If you use the Abreva right away, it shouldn't grow any bigger at all. If it's already active, there is no use in using the abreva at all.
The abreva is designed to start healing BEFORE your cold sore becomes active, that why the commercial says "use at the first tingle." If it's already a blister, then use blistex or carmex to heal it, and it usually takes about 3 to 4 days unfortunately.
I got my info from my Pharmasist at Walgreens and he was right, the next time I got one, I used the Abreva right away and it never got any bigger. Hope I helped for next time.