Proven Health Benefits of Garlic-A Review Article


Garlic, also known as Clove Garlic is part of the Lilliceae plant family. Garlic is a member of the onion family and is one of nature's most multipurpose medicinal plants. Garlic (Allium sativum), is used widely as a flavoring in cooking, but it has also been used as a medicine throughout ancient and modern account, it has been taken to prevent and treat a wide range of ailments and diseases. One of the principal active substance allicin of fresh garlic extract, which readily permeability through phospholipid membranes may contribute to its possible biological activity and containing sulfur compounds, which are believed to bring some of the health benefits. Currently, garlic is widely used for several conditions linked to the blood system and heart, including atherosclerosis (hardening of the arteries), high cholesterolheart attackcoronary heart disease, and hypertension. Garlic is also used today by some people for the prevention of lung cancerprostate cancerbreast cancerstomach cancer, rectal cancer, colon cancer, side by side it has some adverse effects.  This article reviews the importance of garlic (Allium sativum), and, their active constituents to show whether or not can be further used as potential natural sources for the development of novel drugs.

Key Words: Garlic, Allium sativum, Usage, Food. Health benefits.


Garlic is a perennial bulb, thought to be indigenous to Central Asia, Siberia and West of the Himalayas and has been grown in England from before 1540. It is now widely cultivated all over the world [1]. Garlic is a common food for flavor, spice and it is one of the herbs most commonly used in modern folkloric medicine. Garlic was an important medicine to the ancient Egyptians as listed in the medical text Codex Ebers (ca.1550 BC) especially for the working class involved in heavy labor because it was an effective remedy for many aliments such as heart problems, headache, bites, worms and tumors [2,3]. Garlic (Picture 1) is a bulbous perennial herb, closely related to the onion. It has a tall, erect flowering stem that reaches 2-3 feet in height. The plant has pink or purple flowers that bloom in mid to late summer. The part used medicinally is the bulb.  European standards specify that garlic supplements contain not less than 0.45% allicin [1].


                                           Garlic (Allium sativum)

Medicinal Species: Allium sativum

Botanical Family: Liliaceae/Alliaceae/Amaryllidaceae

Common Names (Synonyms):  Garlic  (Eng.),  lasun (Hindi), Rasonam & Lahsuna (Sanskrit), Knoblauch (Ger), Knoblauchzweibel (Ger), da suan (Chin), taisan (Jap), inniku (Jap), taesan  (Kor), tafanuwa (Hausa), ayoishi (Igbo), kitunguusumu (Swahili), ayu (Yoruba), lobha (Nepalese)[4].

Geographical Source: The geographical location for Allium sativum is relatively simple. Typically, it is grown in a temperate climate, similar to those of Central Asia. It can be found growing in the north and south hemispheres, but typically only by farmers [8].

Chemical Constituents: Alliin is odorless sulfur, containing chemical derived from the amino acid cysteine. When garlic bulbs are crushed, Alliin is converted into another compound called Allicin. Allicin is further broken down to a compound called Ajoene, which may be the substance that inhibits blockage in blood vessels from clots and atherosclerosis. The absorption and metabolism of allicin and allicin-derived compounds (Table1) are only partially understood [10]. In humans, no allicin has been detected in the serum or urine up to 24 hours after the ingestion of 25 g of raw garlic containing a significant amount of allicin [11]. Before ingestion in garlic preparations and after ingestion in the stomach, allicin likely breaks down to release a number of volatile compounds, including DAS and DADS. These organosulfur compounds are metabolized to allyl mercaptan, allyl methyl sulfide, and allyl methyl disulfide, which have been detected in human breath after garlic consumption [12-14]. Although a number of biological activities have been attributed to various allicin-derived compounds, it is not yet clear which of these compounds or metabolites actually reaches target tissues [15]. Allyl methyl sulfide but not allyl mercaptan has been detected in the urine within four hours of garlic ingestion, suggesting that this compound is absorbed into the circulation and rapidly excreted [14]. Other allicin-derived compounds, including diallyl sulfides, ajoenes, and vinyldithiins, have not been detected in human blood, urine, or stool, even after the consumption of up to 25 g of fresh garlic or 60 mg of pure allicin [15]. These findings suggest that, if they are absorbed, allicin and allicin-derived compounds are rapidly metabolized

In studies conducted in rodents, orally administrated alliin was found to be absorbed intact and to reach plasma and liver without being converted to allicin. There are no thiosulfinates (like allicin) in intact garlic cloves, and none can be generated in the stomach because alliinase would be irreversibly inhibited under acidic conditions [16].

