“Most cold medicines only treat cold symptoms,” but Zicam Cold Remedy “shortens the duration and severity of the cold,” says the Web site for this zinc-based nasal gel. Does Zicam, which costs $11 to $12 for about a week’s supply, really work--and is it safe?

Test-tube studies have shown that high levels of zinc might curb the growth of cold viruses and boost production of infection-fighting substances. But only about half the clinical trials we looked at for nasal zinc have found that it shortens or eases a cold.

More important, studies with animals and case reports suggest that nasal zinc may cause loss of smell, possibly permanent. Last year we unearthed more than 200 complaints to the Food and Drug Administration about an impaired sense of smell, taste, or both after using zinc nasal products. And about 340 consumers have sued Matrixx Initiatives, the maker of Zicam, claiming loss of smell. Last January the company agreed to settle almost all outstanding lawsuits without admitting fault. Matrixx’s promotion of Zicam is being investigated by the Federal Trade Commission, which regulates product advertising.

Oral zinc is probably safe if you take less than 40 milligrams a day. But the evidence on its efficacy is also mixed.

CR’s take. The possible risk posed by nasal zinc outweighs any benefit. it’s not clear whether oral zinc is worth taking for colds.