Taking large amounts of vitamin C can cause side effects such as nausea, abdominal cramps, diarrhea and an increased risk for kidney stones. Echinacea research has suggested that it possibly works by stimulating various components of the body s immune system to fight off viral and bacterial invaders. It seems to have few side effects when used by basically healthy people on an occasional short-term basis. Sources recommend echinacea only be taken when symptoms of a cold first appear and then only for a week or two. Results are modest, with flu symptoms resolving one to four days earlier.
Zinc lozenges are another alternative to help reduce the duration and severity of cold symptoms.
A 1996 study found that adult subjects who used zinc lozenges from the onset of a cold through its completion recovered twice as fast as subjects who used a placebo. So can taking too much. The recommended daily amount is 12 milligrams for adult women and 15 milligrams for men. Most experts recommend no more than 100 milligrams of zinc per day. As therapy for colds, higher than the recommended daily amount is often recommended short term.