Garlic

Introduction Overview

Generic Name

garlic

Brand Name

Garlic Oil, Garlix, Garlicin Cardio, Garlinase 5000

Dosage Form

oral capsule, oral tablet

Drug Class

Herbal products

Pharmacokinetics

Absorption:
Garlic taken orally undergoes absorption primarily in the gastrointestinal tract, with bioavailability influenced by the form of garlic consumed. Raw garlic contains allicin, the unstable active compound, which is rapidly converted into various sulfur-containing metabolites after ingestion. These metabolites, including ajoene, diallyl sulfides, and vinyldithiins, are absorbed through the intestinal mucosa. The instability of allicin means its concentration can vary considerably, especially in aged or deodorized garlic products where allicin content is significantly reduced, impacting systemic availability. Absorption rates can be affected by food presence, with fat-containing meals potentially enhancing bioavailability of lipophilic garlic components.

Distribution:
Following absorption, garlic’s bioactive sulfur compounds distribute systemically, associating with plasma proteins and cellular membranes. Studies indicate garlic metabolites are widely distributed, including to cardiovascular tissues, which may underlie its reported cardioprotective effects. Certain compounds such as ajoene irreversibly bind to erythrocytes, which may prolong their biological effect. The extent of distribution can vary based on the specific garlic preparation, dosage, and individual metabolic differences. Because garlic compounds are lipophilic, they readily cross lipid membranes; however, detailed pharmacokinetic distribution studies in humans are limited and largely extrapolated from animal models.

Metabolism:
Garlic constituents undergo extensive hepatic metabolism. Allicin and other thiosulfinates are rapidly metabolized into a range of organosulfur compounds, including allyl methyl sulfide, diallyl disulfide, and allyl mercaptan. Phase I enzymatic processes, primarily involving cytochrome P450 enzymes, and Phase II conjugation pathways modify these metabolites to facilitate elimination. Garlic’s metabolic interactions with drug-metabolizing enzymes have been noted, including induction or inhibition of CYP isoforms (e.g., CYP3A4), which can alter the metabolism of concomitant medications. The metabolic pathways are complex and depend on the garlic form ingested.

Elimination:
Excretion of garlic metabolites occurs primarily via renal and pulmonary routes. Volatile sulfur-containing metabolites are exhaled through the lungs, contributing to characteristic garlic breath. Renal elimination occurs through excretion of water-soluble metabolites conjugated in the liver. The half-life of active metabolites varies; some sulfur compounds have prolonged biological activity despite rapid elimination due to protein binding or cellular uptake. The elimination profile suggests that dosing frequency should consider metabolite persistence and potential cumulative effects.

Dosage Forms

Available Dosage Forms:
Garlic is available predominantly in oral formulations including capsules and tablets. Commercial products vary widely, with some containing garlic powder, garlic oil, or deodorized garlic extracts. The commonly marketed dosage forms include:
- Oral capsules containing garlic oil or powder (dosage strengths vary by manufacturer; typical doses range from 300 mg to 1200 mg garlic equivalent per day).
- Oral tablets formulated with garlic powder or standardized extracts often designed for controlled or delayed release.
- Some products include aged garlic extracts (AGE) intended to reduce odor and stabilize bioactive components.
Dosages for Adults and Adolescents:
Standardized garlic formulations are typically dosed at 600–1200 mg daily, often divided into two to three doses. For cardiovascular indications such as hypertension or hyperlipidemia, clinical trials have employed doses within this range, with duration of therapy extending from several weeks to months. Capsules delivering approximately 1.3% standardized allicin content per dose are often referenced in clinical research. There is no established pediatric dosing due to limited safety data; caution is advised.
Specific Patient Populations:
Garlic use in pregnancy is generally considered safe when used as a food flavoring; however, medicinal dosages should be avoided or used with medical supervision. Breastfeeding safety data is limited. Patients with bleeding disorders or those on anticoagulant therapy require careful consideration due to garlic’s antiplatelet effects. Use in children is not recommended without consultation due to potential toxicity at high doses. Adjustments in dosing or discontinuation may be required prior to surgical procedures to minimize bleeding risk.

Mechanism Of Action

Garlic exerts its therapeutic effects primarily through its sulfur-containing compounds, particularly allicin and its derivatives. Upon crushing or chopping fresh garlic, the enzyme alliinase converts alliin to allicin, the principal bioactive molecule responsible for garlic's potent biological activity. Allicin interacts with thiol groups in various enzymes and proteins, thereby modifying their function and initiating downstream biochemical effects.

At the cellular level, allicin and other organosulfur compounds inhibit the activity of cyclooxygenase and lipoxygenase pathways, reducing the synthesis of pro-inflammatory prostaglandins and leukotrienes. This modulation contributes to garlic's anti-inflammatory and antiplatelet effects. Garlic’s compounds also induce nitric oxide synthase, enhancing nitric oxide production, which promotes vasodilation and improved endothelial function, underlying its potentially beneficial effects in hypertension and coronary artery disease.

