A common treatment for cold sores is antiviral cream called aciclovir. A new randomised controlled trial of nearly 1,000 adults with cold sores where they either applied aciclovir cream or medical grade New Zealand manuka honey to the cold sore.
There was no significant difference in the time taken for the cold sore to heal:
8 days for aciclovir cream
9 days with New Zealand medical grade manuka honey
It should be noted that cold sores can get better within 1 to 2 weeks without treatment and the trail didn't include a no-treatment group. In addition the trail didn't show that there were any special properties of "medical grade" manuka honey as the trail didn't look at the impact of using ordinary honey.
Basically the trail results show the medical grade mauka honey worked just as well as anitvital cream.