Primary active constituents: sulfur containing amino acids, Alliin and Allicin
Allicin breaks down rapidly to other sulfur compounds.
Purported uses (dose dependent, and debatable. See EBM section):
Reduces cholesterol and triglycerides
Inhibits platelet aggregation
The antimicrobial effects of garlic are well supported. The following is an excerpt from an article in Microbes and Infection¹:
"Allicin, one of the active principles of freshly crushed garlic homogenates, has a variety of antimicrobial activities. Allicin in its pure form was found to exhibit i) antibacterial activity against a wide range of Gram-negative and Gram-positive bacteria, including multidrug-resistant enterotoxicogenic strains of Escherichia coli; ii) antifungal activity, particularly against Candida albicans; iii) antiparasitic activity, including some major human intestinal protozoan parasites such as Entamoeba histolytica and Giardia lamblia; and iv) antiviral activity. The main antimicrobial effect of allicin is due to its chemical reaction with thiol groups of various enzymes, e.g. alcohol dehydrogenase, thioredoxin reductase, and RNA polymerase, which can affect essential metabolism of cysteine proteinase activity involved in the virulence of E. histolytica."
Garlic has been shown to have anti-tumor effects in several malignancies, most notably bladder cancer. (See article below)
Safety and tolerability:
Raw garlic may cause irritation of the gastric mucosa, heartburn and flatulence. Contraindications include impending surgery due to increased risk of bleeding (with excessive, non-dietary doses).
“Consuming garlic can significantly decrease serum concentration levels (of medications). Garlic can decrease peak levels by 54% and mean trough levels by 49%. These reductions in levels can cause therapeutic failure... It is suspected that garlic induces cytochrome P450 metabolism of saquinavir. Patients taking other protease inhibitors may be affected; however, only saquinavir interaction has been reported.”²
For more possible herb-drug interactions, please reference the Sloan-Kettering herbal database.
- Ankri, Serge and Mirelman, David. Antimicrobial properties of Allicin from Garlic. Microbes and Infection, Volume 1, Issue 2, February 1999, Pages 125-129
- Piscitelli SC, et al. The effect of garlic supplements on the pharmacokinetics of saquinavir. Clin Infect.Dis. 2002;34:234-8
Garlic intake and cancer risk: an analysis using the Food and Drug Administration's evidence-based review system for the scientific evaluation of health claims. American Journal of Clinical Nutrition Vol. 89, No. 1, 257-264, January 2009
The potential application of Allium Sativum (Garlic) for the Treatment of Bladder Cancer Urologic Clinics of North America, Vol 27, Issue 1 (February 2000)
Enhanced Immunocompetence by Garglic: Role in Bladder Cancer and other Malignancies Journal of Nutrition. 2001;131:1067S-1070S
Effect of Raw Garlic vs Commercial Garlic Supplements on Plasma Lipid Concentrations in Adults with Moderate Hypercholesterolemia Archives of Int Med.,2007;167(4):346-353ol. 167 N
Garlic for Treating hypercholesterolemia. A Meta-analysis of Randomized Clinical Trials
Ann Intern Med. 2000;133:420-429.
Garlic at Dietary Doses does not Impair Platelet function Anesth Analg 2007; 105:1214-1218
Antimicrobial properties of Allicin from Garlic. Microbes and Infection. Volume 1, Issue 2, February 1999, Pages 125-129