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Garlic (Allium sativum)



Interactions

Garlic/Drug Interactions:
  • GeneralGeneral: According to a review, garlic constituents may interfere with the pharmacokinetics (specifically absorption and metabolism) of various agents (331).
  • AbortifacientsAbortifacients: According to secondary sources, garlic may interact with abortifacient agents.
  • AcetaminophenAcetaminophen: Garlic ingestion was associated with a slight increase in sulfate conjugation of acetaminophen in humans (332; 333).
  • AnthelminticsAnthelmintics: According to laboratory research, garlic hexane extract may be effective against the Capillaria species (334). The exact mechanism is not well understood.
  • AntibioticsAntibiotics: In vitro, garlic exerted activity against multiple pathogenic bacteria (335; 336; 87; 337; 338; 237; 339; 340; 341), including Streptococci (342), Mycobacteria (343; 344; 345; 346), and Helicobacter pylori (347; 348; 237; 349).
  • Anticoagulants and antiplateletsAnticoagulants and antiplatelets: According to a case report and comparative study, garlic affects warfarin (350; 351). In theory, the risk of bleeding may be increased by concomitant use of garlic and agents with anticoagulant or antiplatelet effects. Bleeding has been associated with garlic use in several studies and case reports, including intraoperatively, possibly related to impaired platelet aggregation or increased fibrinolysis (88; 89; 90; 91; 92; 93; 94; 95; 96; 35; 97; 98; 99; 100; 101). In humans, garlic affected coagulation time (CT) in a manner similar to clofibrate (103). In contrast, there are several reports of suboptimal quality that suggest a lack of an effect on ex vivo platelet aggregation (242) or bleeding or hemorrhaging in patients on warfarin anticoagulation therapy (323). Additionally, in human research, coadministration of warfarin and garlic did not alter the pharmacokinetics and pharmacodynamics of warfarin (323; 352).
  • AntidiabeticsAntidiabetics: In human research, garlic demonstrated glucose-lowering effects (143; 159; 160; 132), although conflicting evidence exists (149; 124; 127; 100; 148; 161; 162; 106; 150). Animal studies have reported that garlic or its constituents (such as S-allyl cysteine sulfoxide [SACS]) may decrease glucose concentrations and increase insulin secretion (303; 304).
  • AntifungalsAntifungals: In human research, garlic demonstrated antifungal effects (267; 353; 354; 163). In laboratory research, ajoene derived from garlic displayed antifungal activity; however, the mechanism of action is not well understood (355). In laboratory research, allicin enhanced the fungicidal activity of amphotericin B (synergistic effects) (356; 357; 358).
  • Antiglaucoma agentsAntiglaucoma agents: In animal research, S-allylmercaptocysteine, a garlic-derived compound, reduced intraocular pressure and may involve the elevation of ANP levels (48).
  • AntihypertensivesAntihypertensives: Numerous studies have reported small mean reductions in systolic and/or diastolic blood pressure associated with the use of oral garlic vs. placebo, and combination use with antihypertensives may result in additive effects (167; 168; 2; 123; 124; 125; 169; 170; 100; 171; 155; 153; 128; 141; 148; 161; 162; 172; 173; 160; 97; 150; 174; 159; 138; 175; 176; 177; 116; 7; 142; 115; 3; 146; 178; 121; 129; 145; 179), although conflicting evidence exists (2; 180; 181; 145).
  • AntilipemicsAntilipemics: In human research, garlic demonstrated lipid-lowering effects (104; 105; 106; 107; 108; 109; 110; 111; 112; 113; 4; 5; 114; 115; 116; 117; 118; 119; 120; 121; 122; 123; 124; 125; 126; 127; 128; 129; 130; 131; 132), although conflicting and/or mixed evidence exists (133; 134; 135; 136; 3; 2; 137; 138; 139; 140; 141; 142; 358; 143; 144; 145; 146; 147; 148; 35; 149; 150; 151; 152; 153; 154; 155; 156; 157; 158).
