Allicin

• Cardiovascular health support
• Antimicrobial activity
• Immune system modulation
• Antioxidant protection

• Blood pressure regulation
• Cholesterol management
• Anti-inflammatory effects
• Blood glucose regulation
• Cancer prevention potential
• Detoxification support
• Gut health

Allicin (diallyl thiosulfinate) exerts its biological effects through multiple mechanisms, with its unique sulfur chemistry playing a central role. Allicin is not present in intact garlic but is formed when the garlic clove is crushed or damaged, allowing the enzyme alliinase to convert the precursor alliin to allicin. As a reactive organosulfur compound, allicin’s primary mechanism involves its thiol-disulfide exchange reactions with free thiol groups in proteins, particularly cysteine residues. This ability to modify protein thiols underlies many of allicin’s biological activities.

Allicin’s antimicrobial properties stem from its reaction with thiol-containing enzymes in microorganisms, including alcohol dehydrogenases, thioredoxin reductases, and RNA polymerases. By inhibiting these essential enzymes, allicin disrupts microbial metabolism and replication. This broad-spectrum mechanism affects bacteria (both gram-positive and gram-negative), fungi, viruses, and parasites, explaining garlic’s traditional use as a natural antimicrobial agent. In cardiovascular health, allicin inhibits the enzyme HMG-CoA reductase, which is involved in cholesterol synthesis, similar to statin medications but through a different mechanism.

It also inhibits platelet aggregation by modifying platelet surface proteins and affecting thromboxane formation, thereby reducing the risk of clot formation. Allicin modulates nitric oxide (NO) production and bioavailability, promoting vasodilation and improving blood flow. It inhibits angiotensin-converting enzyme (ACE), contributing to its blood pressure-lowering effects. As an antioxidant, allicin operates through both direct and indirect mechanisms.

It directly scavenges reactive oxygen species (ROS) and reactive nitrogen species (RNS). Indirectly, it activates nuclear factor erythroid 2-related factor 2 (Nrf2), a master regulator of cellular antioxidant responses, leading to increased expression of antioxidant enzymes like glutathione S-transferase, superoxide dismutase, and catalase. In immune function, allicin modulates the activity of immune cells, including macrophages, lymphocytes, and natural killer (NK) cells. It enhances the production of certain cytokines while suppressing others, helping to balance immune responses.

Allicin’s anti-inflammatory effects involve inhibition of nuclear factor-kappa B (NF-κB) signaling and reduction of pro-inflammatory cytokine production. It also inhibits cyclooxygenase (COX) and lipoxygenase (LOX) enzymes, reducing the production of inflammatory mediators. In glucose metabolism, allicin enhances insulin sensitivity by activating AMP-activated protein kinase (AMPK) and increasing glucose uptake in skeletal muscle and adipose tissue. It also protects pancreatic beta cells from oxidative damage.

For cancer prevention, allicin induces cell cycle arrest and apoptosis in transformed cells through multiple pathways, including activation of caspases, modulation of Bcl-2 family proteins, and disruption of mitochondrial function. It inhibits histone deacetylases (HDACs), affecting gene expression patterns related to cell proliferation and survival. Allicin also inhibits angiogenesis and metastasis by reducing vascular endothelial growth factor (VEGF) expression and matrix metalloproteinase (MMP) activity. In the digestive system, allicin modulates gut microbiota composition, potentially promoting beneficial bacteria while inhibiting pathogenic species.

It stimulates digestive enzyme secretion and bile flow, supporting overall digestive function. Importantly, allicin is highly reactive and quickly transforms into various secondary compounds in the body, including diallyl disulfide (DADS), diallyl trisulfide (DATS), and ajoene. These transformation products contribute to the overall biological effects attributed to allicin and may be responsible for some of the longer-lasting benefits of garlic consumption.