Further, garlic exhibits antioxidant properties by scavenging reactive oxygen species and increasing glutathione levels, protecting cells from oxidative stress-induced damage. Its antimicrobial action is mediated through the disruption of microbial membrane integrity and inhibition of key microbial enzymes, which provides efficacy against bacteria, fungi, and viruses.

Comparatively, garlic’s mechanism differs from conventional pharmaceuticals in its multi-targeted approach and use of reactive sulfur species. Clinical studies have demonstrated garlic’s ability to reduce low-density lipoprotein (LDL) cholesterol and platelet aggregation, although potency and consistency may vary due to preparation differences. Ongoing research explores its synergistic effects with cardiovascular drugs and its role in modulating immune function.

Pharmacological Actions

Antimicrobial activity against bacteria, fungi, and viruses through disruption of microbial membranes.
Antioxidant effects via reactive oxygen species scavenging and enhancement of intracellular glutathione.
Modulation of lipid metabolism leading to reduced serum total cholesterol and LDL cholesterol.
Antiplatelet and anticoagulant effects by inhibition of platelet aggregation and thromboxane synthesis.
Vasodilatory action mediated by increased nitric oxide production improving endothelial function.
Anti-inflammatory effects through inhibition of cyclooxygenase and lipoxygenase pathways.
Immunomodulatory properties enhancing macrophage and natural killer cell activity.
Antihypertensive effects attributed to vasodilation and reduced peripheral vascular resistance.
Potential anticancer activity via induction of apoptosis and inhibition of tumor cell proliferation.
Enhancement of detoxification enzymes contributing to chemopreventive properties.
Reduction of Helicobacter pylori colonization in gastrointestinal mucosa.
Possible improvement of insulin sensitivity and glycemic control in metabolic disorders.
Inhibition of platelet aggregation leading to prolonged bleeding time and anticoagulant action.
Modulation of cytochrome P450 enzyme activity impacting drug metabolism.
Anti-parasitic effects demonstrated in certain protozoal and helminth infections.

Therapeutic Or Clinical Uses

Adjunctive therapy for mild to moderate hypertension to lower blood pressure.
Management of hyperlipidemia by reducing total and LDL cholesterol levels.
Potential adjunct in coronary artery disease to improve vascular function and reduce atherosclerosis.
Topical use for fungal skin infections such as athlete's foot, ringworm, and jock itch.
Prevention of tick bites through topical application in endemic areas.
Supportive treatment to reduce Helicobacter pylori infection in gastric ulcers.
Alternative or complementary use in certain cancers including stomach, colon, and rectal cancers.
Use as a dietary supplement to boost immune function and general health.
Traditional use to alleviate symptoms of digestive disorders and stimulate appetite.
Investigational use for prevention of common cold, though clinical evidence remains insufficient.
Circulatory enhancement in peripheral arterial diseases and intermittent claudication.
Adjunctive use to improve glycemic control in type 2 diabetes mellitus.
Reduction of platelet aggregation in patients at risk for thrombotic events.
Use in alternative medicine for respiratory infections and inflammatory conditions.
Topical application in wound healing and treatment of skin infections.

Side Or Adverse Effects

Unpleasant garlic breath and body odor, especially with raw garlic ingestion.
Gastrointestinal discomfort including heartburn, nausea, vomiting, gas, and diarrhea.
Allergic reactions such as rash, itching, or swelling particularly with topical use.
Easy bruising or prolonged bleeding due to antiplatelet and anticoagulant effects.
Potential for skin redness, swelling, or blistering upon topical application.
Rare cases of anaphylaxis or severe hypersensitivity reactions.
Interaction-related side effects including increased bleeding risk when combined with anticoagulants or NSAIDs.
Possible exacerbation of stomach ulcers or gastrointestinal irritation in sensitive individuals.
Headache or dizziness reported sporadically during high-dose supplementation.
Potential interference with thyroid function in susceptible patients, though evidence is limited.
Mild hemolysis reported rarely in patients with glucose-6-phosphate dehydrogenase deficiency.
Contact dermatitis from topical exposure to garlic preparations.
Transient alterations in taste perception or oral mucosa irritation.
Photosensitivity reactions with topical garlic compounds have been occasionally reported.
Possible lowering of blood pressure beyond desired levels causing hypotension.

Precautions

Use cautiously in patients with bleeding disorders or those taking anticoagulant or antiplatelet medications.
Advise discontinuation at least two weeks prior to any surgical or dental procedures.
Avoid use in individuals with known allergy to garlic or related Allium species.
Exercise caution in patients with active stomach ulcers or gastrointestinal inflammation.
Consult healthcare provider prior to use during pregnancy or breastfeeding.
Avoid combining multiple forms of garlic simultaneously to prevent overdose.
Monitor for signs of bleeding when coadministered with NSAIDs or blood thinners.
Use with care in pediatric populations; high doses may be harmful to children.
Be vigilant for allergic reactions, particularly when using topical garlic products.
Discontinue use if unexplained bruising, bleeding, or skin reactions occur.
Do not self-treat serious medical conditions with garlic without professional guidance.
Store garlic supplements away from heat, moisture, and light to preserve potency.
Advise patients that garlic supplements are not regulated by FDA and may vary in quality.
Caution in patients using immunosuppressive or antiretroviral therapies due to possible interactions.
Educate patients about the potential for variable efficacy depending on garlic preparation and allicin content.