  • AntineoplasticsAntineoplastics: In clinical trials, aged garlic extract supplementation has resulted in reduced progression of colorectal adenomas (245; 246).
  • Antiobesity agentsAntiobesity agents: According to animal research, the allyl-containing polysulfides in garlic may increase thermogenesis (42).
  • AntiparasiticsAntiparasitics: The antiparasitic effects of garlic have been reviewed (359). It was indicated that garlic oil has broad-spectrum activity against Trypanosoma, Plasmodium, Giardia, Leishmania, and Cochlospermum planchonii. In animal research, allicin decreased Plasmodium infections (360; 361; 362; 363). In animal research, garlic extract augmented Leishmania engulfment and destroyed amastigotes by macrophages (361). In vitro, ajoene inhibited enzymes found in Trypanosoma (364). Also, in vitro, garlic had antigiardial activity (365).
  • AntiretroviralsAntiretrovirals: Garlic supplementation significantly decreased plasma concentrations of saquinavir taken at a dose of 1,200mg three times daily by 10 healthy volunteers (164; 165; 166). Combination use may result in diminished effects of saquinavir. However, a preliminary study in 10 healthy adults found no significant effects on ritonavir levels following eight doses of 10mg of Natural Source Odourless Garlic® (366).
  • AntiviralsAntivirals: In vitro studies have demonstrated effects against several viruses (367), including influenza B virus, herpes simplex virus type 1 (367), herpes simplex virus type 2, parainfluenza virus type 3, vaccinia virus, vesicular stomatitis virus, human rhinovirus type 2 (23; 24), and cytomegalovirus (37).
  • Cardiovascular agentsCardiovascular agents: Numerous studies have reported small mean reductions in systolic and/or diastolic blood pressure associated with the use of oral garlic vs. placebo (123; 124; 125; 169; 170; 100; 171; 155; 153; 128; 141; 148; 161; 162; 172; 173; 160; 97; 150; 174; 159; 138; 176; 2; 177; 116; 7; 142; 115; 3; 146; 178; 121; 129; 145; 179). Oral ingestion of a large amount of garlic was associated with an acute myocardial infarction in a 23 year-old man with no known history of cardiac disease or known risk factors (275). Chest pain has been reported in humans (179). In a systematic review, two studies reported modest-to-significant reduction of diastolic blood pressure compared to a control group or baseline (134). One study reported a significant decrease of blood pressure compared to the control group.
  • ClofibrateClofibrate: In humans, garlic affected coagulation time (CT) in a manner similar to clofibrate (103).
  • Cytochrome P450-metabolized agentsCytochrome P450-metabolized agents: In human research, garlic oil administration had a lack of CYP2D6 effects (368), although it reduced cytochrome P450 2E1 activity (182; 183). In human research, allicin reduced the metabolism of omeprazole by inhibition of CYP2C19 in individuals with the CYP2C19*1/CYP2C19*1 and CYP2C19*1/CYP2C19*2 or *3 genotypes, but not in those with the CYP2C19*2/ CYP2C19*2 genotype (184). Allicin has been found to reduce the effectiveness of cyclosporine by increasing CYP3A4 activity (185). Although animal and human studies suggest possible induction or inhibition of various P450 enzymes (184; 182; 186; 187), other research has found garlic to have a lack of an effect on the metabolism of CYP450 substrates (alprazolam, P450 3A4 or dextromethorphan, P450 2D6) (188). According to secondary sources, garlic may interact with cytochrome P450 3A4, 3A5, and 3A7 inducers.
  • Dermatologic agentsDermatologic agents : Multiple cases of dermatitis, urticaria, eczema, cheilitis, pruritus, and other dermatologic reactions have been reported in humans (189; 190; 191; 192; 193; 194; 195; 196; 197; 198; 199; 200; 201; 202; 203; 204; 205; 206; 207; 208; 209; 210; 211; 157; 212; 179). Second- and third-degree burns have been reported in children and infants (221; 222; 223; 224; 225) and adults (226; 227; 228; 229; 230; 231; 305; 306; 310; 311).