      Allicin (released when crushed) an amino acid which gives Garlic its strong odor and is responsible for the powerful pharmacological properties of the plant germanium, Magnesium, selenium, vitamin A, vitamin C, volatile oil of which about 0.5% is composed of sulfur-containing compounds, Zinc. It also contain 65% water, 28% carbohydrate, 2.3% organosulphur compound, 2% proteins, 1.2% Free amino acid (mainly arginine), 1.5% fiber, 0.15% lipids, 0.08% phytic acid, 0.07% saponins [1, 4].

Varieties [4]:

There are two types of garlic, the hard neck and soft neck type. Genetically there are 10 major varieties or types within these two categories. Climate can have significant impact on both taste and scape production, and a variety considered a soft neck in one location may produce a flower in another. This has lead to the renaming of many strains that may instead be genetically the same plant. In Bhutan the variety Namlo Jagbvxcvey is grown, however this writer was unable to find reference to this variety in any neither of the books, nor on the internet consequently. It is possible that the aforementioned variety is an example of such a case. Due to the inability to identify the origin of this variety this writer is also unable to distinguish if this is a soft neck or hard neck variety.

  1. Hard neck varieties (Allium sativum var ophioscorodon) 

Hard neck varieties produce a flower stalk (scape), and are often termed as bolting or top setting varieties

Soft neck varieties (Allium sativum var sativum)

Soft neck varieties do not normally produce a flower stem.

      b. Pharmacological Study [4, 5]:

S-allyl cystein sulfoxide (SACS), the precursor of Allicin and garlic oil, is a sulphur containing amino acid, which is believed to account for most of its medicinal properties i.e, controlled lipid per-oxidation better than Glibenclamide and Insulin.  It also improved diabetic conditions. SACS also stimulated in vitro insulin secretion from beta cells isolated from normal rats. Anti-diabetic effects: The component Allicin increases hepatic metabolism increases the release of insulin. It exhibits Insulin sparing effect by competing with the insulin activating compound as a result more insulin becomes free to act and exert greater antidiabetic effects.

Garlic is one of the most investigated medicinal plants. During 1960 to 2007, more than three thousand research papers have been  published  on  the  chemistry  and  biological  effects  of  garlic  and garlic preparations. These studies mainly focus on the cardiovascular, anti-microbial and anti-cancer effects of garlic and, to a lesser extent, on the therapeutic indications for the treatment of hypoglycemia, heavy metal poisoning and liver dysfunction and hyperthyroidism [17] have reviewed the pharmacology and medicinal application of garlic isolated compounds for the treatment of a number of diseases (Table 1)

Table 1: Active constituent of garlic and their pharmacological actions.

Active component of















As a






































Allyl methyl








s-allyl2-pro pene

thiosul phinate














Diallyl disulfide







1,5-hexa dianyl








Methyl allyl trisulfide







2-vinyl 1,3- dithiene







3-vinyl 1,3- dithiene







S-allyl merc
















Allyl propyl disulfide







Sodium 2-propenyl








s-methyl1- cysteine









The mode of action of garlic [22]:

 Chemical analysis in the 1800s attributed garlic's activity to the sulfur containing garlic oil. In the mid-1900s an American chemist named the strong smelling liquid "allicin".The sulfur compound alliin (S-allyl-l-cysteine sulfoxide) produces allicin (diallyl thiosulfinate) via the enzyme allinase when the bulb is crushed or ground. Other sulfur compounds, peptides, steroids, terpenoids, flavonoids, and phenols have increasingly been identified as possible active ingredientsas allicin is metabolized. The exact mechanism of action underlying garlic's effects remains unknown and may vary according to the preparation and the therapeutic effect. The principal active substance of fresh garlic extract, which ready permeability through phospholipid membranes may contribute to its biological activity or allicin can penetrate very rapidly into different compartments of the cells and exert its biological effects[23].

