Garlic for the common cold

Background 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 six to eight colds per year, and adults have two to four. Objectives To determine whether garlic (allium sativum) is effective for either the prevention or treatment of the common cold, when compared to placebo, no treatment or other treatments. Search strategy We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2009, issue 1), which includes the Acute Respiratory Infections Group Specialised Register; OLDMEDLINE (1950 to 1965); MEDLINE (January 1966 to March Week 3, 2009); EMBASE (1974 to March 2009); and AMED (1985 to March 2009). Selection criteria Randomised controlled trials of common cold prevention and treatment comparing garlic with placebo, no treatment or standard treatment. Data collection and analysis Two review authors independently reviewed and selected trials from searches, assessed and rated study quality, and extracted relevant data. Main results Of the five trials identified as potentially relevant from our searches, only one trial met the inclusion criteria. This trial randomly assigned 146 volunteer participants to either a garlic supplement (with 180 mg of allicin content) or a placebo (once daily) for 12 weeks. The trial reported 65 occurrences of the common cold in the placebo group compared with 24 in the garlic intervention group (P < 0.001). The number of days of illness was lower in the garlic group compared with the placebo group (111 versus 366). The number of days to recovery was similar in both groups (4.63 versus 5.63). Because only one trial met the inclusion criteria, limited conclusions can be drawn. The trial relied on self-reported episodes of the common cold, but was of reasonable quality in terms of randomisation and allocation concealment. Adverse effects included rash and odour. Authors' conclusions There is insufficient clinical trial evidence regarding the effects of garlic in preventing or treating the common cold. A single trial suggested that garlic may prevent occurrences of the common cold, but more studies are needed to validate this finding. Claims of effectiveness appear to rely largely on poor quality evidence.