Article provided by Protocol for Life
The main dietary source of allicin and its precursor, alliin, is garlic (Allium sativum).1 Epidemiological studies have shown the close relation between garlic intake and overall well-being. Garlic exhibits hypolipidemic, antiplatelet, and procirculatory effects. It is thought to prevent cold symptoms through immune enhancement, and to exhibit chemopreventive action.1 Many of garlic’s effects are attributed to allicin, ajoene, and other organosulfur constituents such as S-allyl-L-cysteine. The lipid-lowering mechanism of garlic compounds is proposed to be through the inhibition of 3-hydroxy-3-methyl-Coenzyme A reductase activity in the liver.

Clinical Support for Cholesterol Reduction

In a double-blind, randomized, placebo-controlled, clinical trial with 46 mild to moderate hypercholesterolemic subjects who were not compliant with lipid-lowering therapy, supplementation with enteric-coated dehydrated garlic supplement standardized for allicin-releasing potential (9.6 mg allicin-releasing potential/day for 12 weeks) resulted in significant reduction in total cholesterol (24.2%) and LDL cholesterol (26.6%) while the placebo group showed non-significant increase in total cholesterol (2.0%) and LDL cholesterol (3.7%).3

Cautions and Interactions

Drug Interactions: Garlic can inhibit the activity of CYP2E1, which may result in the amount of circulating drugs metabolized by this enzyme, such as acetaminophen, chlorzoxazone, theophylline, some anesthetics, as well as ethanol.4 Garlic might enhance the effects of warfarin and other anticoagulant/antiplatelet drugs.5  Garlic supplementation is not recommended while taking nidrazid and anti-retroviral drugs.6,7
Food and Supplement Interactions: Concomitant use of herbs that have constituents that might affect platelet aggregation could theoretically increase the risk of bleeding in some people. These herbs include angelica, clove, danshen, ginger, ginkgo, red clover, turmeric, vitamin E, willow, and others. Concomitant use of garlic with omega-3 fatty acids can theoretically enhance antithrombotic effects.7
Interference with Lab Tests: Garlic can increase INR in patients taking warfarin.5

1. Amagase H. Clarifying the real bioactive constituents of garlic. J Nutr. Mar 2006; 136 (3 Suppl): 716S-725S.
2. Cicero AF, Ferroni A, Ertek S. Tolerability and safety of commonly used dietary supplements and nutraceuticals with lipid-lowering effects. Expert opinion on drug safety. Sep 2012; 11 (5): 753-766.
3. Kannar D, Wattanapenpaiboon N, Savige GS, Wahlqvist ML. Hypocholesterolemic effect of an enteric-coated garlic supplement. J Am Coll Nutr. Jun 2001; 20 (3): 225-231.
4. Gurley BJ, Gardner SF, Hubbard MA, et al. Cytochrome P450 phenotypic ratios for predicting herb-drug interactions in humans. Clin Pharmacol Ther. Sep 2002; 72 (3): 276-287.
5. Jiang X, Williams KM, Liauw WS, et al. Effect of ginkgo and ginger on the pharmacokinetics and pharmacodynamics of warfarin in healthy subjects. British Journal of Clinical Pharmacology. 2005; 59 (4): 425-432.
6. Dhamija P, Malhotra S, Pandhi P. Effect of oral administration of crude aqueous extract of garlic on pharmacokinetic parameters of isoniazid and rifampicin in rabbits. Pharmacology. 2006; 77 (2): 100-104.
7. Piscitelli SC, Burstein AH, Welden N, Gallicano KD, Falloon J. The effect of garlic supplements on the pharmacokinetics of saquinavir. Clin Infect Dis. Jan 15 2002; 34 (2): 234-238.

* These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.