TABLE 4-6 Relevant Data and Conclusions on Efficacy and Safety Reviews and Publications Identified for Garlic

Review/Clinical Trial Reference Type of Study and Sample Size Indication Control Dose Product Specification Outcomes Measured Conclusions/Results Adverse Events Profile Interactions with Pharmaceuticals, Foods or Other Dietary Supplements
Ankri and Mirelman, 1999 Review of in vitro and animal studies Antimicrobial None reported None reported Pure allicin isolated from garlic bulbs Antibacterial, antifungal, and antiparasitic activities The pure compound, allicin, inhibits the growth of a wide range of Gram-negative and Gram-positive bacteria, including multidrug-resistant enterotoxigenic strains of Escherichia coli. Allicin has shown antifungal activity against Candida albicans and antiparasitic activity against some major human intestinal protozoan parasites such as Entamoeba histolytica and Giardia lamblia. It has also has antiviral activity. None reported One study showed synergistic effects with antibiotics
Ledezma and Apitz-Castro, 2006 Review of in vitro and human studies Antifungal and anti-inflammatory Terbinafine Topical applications of ajoene for 7–15 d Pure ajoene extracted from garlic Reduction in tinea pedis infections Treatment produced a clinical cure in 79% of patients treated, with no recurrence 90 days after treatment. None reported None reported
Martin and Ernst, 2003 Review 1 trial Anti-Helicobacter pylori activity None reported Raw garlic Raw garlic cloves Reduction in Helicobacter pylori load and urease activity A study of garlic to treat Helicobacter pylori infections reported no significant effect on Helicobacter pylori load. None reported Poor methodology None reported
Rahman and Lowe, 2006 Review n=25 clinical studies Cardiovascular disease Matching placebo for some studies None reported Raw garlic, garlic powder tablets, garlic oil, aged garlic extract (20% ethanol) Reductions in serum cholesterol, platelet aggregation, blood pressure A reduction in total cholesterol was indicated in 44% of clinical trials; the most profound effect was observed in garlic’s ability to reduce platelet aggregation. Mixed results have been obtained for blood pressure and oxidative-stress reduction. None reported None reported
Ackermann et al., 2001 Review n=45 randomized trials and 73 additional studies reporting adverse events Cardiovascular disease Placebo Raw garlic, garlic powder tablets, garlic oil, aged garlic extract (20% ethanol) None reported Reductions in serum cholesterol, low-density lipoprotein (LDL), platelet aggregation, blood pressure, triglyceride levels Small reductions in the total cholesterol level at 1 mo (range of average pooled reductions,
0.03–0.45 mmol/L [1.2–17.3 mg/dL]) and at 3 mo (range of average pooled reductions
0.32–0.66 mmol/L [12.4–25.4 mg/dL]), but not at 6 mo.
Changes in LDL and triglyceride levels paralleled total cholesterol level results. No statistically significant changes in high-density lipoprotein levels.
Significant reductions in platelet aggregation and mixed effects on blood pressure outcomes.
Skin adverse effects: Dermatitis
Allergic reactions: asthma, rhinitis
Cardiovascular dysfunction: myocardial infarction
Coagulation dysfunction: bleeding, epidural hematoma, increased international normalized ratio in persons taking warfarin
Gastrointestinal tract dysfunction: small-intestine obstruction, esophageal and abdominal pain, and flatulence
None reported
Pittler and Ernst, 2007 Review of three meta-analyses of various effects in double-blind, randomized, controlled clinical trials Hypercholesterolemia Placebo None reported Garlic (unspecified) Reduction in cholesterol levels Modest reduction of 15.7 mg/dL compared to placebo over a treatment period of 8–24 wk.
In an updated meta-analysis (n=971), including 3 additional trials, the effect was diminished to 13.6 mg/dL.
In four new double-blind randomized clinical trials (n=3,670), no changes were reported in lipid levels for hypercholesterolemic patients.
None reported None reported
Sengupta et al., 2004 Review of epidemiological studies Reduced cancer risk None reported None reported None reported Cancer risk reduction Higher intake of Allium vegetables is associated with reduced risk of several types of cancers. These epidemiological findings correlate well with laboratory findings. Proposed mechanisms include inhibition of mutagenesis, modulation of enzyme activities, inhibition of DNA adduct formation, free-radical scavenging, and effects on cell proliferation and tumor growth. None reported None reported
Milner, 2006 Review Reduced cancer risk None reported Various Various Cancer risk reduction Evidence indicates the anticancer properties of fresh garlic extracts, aged garlic, garlic oil, and a number of specific organosulfur compounds generated by processing garlic. These anticarcinogenic and antitumorigenic activities arise through both dose- and temporal-related changes in a number of cellular events involved in the cancer process, including those involving drug metabolism, immune competence, cell-cycle regulation, apoptosis, and angiogenesis. The ability of garlic and related allyl sulfur compounds to block growth of tumors in the colon, lung, breast, and liver suggests general mechanisms that are not tissue specific. None reported None reported
Hu et al., 2005 Review of drug interactions Garlic extract containing 600 µg of allicin per 600 mg extract; garlic oil; aged garlic extract Activity drug interactions with garlic products Dextromethorphan and alprazolam: Administration of 1,800 mg of garlic extract twice a day (3 × 600 mg tablets) for 14 days increased the ratio of dextromethorphan to its metabolite; did not alter pharmacokinetics significantly.
Chlorzoxazone: Oral administration of garlic oil to healthy volunteers for 28 days reduced CYP2E1 activity. No alterations were observed with midazolam.
Protease inhibitors: Saquinavir—In 10 healthy volunteers, 3-wk administration of caplets containing 3.6 mg garlic powder extract twice daily decreased the plasma area under the curve by 51%, plasma concentrations by 49%, and C(max) by 54% of the protease inhibitor. These parameters did not return to baseline values after 10 d of washout. Ritonavir (400 mg single dose)—Administration of two capsules (10 mg Natural Source odorless garlic extract) for 4 days to 10 healthy volunteers did not significantly decrease the area under the curve of the protease inhibitor.
Warfarin: Two case reports suggest that the combination of warfarin and garlic products may increase clotting time and potentially cause postoperative bleeding.
Chlorpropamide: Possible interaction, causing hypoglycemia.
Acetaminophen: Administration of aged garlic extract (~6–7 cloves of garlic) for 3 mo to 16 healthy volunteers did not alter its metabolism.
Severe gastrointestinal toxicity developed in two HIV-infected patients taking garlic supplements for more than 2 wk after beginning ritonavir (400 or 600 mg twice daily) therapy. The symptoms resolved after discontinuation of therapy. The symptoms reappeared after rechallenge with garlic, even at a low ritonavir dose of 100 mg twice daily Dextromethorphan Saquinavir Warfarin Chlorpropamide

From: 4, Other Dietary Supplements for Military Personnel

Cover of Use of Dietary Supplements by Military Personnel
Use of Dietary Supplements by Military Personnel.
Institute of Medicine (US) Committee on Dietary Supplement Use by Military Personnel; Greenwood MRC, Oria M, editors.
Washington (DC): National Academies Press (US); 2008.
Copyright © 2008, National Academy of Sciences.

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