  • DisulfiramDisulfiram: In theory, the high levels of alcohol found in garlic tinctures may cause nausea or vomiting when taken with disulfiram (Antabuse®).
  • DocetaxelDocetaxel: In human research, garlic lacked a significant effect on docetaxel pharmacokinetics (369). The authors suggested that garlic may decrease docetaxel clearance in subjects with a CYP3A5*1A allele, but further research is warranted.
  • Drugs used for osteoporosisDrugs used for osteoporosis: According to animal research, garlic may suppress bone loss owing to estrogen deficiency (61; 62).
  • EstrogensEstrogens: According to animal research, garlic may have phytoestrogenic activity (63).
  • Fertility agentsFertility agents: According to animal research, chronic garlic ingestion for 70 days may be associated with suppression of spermatogenesis (315).
  • Gastrointestinal agentsGastrointestinal agents: In human research, adverse effects reported included gastrointestinal symptoms (133; 179). Effects of oral dehydrated garlic preparations or raw garlic ingestion may include abdominal pain or fullness, anorexia, diarrhea, flatulence, belching, heartburn, nausea, unpleasant taste, constipation, and bowel obstruction (254; 134; 3; 130; 4; 313; 140; 262; 244; 252; 307; 92).
  • HematologicsHematologics: In theory, the risk of bleeding may be increased by concomitant use of garlic and hematologic agents. Bleeding has been associated with garlic use in several studies and case reports, including intraoperatively, possibly related to impaired platelet aggregation or increased fibrinolysis (88; 89; 90; 91; 92; 93; 94; 95; 96; 35; 97; 98; 99; 100; 101). In contrast, there are several low-quality reports that suggest no effect on ex vivo platelet aggregation (242) or bleeding or hemorrhaging in patients on warfarin anticoagulation therapy (323).
  • HepatotoxinsHepatotoxins: According to human research, administration of intravenous garlic for more than one month may have caused liver damage (163).
  • ImmunosuppressantsImmunosuppressants: According to laboratory and animal research, garlic extract may enhance immune function (370; 371; 372; 373; 374; 375; 376).
  • Intraocular pressure-altering agentsIntraocular pressure-altering agents: In animal research, S-allylmercaptocysteine, a garlic-derived compound, reduced intraocular pressure; it may involve the elevation of ANP levels (48).
  • IsoniazidIsoniazid: In animal research, crude aqueous extract of garlic reduced the maximum concentration and area under the curve (AUC) of garlic; a lack of an effect on half-life was noted (377).
  • MetronidazoleMetronidazole: In theory, the high levels of alcohol found in garlic tinctures may cause nausea or vomiting when taken with metronidazole (Flagyl®).
  • Neurologic agentsNeurologic agents: In animal research, aged garlic extract prevented deterioration of hippocampal-based memory tasks (213) and had antiamyloidogenic effects (13). In vitro, S-allyl-L-cysteine protected against amyloid beta- and tunicamycin-induced neuronal death (214). The protein TRPA1 mediates the response to pungent irritants found in garlic and is found mainly in nociceptive neurons of peripheral ganglia and in all the mechanosensory epithelia of the inner ear (215).
  • Nonsteroidal anti-inflammatory agentsNonsteroidal anti-inflammatory agents: Bleeding has been associated with oral garlic use in several studies and case reports, including intraoperatively, possibly related to impaired platelet aggregation or increased fibrinolysis (88; 87; 91; 92; 93; 94; 90; 95; 96; 35; 97; 98; 99; 100).
  • Performance-enhancing agentsPerformance-enhancing agents: A single administration of garlic resulted in increased endurance performance, likely due to increase in fibrinolytic activity in the resting state (244).
  • Potassium saltsPotassium salts: Garlic is a source of potassium (378). Theoretically, concurrent use of garlic and potassium supplements may increase the risk of hyperkalemia.
  • Renal agentsRenal agents: In human research, administration of intravenous garlic for more than one month caused kidney damage (163).
  • Thyroid hormones iodineThyroid hormones, iodine: Hypothyroidism and reduced iodine uptake by the thyroid have been reported anecdotally with garlic use, which may alter the effects of thyroid agents.