Due to allicin’s instability and variable formation in different garlic preparations, dosages are typically expressed in terms of fresh garlic equivalents or standardized allicin potential. For general health maintenance, the equivalent of 1-2 fresh garlic cloves daily (approximately 2-5 g) or supplements providing 2-5 mg of allicin potential is commonly recommended. Clinical studies have used a wide range of dosages, typically equivalent to 1-4 cloves of fresh garlic daily.

Allicin has complex bioavailability characteristics due to its high reactivity and instability. When formed (either in crushed garlic or in the intestine from alliin and alliinase), allicin has a very short half-life of less than 1 minute in blood and approximately 2-16 hours in water or oil at room temperature. Rather than being absorbed intact, allicin rapidly transforms into various secondary organosulfur compounds, including diallyl sulfide (DAS), diallyl disulfide (DADS), diallyl trisulfide (DATS), ajoene, and vinyldithiins. These transformation products, along with allicin’s direct reactions with biomolecules, are responsible for many of garlic’s biological effects.

The bioavailability of these compounds varies, with some being absorbed in the intestine and others exerting local effects in the digestive tract. Allicin’s characteristic odor can be detected on the breath and skin after consumption, indicating that some volatile metabolites are systemically distributed.

Enteric-coated formulations that protect alliinase (the enzyme that converts alliin to allicin) from stomach acid degradation, allowing allicin formation in the intestine, Consuming crushed fresh garlic after a brief rest period (10-15 minutes) to allow maximum allicin formation before ingestion, Allicin-stabilized formulations using various technologies (microencapsulation, liposomal delivery, etc.), Consuming garlic with dietary fats, which may help stabilize allicin and enhance absorption of fat-soluble transformation products, Fermented garlic preparations, which may contain more stable and bioavailable organosulfur compounds, Aged garlic extract, which contains water-soluble organosulfur compounds with better stability and bioavailability than allicin itself, Consuming garlic with vitamin C, which may help stabilize some of allicin’s transformation products, Chopping or crushing garlic and allowing it to stand before cooking to maximize allicin formation (if cooking is necessary, minimal heating is preferable)

For maximum allicin exposure, fresh crushed garlic should be consumed after allowing it to stand for 10-15 minutes (to maximize allicin formation) but before extensive transformation occurs. Garlic supplements are best taken with meals to minimize digestive discomfort and potentially enhance absorption of fat-soluble transformation products. For enteric-coated supplements designed to protect alliinase from stomach acid, taking them with food may actually be counterproductive, as the longer gastric residence time could lead to more enzyme degradation; these may be more effective when taken on an empty stomach with plenty of water. For cardiovascular benefits, consistent daily timing helps maintain steady blood levels of active metabolites.

If using multiple doses, spacing them throughout the day may provide more consistent effects. For antimicrobial benefits, more frequent administration (e.g., 2-3 times daily) may be more effective than a single larger dose. If using garlic for its potential blood pressure-lowering effects, evening administration may align with the body’s natural blood pressure regulation patterns. To minimize garlic breath, consuming garlic with milk, apples, or mint has been suggested to reduce volatile sulfur compounds, though evidence is limited.

• Breath and body odor (common, due to volatile sulfur compounds)
• Digestive discomfort (mild to moderate, 10-15% of users)
• Heartburn or gastroesophageal reflux (5-10% of users)
• Nausea (uncommon, <5% of users)
• Diarrhea (rare, particularly with high doses)
• Burning sensation in the mouth or stomach (particularly with fresh garlic)
• Allergic reactions (rare, <1% of users)
• Contact dermatitis (when applied topically)
• Increased risk of bleeding (rare, primarily with high doses)
• Hypoglycemia (rare, primarily in individuals taking blood glucose-lowering medications)

• Planned surgery (discontinue at least 7-14 days before due to potential antiplatelet effects)
• Bleeding disorders (use with caution due to antiplatelet effects)
• Gastritis, gastric ulcers, or inflammatory bowel disease (may exacerbate symptoms)
• Allergy to plants in the Allium family (garlic, onions, leeks, chives)
• Certain genetic conditions affecting red blood cells (e.g., G6PD deficiency) – high doses may trigger hemolysis

