As soon as you feel the tingle, dab about with an alco-wipe, or worst case, cotton bud dipped in metho(!) It dries it right up and the virus can't grow.
There is also a pressure point on the outer side of each big toe. You can rub it to discourage cold sores. My mum swears by tis. I think it works in reverse - whenever I wear tight shoes that rub on this spot, I seem to GET cold sores.

Anyway, back on topic - yes I have used the betadine stuff. I have tried most things for cold sores in my time. It might stop the spread, but it doesn't help the cold sore along any. Aciclovir (active ingredient) is your friend. Note to all - must not use during pregnancy as it interferes with DNA replication.

My current fave treatmentis the alcowipe at the beginning. The I move on to dabs of 50-50 bicarb-cornflour mix 5 times a day (dries it out) and then on to pawpaw ointment in the hurty stage.

But, heavens, just realised I haven't had one since June 20! That must be a record. Where IS that champagne??