  • VasodilatorsVasodilators: In animal and human research, garlic and its major constituent, allicin, had significant vasodilator activity via hyperpolarization of vascular smooth muscle (216; 217; 218; 219). In animal research, diallyldisulfide and allyl mercaptan, metabolites of allicin, did notpossess this vasodilatory action (219).
  • VasorelaxantsVasorelaxants: In animal and human research, garlic and its major constituent, allicin, had significant vasodilator activity via hyperpolarization of vascular smooth muscle (216; 217; 218; 219). In animal research, diallyldisulfide and allyl mercaptan, metabolites of allicin, did notpossess this vasodilatory action (219).
  • Weight loss agentsWeight loss agents: Weight loss has been a reported side effect following intravenous Allium sativum extract (302; 163).

Garlic/Herb/Supplement Interactions:
  • GeneralGeneral: According to a review, garlic constituents may interfere with the pharmacokinetics (specifically absorption and metabolism) of various agents (331).
  • AbortifacientsAbortifacients: According to secondary sources, garlic may interact with abortifacient herbs and supplements.
  • AnthelminticsAnthelmintics: According to laboratory research, garlic hexane extract may be effective against the Capillaria species (334). The exact mechanism is not well understood.
  • AntibacterialsAntibacterials: In vitro, garlic exerted activity against multiple pathogenic bacteria (335; 336; 87; 337; 338; 237; 339; 340; 341), including Streptococci (342), Mycobacteria (343; 344; 345; 346) and Helicobacter pylori (347; 348; 237; 349).
  • Anticoagulants and antiplateletsAnticoagulants and antiplatelets: In theory, the risk of bleeding may be increased by concomitant use of garlic and agents with anticoagulant or antiplatelet effects. Bleeding has been associated with garlic use in several studies and case reports, including intraoperatively, possibly related to impaired platelet aggregation or increased fibrinolysis (88; 89; 90; 91; 92; 93; 94; 95; 96; 35; 97; 98; 99; 100; 101). In humans, garlic affected coagulation time (CT) in a manner similar to clofibrate (103). In contrast, there are several reports of suboptimal quality that suggest a lack of an effect on ex vivo platelet aggregation (242) or bleeding or hemorrhaging in patients on warfarin anticoagulation therapy (323). Additionally, in human research, coadministration of warfarin and garlic did not alter the pharmacokinetics and pharmacodynamics of warfarin (323; 352).
  • AntifungalsAntifungals: In human research, garlic has demonstrated antifungal effects (267; 353; 354; 163). In laboratory research, ajoene derived from garlic displayed antifungal activity; however, the mechanism of action is not well understood (355). In laboratory research, allicin enhanced the fungicidal activity of amphotericin B (synergistic effects) (356; 357; 358). Theoretically, concurrent use may modulate the effectiveness of antifungals.
  • Antiglaucoma agentsAntiglaucoma agents: In animal research, S-allylmercaptocysteine, a garlic-derived compound, reduced intraocular pressure; it may involve the elevation of ANP levels (48).
  • AntilipemicsAntilipemics: In human research, garlic demonstrated lipid-lowering effects (104; 105; 106; 107; 108; 109; 110; 111; 112; 113; 4; 5; 114; 115; 116; 117; 118; 119; 120; 121; 122; 123; 124; 125; 126; 127; 128; 129; 130; 131; 132), although conflicting and/or mixed evidence exists (133; 134; 135; 136; 3; 2; 137; 138; 139; 140; 141; 142; 358; 143; 144; 145; 146; 147; 148; 35; 149; 150; 151; 152; 153; 154; 155; 156; 157; 158).
  • AntineoplasticsAntineoplastics: In clinical trials, aged garlic extract supplementation has resulted in reduced progression of colorectal adenomas (245; 246).
  • Antiobesity agentsAntiobesity agents: According to animal research, the allyl-containing polysulfides in garlic may increase thermogenesis (42).
