Insufficient evidence for garlic in prevention or treatment of the common cold

Clinical question: 
How effective is garlic for the prevention or treatment of the common cold?
Bottom line: 
There is no conclusive evidence to recommend garlic supplements as a preventative or treatment option for the common cold. A single, small trial suggested garlic might reduce the frequency of symptoms of the common cold if taken continuously as a daily prophylactic but the results require validation. On average individuals taking garlic had colds lasting 1.52 days while those taking a placebo had colds lasting 5.01 days. There is currently no evidence to help decide whether treating common colds with garlic will reduce symptom severity or days of illness. Anecdotally, adverse events reported include odour, and minor skin or respiratory irritation. The frequency of adverse effects could not be determined from the evidence available.
Caveat: 
Only one trial that met the selection criteria was identified, limiting the conclusions that can be drawn. Inclusion and exclusion criteria were not reported, nor were differences in comorbidity or concurrent illnesses. These factors reduce the generalisability of the trial and may have introduced bias into the results. No trial was identified that looked at whether taking garlic for symptoms of the cold reduces its severity or duration. However, in the included study, the number of days to recover from a cold was similar for both groups.
Context: 
Garlic is alleged to have antimicrobial and antiviral properties that relieve the common cold, among other beneficial effects. There is widespread usage of garlic supplements. The common cold is associated with significant morbidity and economic consequences. On average, children have 6 to 8 colds per year, and adults have 2 to 4.
Review CD#: 
CD006206
PEARLS No: 
206
Date: 
October, 2009
Authored by: 
Brian R McAvoy