Pharmacological Action [1]:

  1. Anti-bacterial [an  agent  that  destroys  bacteria; bactericide]
  2. Antibiotic [an agent that destroys or stops the growth of micro-organisms] (a powerful natural antibiotic which does not destroy the body's natural flora)
  3. Anthelmintic [an agent that destroys or expels intestinal worms and/or parasites; vermicide; vermifuge]
  4. Antioxidant [contributing to the oxidation  of  free radicals which are believed to contribute to premature aging and dementia] (very potent one)
  5. Antispasmodic [an agent which relieves  or  eases muscular spasms, cramps or convulsions]
  6. Blood thinner
  7. Carminative [an agent for easing griping pains, colic and expelling gas from the intestines]
  8. Anti-cancerous activities
  9. Anticoagulant [an agent that prevents the formation of clots in a liquid, as in blood]
  10. Antiseptic [an agent  for  inhibiting  the  growth  of microorganism on living tissue or destroying pathogenic or putrefactive bacteria]
  11. Anti-tumor (inhibits tumor cell formation)
  12. Anti-viral [an agent that destroys viruses]
  13. Cholagogue [an agent for increasing the flow of bile into the intestines]
  14. Diaphoretic [an agent that promotes perspiration]
  15. Digestive [aids the digestive system]
  16. Diuretic [an agent that increases the volume and flow of urine which cleanses the urinary system]
  17. Expectorant [an agent that promotes the discharge of mucous and secretions from the respiratory passages]
  18. Febrifuge [an agent that reduces or eliminates fevers]
  19. Stomachic [an agent that strengthens, stimulates or tones the stomach]
  20. Stimulant [an agent that excites or quickens the functional activity of the tissues giving more energy]

Medicinal Parts Used: Fresh bulbs, dried bulbs, and Garlic oil       

Culinary uses [1, 4, 5, 6]: It is an important spice or condiment and is chiefly used for flavorings and seasoning vegetable and meat dishes. Most often, the bulb is used eaten either raw or cooked. When cooked the whole bulb can be roasted in olive oil in an oven and eaten whole, or the cloves are used as flavorings. Garlic can also be dehydrated and preserved in oil. When home preserving in home care must be taken no get botulism, this can be avoiding by refrigerating and not keeping for more than two weeks. Garlic can also be pressed for its oil, and pickled. The garlic flower stems (scapes) are also edible and used in cooking. It is used similar to chives but has a milder taste.

Nutritional Values of Garlic [18]:

Here we list the nutritional values of garlic per 100 g (3.5 oz), percentage of RDA (Recommended Dietary Allowance) is roughly approximated using US recommendations for adults (Table 2).

                       Table 2: Nutritional Values of Garlic

Nutritional Values



623 kJ (149 kcal)


33.06 g


1 g

Dietary fiber                                           

2.1 g


0.5 g


6.36 g



(18% of RDA) 181 mg


(13% of RDA) 1.7 mg


(7% of RDA) 25 mg


(80% of RDA) 1.672 mg


(22% of RDA) 153 mg


(9% of RDA) 401 mg


(1% of RDA) 17 mg


(12% of RDA) 1.16 mg


Thiamine (B1                     

(17% of RDA) 0.2 mg

Riboflavin (B2                    

(9% of RDA) 0.11 mg

Niacin (B3)                            

(5% of RDA) 0.7 mg

Pantothenic acid (B5)          

(12% of RDA) 0.596 mg

Vitamin (B6)                            

(95% of RDA) 1.235 mg

Folate (B9)                          

(1% of RDA) 3 μg

Vitamin C                               

(38% of RDA) 31.2 mg

Other Constituents:


59 g


14.2 μg


Medicinal uses:

  1. Bacterial and Viral Conditions
  1. Fights bacteria like an antibiotic
  2. Inhibits the growth of different species of bacteria
  3. Garlic is reported to be more effective than penicillin against: The organisms responsible for cholera, dysentery and enteritis
  4. Paratyphoid disease
  5. Putrefactive intestinal bacteria
  6. Streptococcus and bacteria
  7. Typhus disease
  8. One medium clove of Garlic can equal the antibacterial action equivalent penicillin
  9. Blood Conditions
  10. Dissolves blood clots
  11. Reduces fat levels in the blood
  1. Cardiovascular Conditions
  1. Angina pectoris
  2. Arteriosclerosis
  3. Balances blood pressure
  4. Decreases triglycerides
  5. Helps maintain healthy circulation
  6. Helps prevents atherosclerosis (plaque buildup in the arteries causing blockage and possibly leading to heart attack or stroke)
  7. Improves circulation
  8. Lowers blood pressure
  9. May prevent blood clots
  10. Mild hypertension
  11. Prevents thrombosis (counteracts tendency of clot forming cells to stick together within the blood vessels)
  12. Protects against cardiovascular disease
  13. Reduces blood pressure in hypertensive conditions
  14. Thins the blood (which reduces the risk of heart attack and stroke)
  1. Ear Conditions                                                                                             
  1. Garlic oil drops can be used for
  2. Earache
  3. Ear infection are put in the ears for and
  4. Otitis media, (an ear infection) a combination herbal extract (also used as ear drops) containing
  5. Garlic
  6. Calendula,
  7. Mullein flower
  8. St. John's Wort


  1. Brain and Nervous System Conditions
  1. Epilepsy
  2. Hysteria
  1. Gastrointestinal Conditions
  1. Chronic stomach and intestinal catarrh
  2. Digestive infections
  3. Relieves belching and heaviness
  4. Relieves colic
  5. Relieves gas (flatulence)
  6. Relieves nausea
  7. Rids the body of intestinal parasites, especially pinworms
  8. Stimulates the activity of the digestive organs
  9. Ulcers
  1. Immune System Conditions
  1. Fights infection
  2. Improves resistance to infection
  3. Increases the activity of white blood cells and T-helper cells (natural killer cells), the cells that are central to the activity of the entire immune system infections of            the body
  4. Preventative measure for infectious diseases
  5. Stimulates the body’s natural defenses against foreign invaders
  6. Protects cell membranes and DNA from damage
  1. Inflammatory Conditions
  1. Arthritis
  2. Infantile catarrh
  1. Genitourinary Conditions
  1. Dropsy     
  2. Urinary infections
  3. Fluid retention
  1. Respiratory Tract Conditions
  1. Asthma
  2. Breathing difficulties
  3. Chronic bronchitis
  4. Colds (reduces symptoms faster)
  5. Coughs and hoarseness
  6. Inhibits the growth of the bacteria, Mycobacterium tuberculosis, the organism responsible for tuberculosis (high doses)
  7. Preventative measure for colds and influenza
  8. Sinusitis
  9. Upper respiratory infections (especially infections deep in the lungs and throat and in the nasal passages or sinuses)
  1. Metabolic Conditions
  1. Balances blood sugar
  2. Late-onset diabetes


  1. Liver Conditions
  1. Lowers cholesterol while increasing the level of beneficial HDL's (high-density lipoproteins) the so-called good
  2. Cholesterol
  3. May help lower homocysteine levels (similar to cholesterol which may contribute to increasing amounts of blood clots and plaque in blood vessels)
  4. Regularizes liver and gallbladder activity
  5. Stimulates the production of the liver's own detoxifying enzymes which neutralize carcinogens and other
  6. Environmental toxins
  1. Parasitic Conditions
  1. Ascaris lumbricoides (roundworm) especially fresh, raw Garlic
  1. Skin Conditions
  1. Acne
  2. Cutaneous eruptions
  3. Pimples
  1. Other Conditions
  1. Cancer (people who include more raw or cooked garlic in their diet are less likely to have certain types of cancer especially:
  2. Colon cancer
  3. Stomach cancer
  4. Skin cancer
  1. Dietary Garlic may also offer some protection against the development of:
  1. Breast cancer
  2. Laryngeal (throat) cancer
  3. Prostate cancer
  4. Stimulates cell growth and activity
  5. Tumors
  6. Wounds
  1. Externally: Garlic is used in Oil, Ointments or Poultices for:
  1. Abscesses
  2. Arthritis
  3. Dispelling hard swelling
  4. Earaches
  5. Insect bites
  6. Scrofulous sores
  7. Toothache
  8. Wounds

