Garlic (Allium sativum)

Administered orally and topically as a powder, oil, tablet, and raw clove. Allicin is the pharmacologically active component.

Potentially beneficial to the CV system as an antihyperlipidemic (conflicting results in recent clinical trials); also useful as an antimicrobial ( Microsporum canis , sporotrichosis, tinea pedis), antiplatelet (via increased thromboxane levels), fibrinolytic, antioxidant (increased catalase and glutathione peroxidase), antidiabetic, and vasoprotective agent (i.e., antihypertensive and protective of elastic properties of the aorta).

Note: These indications are not approved by FDA, but garlic is generally recognized as safe. Interpretation of data must take into account publication bias (preferential publication of positive findings).

Increased bleeding diathesis via inhibition of platelets mediated by COX inhibition.

Major drug interactions: Anticoagulants, antidiabetic agents, ASA, NSAIDs, plt inhibitors, herbs (danshen, dong quai, feverfew, ginger, ginkgo biloba, ginseng, horse chestnut), thrombolytic agents.

Garlic has dose-dependent side effects, including breath and body odor, possible stimulation of the uterus, GI irritation and heartburn, nausea, vomiting, diarrhea, allergic reactions, dermatitis, and other skin-related pathogenesis.

Intact cells of garlic bulbs contain alliin, an odorless, sulfur-containing amino acid. Crushed garlic causes the enzyme allinase to convert alliin to allicin—a potent antibacterial agent that is odoriferous and unstable. Ajoene, a self-condensation product of allicin, has antithrombotic activity. Fresh garlic releases allicin in the mouth during the chewing process. Dried garlic preparations lack allicin but contain alliin and allinase; they should be enteric-coated so that they will pass through the stomach into the small intestine, where alliin can be enzymatically converted to allicin. Allicin is unstable in oil. Allinase is inactivated by heat (cooking) and acid.

Potency can vary substantially among manufacturers.

Dosage: No clear consensus, but dosage varies with reason for use. Hypercholesterolemia/arteriosclerosis: German Commission E recommends 4 g/d (1.5–2 average-sized garlic cloves) of fresh garlic, or at least 5000 μg of allicin, or chewing one garlic clove daily. Extract standardized to 1.3% allicin is recommended. For Htn or antibacterial effect, 2.5 g/d or 1 clove or 300 mg of extract.

Treatment should be evaluated over a 3- to 6-mo period to determine efficacy. To treat M. canis , sporotrichosis, and tinea pedis, recommended oral dosage is 2–5 mg of allicin extract; topical treatment calls for applying sliced cloves or garlic extract (ajoene) to lesion 2–3 times daily for 1–2 wk.

Usual dosage is 300 mg of extract 2–3 times daily standardized to at least 1.3% allicin (equivalent to approx 3 g or 1 fresh clove daily).

Moderate daily consumption has no effects on normal individuals. Effects are not seen with cooked garlic.