• Anticoagulant and antiplatelet medications (warfarin, aspirin, clopidogrel) – may enhance blood-thinning effects
• HIV medications (particularly non-nucleoside reverse transcriptase inhibitors and protease inhibitors) – may reduce drug levels through induction of cytochrome P450 enzymes
• Antidiabetic medications (insulin, sulfonylureas) – may enhance blood glucose-lowering effects
• Antihypertensive medications – may enhance blood pressure-lowering effects
• Isoniazid, cyclosporine, and birth control pills – potential for reduced effectiveness due to induction of metabolizing enzymes
• Thyroid medications – may interfere with thyroid function or medication absorption (theoretical concern)
• Calcium channel blockers – potential for enhanced effects (limited evidence)

No official upper limit has been established. Clinical studies have used doses equivalent to 1-4 cloves of fresh garlic (2-12 g) daily without serious adverse effects in most individuals. For allicin

specifically , daily intakes of up to 10-15 mg of allicin potential appear to be well-tolerated in healthy adults, though digestive side effects increase at higher doses. For long-term use, staying within the equivalent of 1-2 cloves of fresh garlic daily (2-5 g) or supplements providing 2-5 mg of allicin potential is generally recommended to minimize side effects

while providing potential health benefits.

Allicin and garlic supplements are regulated as dietary supplement ingredients in the United States under the Dietary Supplement Health and Education Act (DSHEA) of 1994. They have not been approved as drugs and cannot be marketed with claims to treat, cure, or prevent any disease. The FDA has not established a specific regulatory status for allicin beyond its classification as a dietary supplement ingredient. Garlic is Generally Recognized as Safe (GRAS) as a food ingredient and flavoring agent.

In 2000, the FDA allowed a qualified health claim for garlic stating that ‘consumption of garlic may reduce the risk of certain cancers,’ but this was later revoked due to insufficient scientific evidence.

Eu: In the European Union, allicin and garlic preparations are regulated as food supplements under Directive 2002/46/EC. The European Food Safety Authority (EFSA) has evaluated several health claims for garlic and allicin but has not approved any due to insufficient evidence. Garlic is approved as a traditional herbal medicinal product for the relief of cold symptoms and for the maintenance of cardiovascular health under the Traditional Herbal Medicinal Products Directive (2004/24/EC) in some EU member states.

Canada: Health Canada permits garlic and allicin as natural health product (NHP) ingredients. They are listed in the Natural Health Products Ingredients Database with approved uses for cardiovascular health, immune support, and as antimicrobials. Products containing these ingredients must have a Natural Product Number (NPN) to be legally sold in Canada. Health Canada has approved certain claims for standardized garlic extracts related to cardiovascular health.

Australia: The Therapeutic Goods Administration (TGA) classifies garlic and allicin-containing products as complementary medicines. Garlic is listed in the Australian Register of Therapeutic Goods (ARTG) with permitted indications related to cardiovascular health, immune function, and antimicrobial activity. Products must be registered or listed with the TGA before being marketed.

Japan: In Japan, garlic extracts may be classified as Foods with Function Claims (FFC) if scientific evidence supports the claimed benefits. Certain standardized garlic preparations have received approval for claims related to blood pressure and cholesterol management.

China: The China Food and Drug Administration (CFDA) recognizes garlic both as a food and as a traditional medicine in the Chinese Pharmacopoeia. Garlic and allicin preparations may be sold as health food products with specific approved health claims.

India: The Ministry of AYUSH (Ayurveda, Yoga & Naturopathy, Unani, Siddha, and Homeopathy) recognizes garlic (Lahsuna) as an important medicinal herb in the Ayurvedic Pharmacopoeia of India. The Food Safety and Standards Authority of India (FSSAI) permits garlic and its extracts in supplements and functional foods.

Low to Medium

Fresh garlic: $0.10-0.30 per day (1-2 cloves). Basic garlic powder supplements: $0.10-0.40 per day. Enteric-coated garlic supplements with standardized allicin potential: $0.30-0.80 per day. Stabilized allicin formulations: $0.50-1.20 per day. Aged garlic extract (contains minimal allicin but stable organosulfur compounds): $0.40-1.00 per day.