  • AntioxidantsAntioxidants: In various studies, garlic and its constituents displayed antioxidant activity: increasing activities of antioxidant enzymes (glutathione peroxidase, catalase, and superoxide dismutase), lowering xanthine oxidase activity (i.e., eliminating oxidant stress), and inhibiting lipid peroxidation and prostaglandin production (379; 380; 381; 382; 383; 384; 385; 30; 39; 386; 387; 388; 389; 390; 391; 392; 393; 394; 395; 396; 397; 398; 399; 27; 400).
  • AntiparasiticsAntiparasitics: The antiparasitic effects of garlic have been reviewed (359). It was indicated that garlic oil has broad-spectrum activity against Trypanosoma, Plasmodium, Giardia, Leishmania, and Cochlospermum planchonii. In animal models, allicin decreased Plasmodium infections (360; 361; 362; 363). In animal research, garlic extract augmented Leishmania engulfment and destroyed amastigotes by macrophages (361). In vitro, ajoene inhibited enzymes found in Trypanosoma (364). Also, in vitro, garlic had antigiardial activity (365).
  • AntiviralsAntivirals: In vitro studies have demonstrated effects against several viruses (367), including influenza B virus, herpes simplex virus type 1 (367), herpes simplex virus type 2, parainfluenza virus type 3, vaccinia virus, vesicular stomatitis virus, human rhinovirus type 2 (23; 24), and cytomegalovirus (37).
  • Cardiovascular agentsCardiovascular agents: Numerous studies have reported small mean reductions in systolic and/or diastolic blood pressure associated with the use of oral garlic vs. placebo (123; 124; 125; 169; 170; 100; 171; 155; 153; 128; 141; 148; 161; 162; 172; 173; 160; 97; 150; 174; 159; 138; 176; 2; 177; 116; 7; 142; 115; 3; 146; 178; 121; 129; 145; 179). Oral ingestion of a large amount of garlic was associated with an acute myocardial infarction in a 23 year-old man with no known history of cardiac disease or known risk factors (275). Chest pain has been reported in humans (179). In a systematic review, two studies reported modest-to-significant reduction of diastolic blood pressure compared to a control group or baseline (134). One study reported a significant decrease of blood pressure compared to the control group.
  • Cytochrome P450-modifying agentsCytochrome P450-modifying agents: In human research, garlic oil reduced cytochrome P450 2E1 activity (182; 183). In human research, allicin reduced the metabolism of omeprazole by inhibition of CYP2C19 in individuals with the CYP2C19*1/CYP2C19*1 and CYP2C19*1/CYP2C19*2 or *3 genotypes, but not in those with the CYP2C19*2/ CYP2C19*2 genotype (184). Allicin has been found to reduce the effectiveness of cyclosporine by increasing CYP3A4 activity (185). Although animal and human research suggests a possible induction or inhibition of various P450 enzymes (184; 182; 186; 187), other research has found garlic to have a lack of an effect on the metabolism of CYP450 substrates (alprazolam, P450 3A4 or dextromethorphan, P450 2D6) (188). According to secondary sources, garlic may interact with cytochrome P450 3A4, 3A5, and 3A7 inducers.
  • Dermatologic agentsDermatologic agents: Multiple cases of dermatitis, urticaria, eczema, cheilitis, pruritus, and other dermatologic reactions have been reported in humans (189; 190; 191; 192; 193; 194; 195; 196; 197; 198; 199; 200; 201; 202; 203; 204; 205; 206; 207; 208; 209; 210; 211; 157; 212; 179). Second- and third-degree burns have been reported in children and infants (221; 222; 223; 224; 225) and adults (226; 227; 228; 229; 230; 231; 305; 306; 310; 311).
  • Fertility agentsFertility agents: In animal research, chronic garlic ingestion for 70 days may be associated with suppression of spermatogenesis (315).
  • Fish oil, EPA (eicosapentaenoic acid)Fish oil, EPA (eicosapentaenoic acid): EPA is found in deep-sea fish oils. Garlic may potentiate antithrombotic effects of EPA, and theoretically, concomitant use of these agents may increase the risk of bleeding. Garlic and fish oil may have additive lipid-lowering effects. In humans, the combination of fish oil and garlic resulted in a reduction of total cholesterol and LDL cholesterol by 20% and 21%, respectively (102).
