There have been a lot of studies on using zinc lozenges to reduce the length and severity of colds. Some have been positive and some have been negative. A researcher from the University of Helsinki in Finland analyzed all the studies — and found some very reassuring results for this winter's cold season.
The researcher took a look at 13 studies that matched zinc lozenges against a placebo. She found that studies using relatively small dosages of zinc showed no results. But studies using zinc acetate in larger doses showed an average 42% reduction in the duration of colds — in other words, the length of a typical cold was nearly cut in half! Studies using goodly doses of other forms of zinc shortened colds by 20%. "Benefit is observed with high doses of zinc but not with low doses," concluded the researcher, in the Open Respiratory Medicine Journal.
I recommend looking for a lozenge containing at least 20 mg of zinc (many contain only 10 mg) and take it at least 4x day during a cold. If you can't find the 20 mg variety, suck on two 10 mg lozenges. Zinc works not only by stimulating the body's immune system, but also by directly affecting the cold viruses at the back of the throat.
"Zinc lozenges may shorten the duration of colds: a systematic review." PubMed.gov. June 23, 2011.