Warnings

Do not use garlic supplements in place of prescribed medications without professional advice.
Avoid garlic if allergic to garlic or other Allium species due to risk of severe allergic reactions.
Discontinue usage if signs of allergic reaction occur including swelling, hives, or difficulty breathing.
Report any unexpected bleeding, bruising, or delayed clotting to healthcare provider immediately.
Not recommended for children without medical supervision owing to potential toxicity at high doses.
Consult healthcare providers before use if pregnant or breastfeeding to assess risk-benefit ratio.
Avoid use alongside medications that affect blood coagulation without medical consultation.
Herbal supplements may be contaminated with toxic substances; purchase only from reputable sources.
Garlic may interact with numerous medications requiring vigilance and regular medical review.
Stop garlic use at least two weeks prior to elective surgery to decrease bleeding risk.
Avoid crushing or chewing enteric-coated garlic tablets to prevent gastric irritation.
Use caution in patients with digestive disorders or hepatic impairment due to lack of data.
Be aware of possible herbal supplement interactions affecting treatment outcomes.
Regularly review use of garlic supplements in the context of overall therapeutic regimen.
Pregnancy safety not established for medicinal doses; only dietary use considered safe.

Contraindication

Known hypersensitivity or allergy to garlic or related Allium species.
Active bleeding disorders or coagulopathy where anticoagulant effects pose significant risk.
Use in patients taking high doses of blood thinners without strict medical supervision.
Avoid in patients scheduled for surgery or invasive procedures unless discontinued two weeks prior.
Severe gastrointestinal ulceration or inflammation exacerbated by irritant effects of garlic.
Known history of severe anaphylactic reaction to garlic products.
Use contraindicated in patients with a history of severe dermatitis or contact allergy to garlic.
Incompatibility with certain immunosuppressive agents or antiretroviral therapies precluding use.
Avoid use in pediatric patients without explicit medical authorization due to toxicity risk.
Contraindicated in individuals with glucose-6-phosphate dehydrogenase deficiency prone to hemolysis.
Patients with known interactions causing clinically significant adverse effects with garlic.
Use discouraged if inability to comply with dosing and discontinuation recommendations.
Contraindicated when concomitant use with multiple herbal supplements that may cause excessive bleeding.

Drug Interactions

Increased risk of bleeding when combined with anticoagulants such as warfarin, heparin, and antiplatelets like clopidogrel and aspirin.
Potential interaction with NSAIDs (e.g., ibuprofen, naproxen, celecoxib) increasing bleeding tendency.
Decreased effectiveness of certain HIV antiretroviral protease inhibitors including saquinavir and ritonavir due to induced metabolism.
Alteration of cytochrome P450 enzyme activity (notably CYP3A4) may affect metabolism of medications like theophylline, cyclosporine, and chlorzoxazone.
Possible reduction in efficacy of birth control pills due to interaction with hepatic enzymes.
Interaction with acetaminophen metabolism potentially altering hepatotoxicity profiles.
Concomitant use with other herbal supplements affecting coagulation (e.g., ginkgo, ginger, turmeric, horse chestnut) enhances bleeding risk.
May potentiate effects of antihypertensive medications leading to hypotension.
Interaction with drugs that affect platelet function such as ticlopidine, dipyridamole, and urokinase.
Potential interaction with antidepressants and anxiolytics altering their pharmacodynamics.
Interaction with cancer chemotherapeutic agents requires caution due to unknown synergy or antagonism.
Possible interference with diabetes medications necessitating blood glucose monitoring.
Drug interactions may increase or decrease serum drug concentrations necessitating dose adjustments.
Concurrent intake with alcohol may exacerbate gastrointestinal irritation.
Complex interactions with immunosuppressant drugs warrant careful management.

Preparations Of The Drug

Garlic Oil – concentrated garlic essential oil contained in soft gelatin capsules.
Garlic Powder – dehydrated and powdered garlic used in capsules or tablets.
Enteric-Coated Garlic Tablets – designed to prevent stomach irritation and provide delayed release.
Aged Garlic Extract (AGE) – garlic processed to reduce odor and stabilize active compounds.
Deodorized Garlic Preparations – formulated to minimize garlic breath while retaining bioactivities.
Garlic Flakes and Granules – primarily used as dietary supplement or flavoring agents.
Garlic Extract Liquids – tincture or liquid concentrates for oral administration or topical use.
Topical Garlic Preparations – creams or ointments formulated for fungal infections and skin conditions.
Standardized Extracts with specified allicin content to ensure consistent pharmacological activity.
Combination Herbal Formulations including garlic with other botanicals for cardiovascular or immune support.
Powdered Garlic Tablets with enhanced bioavailability technologies.
Capsules containing garlic oil-macerated formulations to optimize absorption.
Fermented Garlic Preparations hypothesized to have increased antioxidant properties.
Microencapsulated Garlic Products designed to reduce odor and improve patient tolerability.
Garlic Blends with vitamins or minerals targeting specific health indications.