"Health Effects of Garlic Health Effects of Garlic ELLEN TATTELMAN, M.D., Albert Einstein College of Medicine of Yeshiva University, Bronx, New York A PDF version of this document is available. Download PDF now (4 pages /80 KB). Garlic has long been used medicinally, most recently for its cardiovascular, antineoplastic, and antimicrobial properties. Sulfur compounds, including allicin, appear to be the active components in the root bulb of the garlic plant. Studies show significant but modest lipid-lowering effects and antiplatelet activity. Significant blood pressure reduction is not consistently noted. There is some evidence for antineoplastic activity and insufficient evidence for clinical antimicrobial activity. Side effects generally are mild and uncommon. Garlic appears to have no effect on drug metabolism, but patients taking anticoagulants should be cautious. It seems prudent to stop taking high dosages of garlic seven to 10 days before surgery because garlic can prolong bleeding time. (Am Fam Physician 2005;72:103-6. Copyright© 2005 American Academy of Family Physicians.) Garlic (Allium sativum) has been used for thousands of years for medicinal purposes. Sanskrit records show its medicinal use about 5,000 years ago, and it has been used for at least 3,000 years in Chinese medicine. The Egyptians, Babylonians, Greeks, and Romans used garlic for healing purposes.1 In 1858, Pasteur noted garlic's antibacterial activity, and it was used as an antiseptic to prevent gangrene during World War I and World War II.2 Historically, garlic has been used around the world to treat many conditions, including hypertension, infections, and snakebites, and some cultures have used it to ward off evil spirits. Currently, garlic is used for reducing cholesterol levels and cardiovascular risk, as well as for its antineoplastic and antimicrobial properties.1 Pharmacology The root bulb of the garlic plant is used medicinally. It can be used fresh, dehydrated, or as a steam-distilled oil. Garlic has a high concentration of sulfur-containing compounds. The thiosulfinates, including allicin, appear to be the active substances in garlic. Allicin is formed when alliin, a sulfur-containing amino acid, comes into contact with the enzyme alliinase when raw garlic is chopped, crushed, or chewed. Dried garlic preparations containing alliin and alliinase must be enteric coated to be effective because stomach acid inhibits alliinase. Because alliinase also is deactivated by heat, cooked garlic is less powerful medicinally. The antimicrobial, hypolipidemic, antioxidant, and antithrombotic effects that have been attributed to garlic are thought to be related to allicin and other breakdown products. The antineoplastic effects may be related to the sulfur compounds or to other, unknown components.1 Uses and Efficacy Garlic has been studied extensively in vitro, in animal and human clinical trials, and in epidemiologic evaluations for its multiple medicinal properties. The quality of human trials has been variable, making comparisons among the trials difficult. Some trials are not well blinded; some are only of short duration; some have only small numbers of patients; and many are not well controlled. In addition, many different garlic preparations have been used, with unpredictable release of active ingredients. lipid-lowering effects Many randomized clinical trials have studied the effects of garlic on lipid levels. Results from two meta-analyses conducted in 19933 and 19944 of garlic's effect on total cholesterol show a significant reduction in total cholesterol levels (9 to 12 percent) compared with placebo. Since then, additional, better-designed trials have been published, with conflicting results.5-8 A meta-analysis published in 20009 that included these trials concluded that garlic is superior to placebo in reducing total cholesterol levels, but that the extent of the effect is modest (4 to 6 percent). A more recent meta-analysis10 of placebo-controlled trials using standardized dried garlic powder showed significant reductions in total cholesterol levels (19.2 mg per dL [0.50 mmol per L]), low-density lipoprotein cholesterol levels (6.7 mg per dL [0.20 mmol per L]) and triglyceride levels (21.1 mg per dL [0.24 mmol per L]) at eight to 12 weeks; these reductions were not sustained at six months of treatment. This difference in reduction may be due to differences in the studies (i.e., shorter or longer follow-up periods, fewer long-term studies, time-dependent effects of garlic,11 or nonadherence in the studies of longer duration). A European trial12 comparing garlic with a commercial lipid-lowering drug (bezafibrate, a fibric acid derivative not available in the United States) found them to be equally effective in decreasing lipids to a statistically significant extent. One trial13 of garlic extract treatment in children with hypercholesterolemia found no adverse effects, but also no significant beneficial effect on lipid levels. A trial testing garlic's effect on lipid levels, sponsored by the National Center for Complementary and Alternative Medicine, is underway.14" http://www.aafp.org/afp/20050701/103.html