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Garlic
Garlic has many varieties, such as ramson (wild garlic, A.ursinum), garlic chives, and elephant garlic. The name Allium is derived from the Celtic word for pungent, hot, or burning; the species name, sativum, means cultivated or planted. The cloves in the garlic bulb are used medicinally and as a food component.
Uses and Benefits:
Garlic is one of the oldest herbal remedies; it was a favored food in the old Testament and has been accorded almost magical properties in various cultures. It was considered a cureall and aphrodisiac. Garlic has been employed to treat infections, wounds, respiratory conditions, diarrhea, rheumatism, heart disease, diabetes, and many other disorders. Currently, it is most often used as an antithrombotic and antioxidant herb to help prevent heart disease, atherosclerosis, and cancer. It is widely promoted to reduce abnormal cholesterol and blood pressure levels.
Pharmacology:
There is an enormous body of literature on garlic, and the following is a simplification of the controversial re­ports on its constituents and properties. Garlic contains phar­macologically active, organic sulfur compounds; the main ones are S-alkylcysteine sulfoxides and their precursors, derivatives of the amino acid cysteine such as alliin (S-allyl-L-cysteine sulfox­ide). The active constituent is thought to be allicin (diallyldisulfide­S-oxide) or a variety of allicin byproducts, which are formed only when the garlic bulb is cut, chewed, or crushed. This releases the enzyme alliinase from cells, which converts alliin into the unstable allicin. Allicin and related diallyl sulfide dimerization products pro­vide the characteristic garlic odor, and are considered to be the most important pharmacologic and medicinal compounds-many commercial products are standardized to their allicin yield.
Clinical Trials:
Numerous controlled clinical trials have been published. The most comprehensive critical evaluation of this lit­erature, commissioned by the U.S. Agency for Heathcare Re­search & Quality (AHRQ), has recently been published as a systematic review and meta-analysis. ,Many trials were found to have methodologic weaknesses, such as unclear randomiza­tion procedures, difficulty in adequately blinding for garlic's smell or odor, and lack of intention-to-treat analysis.
Anti-Cancer Effects-Over 20 case-control or cohort studies have evaluated the association of garlic with the incidence of can­cers in different cultures. In multiple studies, dietary garlic con­sumption is correlated with a decreased incidence of gastric and colorectal cancer, and limited studies have also shown promising inverse relationships with head and neck, prostate, and breast cancer. A few studies of garlic supplements, however, have failed to find a protective association with cancer incidence. An indica­tion of publication bias was found upon evaluation of all the stud­ies, and thus adequate evidence of a beneficial effect is lacking.
 
Adverse Effects:
Garlic can cause malodorous breath or body odor. Less commonly, dyspepsia, flatulence, anorexia, rhinitis, asthma, dermatitis, and other allergic reactions can also occur. Of more concern are two case reports of prolonged bleeding during surgical procedures, and one report of a spontaneous spinal epidural hematoma associated with heavy garlic use in an 87-year-old man. The cause and effect relationship between garlic and bleeding is not well established in these cases; however, since garlic may affect fibrinolysis and platelet aggregation, garlic supplementation should be considered a possible risk factor for bleeding.
Side Effects and Interactions:
In two patients taking warfarin, increased (roughly doubled) international normalized ratios (INRs) were attributed to the use of garlic products. However, these case reports lacked sufficient details to adequately assess causality.Theoretically, excessive garlic may potentiate bleeding if patients are taking anticoagulant drugs or otherwise have compromised hemostasis.
Cautions:
Sensitive patients can develop dermatitis, asthma, rhinitis, or even anaphylaxis with oral, topical, or respiratory exposure to garlic products. Such reactions are usually seen upon prolonged contact with raw garlic or after massive occupational exposure.
Preparations & Doses:
Garlic cloves can be used in several forms: whole or chopped, powdered and dried, or oil extracts. Freeze-dried garlic powder, in which alliinase is inactivated, is the prepared form that is most representative of the true composition of the fresh clove. To preserve the allicin constituents, most products are manufactured to protect alliinase from degradation by the stomach acids with a protective enteric-coating. Alternatively, oil extracts are manufactured (by maceration, steam distillation, or soaking in ethanol) that contain little allicin, but are instead composed mainly of products such as ajoene, disulfides, and SAC.
Summary Evaluation
Garlic is one of the most popular herbal medicines, and a largo variety of different types of products are available. Despite common claims and advertising, the evidence for garlic's beneficial effects on cholesterol and blood pressure is inconsistent and controversial; effects are likely to be small or clinically insignificant. Garlic supplementation appears safe for most patients who desire to use an herbal product for cardiovascular health, but the extent of any long-term beneficial effect is not well established