Allicin and garlic supplements represent one of the most cost-effective natural health products available, particularly when considering their broad spectrum of potential benefits. Fresh garlic offers the best value in terms of allicin potential per dollar, providing approximately 5-9 mg of allicin per clove at a cost of about $0.10-0.15 per clove. However, the inconvenience, odor, and variable potency of fresh garlic make supplements a practical alternative for many users. Among supplements, basic garlic powder products are the least expensive but often have poor allicin bioavailability due to alliinase inactivation by stomach acid.

Enteric-coated formulations that protect alliinase from stomach acid typically provide 3-5 times higher allicin bioavailability than non-enteric products, making them more cost-effective despite their higher price point. For cardiovascular benefits, the cost-effectiveness is high compared to pharmaceutical interventions, with garlic supplements typically costing $10-30 per month versus $50-300+ for prescription medications, though the magnitude of effect is generally more modest. For immune and antimicrobial support, stabilized allicin formulations offer the best value, though they are more expensive than basic garlic supplements. Aged garlic extract products, while containing minimal allicin, provide stable organosulfur compounds with well-documented cardiovascular benefits and excellent safety profiles, offering good value for long-term preventive use.

The market shows significant price variation for similar products, with some premium brands charging 2-3 times more than equally effective alternatives. Products that provide standardization data and have been used in clinical studies typically offer better value, even at higher price points. For maximum cost-efficiency, look for supplements that specify allicin potential or yield (ideally 4-8 mg per daily dose) and use enteric coating or other technologies to ensure allicin formation in the body. Alternatively, incorporating fresh crushed garlic into the diet (allowing it to stand for 10-15 minutes after crushing before consumption or cooking) provides the most economical source of allicin.

Allicin itself is highly unstable with a half-life of less than 1 minute in blood and approximately 2-16 hours in water or oil at room temperature. In supplement form, stabilized allicin preparations typically have a shelf life of 6-12 months

when properly stored. Supplements containing the precursors (alliin and alliinase) rather than preformed allicin are more stable, with a typical shelf life of 18-24 months. Aged garlic extract products, which contain minimal allicin but stable organosulfur compounds, may have a shelf life of 2-3 years.

Store in airtight, opaque containers away from direct light, heat, and moisture. Refrigeration (2-8°C/35-46°F) is recommended for products containing stabilized allicin to extend shelf life. For supplements containing alliin and alliinase, room temperature storage in a cool, dry place is generally acceptable, though refrigeration may extend potency. Avoid freezing unless specifically recommended by the manufacturer, as freeze-thaw cycles can affect tablet/capsule integrity and enzyme activity.

Once opened, products should ideally be used within 3-6 months for maximum potency. Blister-packed tablets or capsules maintain stability longer than bottles that are frequently opened. Keep containers tightly closed immediately after use to minimize exposure to air and moisture. For fresh garlic, store in a cool, dry, well-ventilated place (not refrigerated) to maintain allicin-forming potential.

Chopped or crushed garlic rapidly loses its allicin-forming potential and should be used immediately or within a few hours.

Heat – accelerates allicin degradation dramatically; temperatures above 40°C/104°F cause rapid breakdown, Moisture – triggers premature conversion of alliin to allicin, which then rapidly degrades, Oxygen – oxidizes allicin and its metabolites, reducing potency, Light exposure – particularly UV light can degrade allicin and its precursors, pH extremes – allicin is most stable at pH 5-6; strongly acidic or alkaline conditions accelerate degradation, Metal ions – particularly iron and copper can catalyze degradation reactions, Enzymatic degradation – various enzymes can break down allicin and its metabolites, Reaction with proteins – allicin readily reacts with protein thiols, reducing free allicin concentration, Time – even under optimal conditions, allicin gradually transforms into various secondary compounds, Cooking – temperatures above 60°C/140°F rapidly destroy alliinase activity, preventing allicin formation

Synthesis Methods

Natural Sources

Quality Considerations

Garlic (Allium sativum), the primary source of allicin, has one of the longest and most well-documented histories of medicinal use among all plants, spanning virtually every major civilization. While allicin itself was only isolated and characterized in 1944 by Chester J. Cavallito, the therapeutic properties of garlic that we now attribute to allicin have been recognized for thousands of years. Ancient Egyptian medical papyri from as early as 1550 BCE mention garlic as a remedy for a variety of ailments, including heart problems, headaches, bites, worms, and tumors.