General doses [1]:

  1. Whole Garlic clove 2-4g/day fresh, minced garlic clove (each clove is approximately 1g)
  2. Dried 600-900mg daily
  3. Infusion: 4 grams in 150mL of water/day
  4. Fluid extract of 1:5, 4 mL/day
  5. Oil 0.03-0.12mL 3/day

The following doses have been studied in scientific research [19]:
A-By mouth

1. For hardening of the arteries: A 300 mg garlic powder tablet (Kwai, Lichtwer Pharma), taken as a single dose or three times daily for up to 4 years, has been used. Also, 150 mg of specific garlic supplement (Allicor, INAT-Farma) twice daily for 24 months has been used. Combination products containing garlic have also been used. A specific aged garlic extract supplement (Kyolic, Total Heart Health, Formula 108, Wakunga) containing 250 mg of aged garlic extract taken daily for 12 months, has been used. Also, a combination product containing 300 mg aged garlic extract, taken at a dose of four tablets daily for one year, has been used.

2. For diabetes: Garlic powder 600-1500 mg daily has been used for at least 12 weeks. A 300 mg garlic tablet (Allicor, INAT-Farma) taken two to three times daily with medications called metformin or sulfonylurea, for 4 to 24 weeks has been used.

3. For high cholesterol: A dose of 1000-7200 mg of a specific aged garlic extract (Kyolic, Wakanuga) has been used daily in divided doses for 4-6 months. A dose of 600-900 mg of a specific garlic powder tablet (Kwai, Lichtwer Pharma) has been taken daily in two or more divided doses for 6-16 weeks. Also, 300 mg of another specific garlic powder product (Garlex, Bosch Pharmaceuticals) taken twice daily for 12 weeks has been used. Also, 1,200 mg of garlic powder plus 3 grams of fish oil daily for 4 weeks, or 500 mg of garlic oil plus 600 mg of fish oil daily for 60 days, has been used.

4. For high blood pressure: 300-1500 mg of garlic tablets taken in divided doses daily for 24 weeks has been used. 2400 mg of a specific garlic powder tablet (Kwai, Lichtwer Pharma) taken as a single dose or 600 mg daily for 12 weeks has been used. Capsules containing 960-7200 mg of aged garlic extract, taken daily in up to three divided doses for up to 6 months, have been used. Specific products containing aged garlic extract include Kyolic (Garlic High Potency Everyday Formula 112, Wakunga/Wagner). 500 mg of garlic oil plus 600 mg of fish oil daily for 60 days has been used.

5. For prostate cancer: 1 mg/kg of a water-soluble garlic extract, taken daily for one month, has been used.

6. For tick bites: Capsules containing 1200 mg of garlic taken daily for 8 weeks have been used.

B-Applied to the skin

For fungal skin infections (ringworm, jock itch, athlete's foot): Garlic ingredient ajoene as a 0.4% cream, 0.6% gel, and 1% gel applied twice daily for one week has been used.

Garlic supplements/ Preparation/Dosage form [1]:

  1. Essential oil (Garlic oil)
  2. Dehydrated powder (Garlic Powder)
  3. Pills
  4. Oil macerate
  5. Extract

Drug-drug interactions [1]:

Do not use Garlic supplements without first talking to your healthcare practitioner if talking any of the medications below:

  1. Anti-platelet medications (Garlic may exaggerate the activity of medications that inhibit the action of platelets in the body) including:
  1. Aspirin
  2. Dipyidamole
  3. Indomethacin
  1. Blood-thinning medications (large quantities of garlic, either fresh or commercially prepared may increase the risk of bleeding) including:
  1. Aspirin
  2. Warfarin
  1. Sulfonylureas- A class of diabetes medications (Garlic may lower blood sugar considerably so when using garlic with these medications, blood sugar levels should be monitored must be followed closely) including:
  1. Chlorpropamide
  2. Glimepiride
  3. Glyburide
  1. Protease inhibitors- a medication used to treat people with the human immune-deficiency virus (HIV) (Garlic may reduce blood levels of protease inhibitors) including:
  1. Indinavir
  2. Ritinavir
  3. Saquinavir
  1. Statins- a class of cholesterol lowering medications (Garlic may behave similarly to Statins) including:
  1. Atorvastatin
  2. Lovastatin
  1. ACE inhibitors- a class of blood pressure lowering medications (Garlic may behave similarly to ACE inhibitors so it is recommended not to take large quantities of Garlic with any of these medications) including:
  1. Captopril
  2. Enalapril
  3. Lisinopril

Adverse effects [1, 4]:

Apart from the valuable medicinal properties, garlic may also act toxically when overdosed.

