Alliaceae (Plant Family)
Allii sativi bulbus
Known for their pungent odor, garlic bulbs have been revered as both a food
and medicine in many cultures for millennia. Construction workers who built the
Egyptian pyramids were supposedly given huge rations of garlic to sustain their
resistance against fevers. Legend has it that gravediggers in early
eighteenth-century France drank a concoction of macerated garlic in wine to
protect themselves against a plague. And during the two world wars, military
physicians gave garlic to their patients as a preventive against gangrene.
The primary active compound in garlic is alliin, an odorless substance
derived from the sulfur-containing amino acid, cysteine. However, alliin is
found only within the intact cells of garlic. When garlic bulbs are crushed, the
cell walls are broken, and an enzyme, allinase, converts alliin into a
degradation product called allicin (diallyldisulfide-S-oxide). Allicin is an
unstable compound that gives garlic its characteristic odor. Allicin is more
active than alliin, and it readily forms other odorous sulfur-containing active
Native to central Asia, garlic now grows worldwide as a cultivated plant.
This perennial reaches a height of 25 to 70 cm (10 to 28 in.). Its stem is
either erect or crook-like, and its leaves are flat and broad. Topping the
stalks are five to seven pale flowers with reddish or greenish white petals
arranged in a loose globular cluster. The subterranean compound bulb has 4 to 20
cloves, or secondary bulbs, each one weighing about 1 g. Each clove is covered
by a silky white or green skin.
On average, 0.35% sulfur (1% of the dry weight). Alliin rapidly decomposes to
form allicin which comprises 0.25% to 1.15% of garlic cloves. Alliin content is
0.7% to 1.7% in dried bulbous garlic. Other sulfur-containing constituents
comprise about 25% to 35% of compounds in garlic after the cells have been
Commercial preparations are manufactured from whole fresh bulbous garlic,
dried bulbous garlic, or oil of garlic. The quantity of active principles in
commercial products varies depending on the method of preparation and percentage
of active compounds in fresh garlic cloves. This percentage reportedly varies by
a factor of 10. Aged garlic products (garlic fermentation products) are
odor-free. However, aged garlic products have limited therapeutic benefits
because the active principles in them are usually converted into inert
substances. Consumers should use standardized garlic products containing a
specified concentration of allicin.
Historical uses: all infections both internally and as a poultice. Used as a
warming herb and as preventive for colds and flu, menstrual pain, mouthwash, and
as a douche. Anthelmintic (expels worms).
Traditional actions: antihypertensive, anticholesterolemic, antilipidemic,
reduces platelet aggregration, vasodilator, expectorant, antihistaminic,
Clinical applications: treatment and prevention of atherosclerosis, elevated
blood lipids, and thrombosis. Also used to stabilize blood sugar level, and for
gastrointestinal infections by positively affecting intestinal flora.
Numerous in vitro and in vivo investigations show that garlic has broad
spectrum antimicrobial activity against bacteria, viruses, fungi, and intestinal
parasites (helminths). Garlic also has immune-enhancing, antioxidant, and
vasodilating activity. In both in vitro and in vivo studies, garlic produces
anti-inflammatory, blood-sugar lowering (antidiabetic), and anticancer effects.
Research on garlic shows unequivocally that it can help prevent
atherosclerosis through its effects on elevated lipids and blood pressure.
Studies on both animals and humans indicate that garlic favorably shifted the
high-density lipoprotein:low-density lipoprotein ratio toward lowered LDL and
higher HDL values. It also lowered plasma viscosity and improved both blood
fluidity and capillary blood flow. Garlic increased fibrinolytic activity,
prolonged bleeding and clotting time, and inhibited platelet aggregations.
Garlic consumption reduced blood pressure in hypertensive patients.
Double-blind clinical studies reveal that garlic lowered cholesterol and
triglyceride levels in hyperlipidemic patients, and reduced blood pressure. In a
16-week, placebo-controlled trial involving 261 patients, the treatment group
had a significant reduction in total cholesterol when compared with the placebo
group. This trend has been confirmed by two meta-analyses of investigations on
the influence of garlic on blood lipids. Garlic powder administered to patients
for a minimum of four weeks resulted in an average decline of either 9% or 12%
in total blood cholesterol. The average reduction in triglycerides was 13%.
Findings on the therapeutic effects of commercial garlic preparations were
contradictory, presumably due to variable levels of active constituents in the
commercial products used in the clinical trials. Garlic preparations can be
dried (heated or freeze-dried), distilled, extracted with garlic oils, aged, or
deodorized by unspecified processes. Allicin and ajoene (a self-condensation
product of allicin) are absent in dried garlic preparations. Furthermore,
allinase is unstable in the presence of gastric acids in the stomach. In order
to be efficacious, dried garlic products must take the form of enteric-coated
capsules or tablets.
Garlic has antioxidant properties, and antitoxic activity against carbon
tetrachloride, isoproterenol, and heavy metal poisoning. It inhibits tumor
proliferation in sarcoma, bladder tumors, isolated colon carcinoma cells, and
liver cell carcinomas. In population studies in Asia, the incidence of stomach
cancer deaths was lower in people who ate large quantities of garlic. The active
principles in garlic may exert anticancer effects by stimulating the immune
system to inhibit carcinogenesis.
