Hey, I'm an MD at Iodine. Basically, zinc works. A Cochrane meta-analysis from 2013 showed that zinc lozenges reduce the severity and duration of common cold symptoms. It’s the closest thing we have yet to a cure for the common cold. Get the lozenges in particular (other forms don’t seem to work as well), and take ‘em on a full stomach or you can get really nauseated.
http://summaries.cochrane.org/CD001364/ARI_zinc-for-the-comm...