Repeated or excessive garlic ingestion produces toxic effects. The most apparent problem with using garlic in human medicine is its strong odor. A problem of clinical importance is that some people are allergic to sulfur based compounds. There were several reported allergic reactions to garlic; namely, contact dermatitis, asthma, rhinitis,

conjunctivitis, urticaria, anaphylaxis and angioedema

Adverse effects may include in both internally and externally:


  1. Upset stomach,
  2. Bloating,
  3. Bad breath,
  4. Body odor
  5. Headache
  6. Fatigue
  7. Loss of appetite
  8. Muscle aches
  9. Vertigo
  10. Allergic asthmatic reaction


A stinging sensation on the skin from handling too much fresh or dried garlic can cause blistering if applied to delicate skin handling may also cause the appearance of skin lesions contact dermatitis (skin rash). Due to Garlic's blood-thinning properties, people should not use it:

  1. With bleeding disorders such as:
  2. Hemophilia
  3. Platelet disorders

Too much Garlic can increase your risk for bleeding during or after:

  1. Delivering a baby
  2. Undergoing surgery

Caution [18]:

1. Asthma patients should not consume garlic as it may have side-effects.

2. Garlic should be avoided before surgeries or medical operations.

3. Do not consume more than 2-3 garlic cloves in a day without consulting a doctor.

Safety use [19]:

Garlic is likely safe for most people when taken by mouth appropriately. Garlic has been used safely in research for up to 7 years.

Special Precautions & Warnings [19]:

Pregnancy and breast-feeding: Garlic is likely safe to use during pregnancy when taken in the amounts normally found in food. Garlic is possibly unsafe when used in medicinal amounts during pregnancy and when breast-feeding. There is not enough reliable information about the safety of applying garlic to the skin if you are pregnant or breast-feeding. Stay on the safe side and avoid use. 
Children: Garlic is possibly safe when taken by mouth and appropriately for a short-term in children. However, garlic is possibly unsafe when taken by mouth in large doses. Some sources suggest that high doses of garlic could be dangerous or even fatal to children. The reason for this warning is not known. There is no case reports available of significant adverse events or mortality in children associated with taking garlic by mouth. When applied to the skin, garlic might cause damage to the skin that is similar to a burn.
Bleeding disorder: Garlic, especially fresh garlic, might increase the risk of bleeding. 
Diabetes: Garlic can lower blood sugar. In theory, taking garlic might make blood sugar too low in people with diabetes. 
Stomach or digestion problems: Garlic can irritate the gastrointestinal (GI) tract. Use with caution if you have stomach or digestion problems. 
Low blood pressure: Garlic can lower blood pressure. In theory, taking garlic might make blood pressure become too low in people with low blood pressure.
Surgery: Garlic might prolong bleeding and interfere with blood pressure. Garlic might also lower blood sugar levels. Stop taking garlic at least two weeks before a scheduled surgery. 

Summary [21]:

Among the uses Eleventh health benefits of garlic that are supported by human research which are widely accepted by all researchers

  1. Garlic contains compounds with potent medicinal properties
  2. Garlic is highly nutritious but has very few calories
  3. garlic can combat sickness, including the common cold
  4. the active compounds in garlic can reduce blood pressure
  5.  Garlic improves cholesterol levels, which may lower the risk of heart disease.
  6.  Garlic contains antioxidants that may help prevent alzheimer's disease and dementia.
  7. Garlic may help you live longer.
  8. Athletic performance might be improved with garlic supplements.
  9.  Eating garlic may help detoxify heavy metals in the body.
  10. Garlic may improve bone health.
  11. Garlic is easy to include in your diet and tastes absolutely delicious

Zubair Khalid Labu & Md. Mostafizur Rahaman
Department of Pharmacy
World University of Bangladesh