Allicin probably accounts for antibiotic and antiplatelet activity. Allicin
also lowers cholesterol levels by blocking lipid synthesis and by increasing the
excretion of neutral and acidic sterols. Ajoene prevents blood clots by
inhibiting platelet aggregation in vitro and in vivo in a dose-dependent and
reversible manner. By inhibiting platelet aggregation, ajeone has a protective
effect against atherosclerosis, coronary thrombosis, and stroke.
|Dosage Ranges and Duration of
Recommended dosage (lower doses for prevention, higher doses for infection):
- 1,000 to 3,000 mg daily usually taken in encapsulated form (500 mg
- Oil: 0.03 to 0.12 ml tid
Excessive dietary intake can cause stomach upset, and topical use of garlic
can result in both burn-like skin lesions and allergic contact dermatitis.
Individuals prone to slow blood clotting should not take therapeutic doses of
garlic. Excessive intake of either dietary or nondietary sources of garlic can
increase the risk of hemorrhagic complications during surgery and postoperative
bleeding. Pregnant and lactating women should also avoid consuming garlic in
large quantities since it has abortifacient and uteroactive properties. Garlic
can alter the menstrual cycle.
Ajoene, the active antiplatelet component in garlic, potentiated the effect
of physiologically and pharmacologically active antiplatelet agents such as
dipyridamole and indomethacin in vitro (Apitz-Castro et al. 1986).
When administered to patients with myocardial infarction, the essential oil
of garlic increased fibrinolysis by 63% to 69%, thereby enhancing the activity
of warfarin (Bordia et al. 1977). Two cases of a possible interaction between
warfarin and garlic have been reported in patients stabilized on anticoagulant
therapy (Stockley 1999). In one case, the patient's INR values more than doubled
and there was an incident of hematuria eight weeks after ingestion of garlic (3
pearles/day). This situation resolved when the garlic was discontinued, but the
INR rose again when the patient started taking two garlic tablets daily. In the
other case, the patient's INR also increased more than two-fold while the
patient was taking garlic (6 tablets/day). Because of its antiplatelet and
antithrombotic activity, garlic should be used with caution in patients taking
oral anticoagulants (Rose et al. 1990).
|Regulatory and Compendial
The U.S. FDA classifies garlic as a dietary supplement. Bulbous garlic
products are sold as nonprescription drugs in France and
Apitz-Castro R, Escalante J, Vargas R, et al. Ajoene, the antiplatelet
principle of garlic, synergistically potentiates the antiaggregatory action of
prostacyclin, forskolin, indomethacin, and dipyridamole on human platelets.
Thromb Res. 1986;42(3):303-311.
Berthold HK, et al. Effect of a garlic oil preparation on serum lipoproteins
and cholesterol metabolism. JAMA. 1998;279.
Bordia AK, Joshi JK, Sanadhya YD, et al. Effect of essential oil of garlic on
serum fibrinolytic activity in patients with coronary artery disease.
Bradley PR, ed. British Herbal Compendium. Vol. 1. Dorset, England:
British Herbal Medicine Association; 1992:1:105-108.
De Smet PAGM, Keller K, Hänsel R, Chandler RF, eds. Adverse Effects of
Herbal Drugs. Berlin: Springer-Verlag; 1997:235-236.
Gruenwald J, Brendler T, Jaenicke C, et al., eds. PDR for Herbal
Medicines. Montvale, NJ: Medical Economics Co; 1998:940-941.
Kiesewetter H, Jung F, Mrowietz C, et al. Effects of garlic on blood fluidity
and fibrinolytic activity: a randomised, placebo-controlled, double-blind study.
Br J Clin Pract. 1990;44:24-29.
Mader FH. Treatment of hyperlipidaemia with garlic-powder tablets. Evidence
from the German Association of General Practitioners' multicentric
placebo-controlled double-blind study. Arzneimittelforschung. October
Murray MT. The Healing Power of Herbs: The Enlightened Person's Guide to
the Wonders of Medicinal Plants. 2nd ed. Rocklin, Calif: Prima Publishing;
Newall C, Anderson L, Phillipson J. Herbal Medicines: A Guide for
Health-care Professionals. London: Pharmaceutical Press; 1996:129-133.
Orekhov A, Tertov V, Sobenin I, Pivovorava E. Direct
antiatherosclerosis-related effects of garlic. Ann Med.
Rose KD, Croissant PD, Parliamennt CF, et al. Spontaneous spinal epidural
hematoma with associated liver dysfunction from excessive garlic ingestion: a
case report. Neurosurg. 1990;26:880-882.
Schulz V, Hänsel R, Tyler V. Rational Phytotherapy: A Physicians' Guide to
Herbal Medicine. 3rd ed. Berlin: Springer-Verlag; 1998:107-123.
Silagy C, Neil A. Garlic as a lipid lowering agent—a
meta-analysis. JR Coll Physicians Lond. 1994;28:39-45.
Steiner M, Khan AH, Holbert D, Lin RI. A double-blind crossover study in
moderately hypercholesterolemic men that compared the effect of aged garlic
extract and placebo administration on blood lipids. Am J Clin Nutr.
Stockley IH. Drug Interactions, 5th ed. London, England:
Pharmaceutical Press; 1999:240-241.
Tyler V. Herbs of Choice: The Therapeutic Use of Phytomedicinals.
Binghamton, NY: Pharmaceutical Products Press; 1994:104-115.
Tyler V. The Honest Herbal: A Sensible Guide to the Use of Herbs and
Related Remedies. 3rd ed. Binghampton, NY: Pharmaceutical Products Press;
Warshafsky S, Kramer RS, Sivak SL. Effect of garlic on total serum
cholesterol. Ann Intern Med.
Copyright © 2000 Integrative Medicine
CommunicationsThis publication contains
information relating to general principles
of medical care that should not in any event be construed as specific
instructions for individual patients. The publisher does not accept any
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The reader is advised to check product information (including package inserts)
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