Workers building the pyramids were given garlic to increase their strength and endurance. In ancient Greece, Hippocrates (circa 460-370 BCE), often called the father of Western medicine, prescribed garlic for a wide range of conditions, including respiratory problems, poor digestion, parasites, and fatigue. The Greek physician Dioscorides (1st century CE) documented garlic’s use as a treatment for intestinal parasites, respiratory ailments, and joint pain in his work ‘De Materia Medica.’ Ancient Roman soldiers and sailors consumed garlic to combat infections and maintain strength. Pliny the Elder (23-79 CE) listed garlic as a remedy for 61 different ailments in his ‘Natural History.’ In ancient China, garlic was used medicinally as early as 2000 BCE.

Traditional Chinese Medicine employed garlic primarily for digestive disorders and parasitic infections, as well as for its warming properties. In India’s Ayurvedic tradition, garlic (or ‘rasona,’ meaning ‘lacking one taste’) was recognized as a powerful medicine with heating, sharp, and pungent properties. It was prescribed for respiratory and digestive conditions, as well as for its rejuvenating effects. During the Middle Ages in Europe, garlic was one of the primary medicines used to combat the plague and other infectious diseases.

The 12th-century abbess and healer Hildegard of Bingen recommended garlic for parasites and food poisoning. During both World Wars, garlic was used as an antiseptic for wounds and to prevent gangrene when antibiotics were unavailable, earning it the nickname ‘Russian penicillin.’ In various Native American healing traditions, garlic and wild garlic species were used for respiratory ailments, parasites, and as general preventive medicine. Traditional use in Africa included applications for infectious diseases, hypertension, and as a protective agent against various illnesses. The scientific study of garlic’s active compounds began in the early 20th century, with significant advances in the 1940s when allicin was first isolated and identified as a key antibacterial component.

The discovery that allicin is not present in intact garlic but forms when the clove is crushed through the action of the enzyme alliinase on the precursor alliin was a crucial insight that explained why whole garlic cloves have minimal antimicrobial activity compared to crushed garlic. Since its isolation, allicin has been the subject of extensive research, confirming many of the traditional uses of garlic and revealing new potential applications in modern medicine. The historical use of garlic across diverse medical traditions and its consistent application for cardiovascular, antimicrobial, and immune-supporting purposes aligns remarkably well with modern scientific understanding of allicin’s mechanisms of action.

Ried K. Garlic lowers blood pressure in hypertensive individuals, regulates serum cholesterol, and stimulates immunity: an updated meta-analysis and review. Journal of Nutrition. 2016;146(2):389S-396S., Varshney R, Budoff MJ. Garlic and Heart Disease. Journal of Nutrition. 2016;146(2):416S-421S., Bayan L, Koulivand PH, Gorji A. Garlic: a review of potential therapeutic effects. Avicenna Journal of Phytomedicine. 2014;4(1):1-14.

Garlic Supplementation for the Prevention of Cardiovascular Events (ClinicalTrials.gov Identifier: NCT03590496), Effects of Aged Garlic Extract on Arterial Function, Inflammation, and Gut Microbiome (ClinicalTrials.gov Identifier: NCT03766100), Garlic and Vitamin D Supplementation for the Prevention of Acute Respiratory Infections (ClinicalTrials.gov Identifier: NCT03642678), Allicin-Rich Garlic Extract for the Prevention of Post-Operative Wound Infections (ClinicalTrials.gov Identifier: NCT02498145)