Garlic is popularly believed to be useful for the common cold. This belief is based on traditional use and some laboratory evidence that garlic has antibacterial and antiviral properties. We looked for studies that investigated the use of garlic for either preventing or treating the common cold. Of the five studies identified, only one fulfilled the criteria for the review. This study of 146 participants found that people who took garlic every day for three months (instead of a placebo) had fewer colds. When participants experienced a cold, the length of illness was similar in both groups (4.63 versus 5.63 days). While this one study was positive, there is a need for large, high-quality randomised controlled trials to support these findings. Possible side effects in this small trial included odour and a skin rash. More information is needed about the possible side effects of garlic.
There is no information from randomised controlled trials about whether taking garlic at the time of a cold reduces either symptom severity or the number of days of illness.