In an update of a 1999 Cochrane review, the authors examined zinc's efficacy both in shortening the duration of colds and in preventing them. They considered the results of 15 randomized trials, totaling over 1300 participants.
Zinc supplements significantly reduced the severity of cold symptoms as well as the length of illness. Among people taking zinc within 24 hours of the start of symptoms, the risk for still having symptoms at the 7-day mark was about half that of those not taking zinc. In preventing colds, zinc supplements taken for at least 5 months conferred a risk for catching a cold that was only two thirds that of controls.
Zinc's side effects included a bad taste and nausea.
Cochrane Library abstract (Free abstract)
Published in Physician's First Watch February 17, 2011
اللَّهُمَّ نَجِّ الْمُسْتَضْعَفِينَ مِنَ الْمُؤْمِنِينَ اللَّهُمَّ اشْدُدْ وَطْأَتَكَ عَلَى مُضَرَ اللَّهُمَّ اجْعَلْهَا عَلَيْهِمْ سِنِينَ كَسِنِي يُوسُفَ