I take Hall's Defense at the first sign of a cold, and it stops it in its tracks. I do believe zinc somehow shortens colds, because it as worked for me. On the other hand, I took echencia at the start of cold season, as a preventative, one year, and I came down with the worst cold of my life.  I've since read that timing is the key with echenicia, but my experience turned me off it forever. Zinc, however, I do recommend.