surrounding cells that have been treated with the cream.
Many people say it works, and the tricky part with medicine is that you never know how you might respond. In my experience, if you're someone who has had cold sores for years and multiple breakouts, there is very limited efficiency in seeing any effect at all. Again, that is my experience as someone who gets sick a lot (and hence a lot of breakouts) where my standard break out lasts around 2-3days before healing, with minor discomfort.
Moral of the story: don't knock it till you try it, but I tried it and it's getting knocked.

I am very disappointed in this product. I get many cold soars, almost one every month and I usually just let them run their corse and wait until it heals on it's own. However, I wasn't feeling too well and already looked awful and did not want a cold soar on my face. I purchased Abreva a very small tube for a very hefty price.

It did nothing for me. I was shocked as I had used cold soar creams as a child and prescribed creams always seemed to work on me, this just did nothing. I will probably pay a visit to my doctor the next cold soar I get to receive a stronger or a better product for myself.

One of the better cold sore creams out there