Allium sativum L.

Amaryllidaceae (Alliaceae)

Allii sativi bulbus

Bulb

The main constituents are the sulphur-containing amino acid alliin, which in the presence of the enzyme alliinase will be converted to allicin, ajoene, and others. Other constituents are terpenes (citral, geraniol, linalool), proteins, amino acids, minerals, vitamins, trace elements, lipids and prostaglandins (ESCOP 2003; Pharmaceutical Press Editorial Team 2013). A series of saponins, such as the sativosides and erubosides, have been isolated, and garlic also contains organo-selenium compounds (Amagase 2006).

A Cochrane review on the use of garlic as monotherapy in patients diagnosed with hypertension found insufficient evidence to support its use in lowering the risk of cardiovascular morbidity and mortality, but it may have some blood pressure lowering effect (Stabler et al. 2012). The evidence for its use for reducing some of the risk factors associated with atherosclerosis, such as peripheral arterial occlusive disease, is also not statistically significant (Jepson et al. 2013). A review of the use of garlic for the prevention of pre-eclampsia and its complications for pregnant women and their babies also did not provide sufficient evidence to recommend an increase of garlic intake (Meher and Duley 2010). A meta-analysis of the effect of garlic on hypercholesterolemia showed that prolonged use (longer than 2 months) was effective in reducing total serum cholesterol (TC) and low-density lipoprotein (LDL-c) in patients with high cholesterol, reducing the risk of coronary problems and with minor side effects. Garlic might be a safer alternative therapeutic for patients with slightly elevated cholesterol, but further studies are required (Ried et al. 2013).

Randomised controlled trials on the effectiveness of garlic either for the prevention or treatment of the common cold suggested that there is still limited clinical evidence to support this therapeutic effect. However, there is one study suggesting it may prevent occurrences of the common cold (Lissiman et al. 2012). Nevertheless, more studies are required to validate this finding. The use of garlic as an antibiotic adjuvant therapy also showed no significant evidence to support its use for lung infection (Hurley et al. 2013).