  • GinkgoGinkgo: Ginkgo may potentiate garlic's increased bleeding risk (according to secondary sources). Caution is warranted.
  • Gastrointestinal agentsGastrointestinal agents: In human research, adverse effects reported included gastrointestinal symptoms (133; 179). Effects of oral dehydrated garlic preparations or raw garlic ingestion may include abdominal pain or fullness, anorexia, diarrhea, flatulence, belching, heartburn, nausea, unpleasant taste, constipation, and bowel obstruction (254; 134; 3; 130; 4; 313; 140; 262; 244; 252; 307; 92).
  • HematologicsHematologics: In theory, the risk of bleeding may be increased by concomitant use of garlic and hematologic agents. Bleeding has been associated with garlic use in several studies and case reports, including intraoperatively, possibly related to impaired platelet aggregation or increased fibrinolysis (88; 89; 90; 91; 92; 93; 94; 95; 96; 35; 97; 98; 99; 100; 101). In contrast, there are several low-quality reports that suggest a lack of an effect on ex vivo platelet aggregation (242) or bleeding or hemorrhaging in patients on warfarin anticoagulation therapy (323). Additionally, in human research, coadministration of warfarin and garlic did not alter the pharmacokinetics and pharmacodynamics of warfarin (323; 352).
  • HepatotoxinsHepatotoxins: In human research, administration of intravenous garlic for more than one month may have caused liver damage (163).
  • HypoglycemicsHypoglycemics: In human research, garlic demonstrated glucose-lowering effects (143; 159; 160; 132), although conflicting evidence exists (149; 124; 127; 100; 148; 161; 162; 106; 150). Animal studies have reported that garlic or its constituents (such as S-allyl cysteine sulfoxide [SACS]) may decrease glucose concentrations and increase insulin secretion (303; 304),
  • HypotensivesHypotensives: Numerous studies have reported small mean reductions in systolic and/or diastolic blood pressure associated with the use of oral garlic vs. placebo, and combination use with antihypertensives may result in additive effects (167; 168; 2; 123; 124; 125; 169; 170; 100; 171; 155; 153; 128; 141; 148; 161; 162; 172; 173; 160; 97; 150; 174; 159; 138; 175; 176; 177; 116; 7; 142; 115; 3; 146; 178; 121; 129; 145; 179), although conflicting evidence exists (2; 180; 181; 145). In a systematic review, two studies reported modest to significant reduction of diastolic blood pressure compared to a control group or baseline (134). One study reported a significant decrease of blood pressure compared to the control group.
  • ImmunosuppressantsImmunosuppressants: According to laboratory and animal research, garlic extract may enhance immune function (370; 371; 372; 373; 374; 375; 376).
  • Intraocular pressure-altering agentsIntraocular pressure-altering agents: In animal research, S-allylmercaptocysteine, a garlic-derived compound, reduced intraocular pressure and may involve the elevation of ANP levels (48).
  • Neurologic agentsNeurologic agents: In animal research, aged garlic extract prevented deterioration of hippocampal-based memory tasks (213) and had antiamyloidogenic effects (13). In vitro, S-allyl-L-cysteine protected against amyloid beta- and tunicamycin-induced neuronal death (214). The protein TRPA1 mediates the response to pungent irritants found in garlic and is found mainly in nociceptive neurons of peripheral ganglia and in all the mechanosensory epithelia of the inner ear (215).
  • Osteoporosis agentsOsteoporosis agents: According to animal research, garlic may suppress bone loss owing to estrogen deficiency (61; 62).
  • Performance-enhancing agentsPerformance-enhancing agents: Single administration of garlic resulted in increased endurance performance, likely due to increase in fibrinolytic activity in the resting state (244).
  • PhytoestrogensPhytoestrogens: According to animal research, garlic may have phytoestrogenic activity (63).
  • PotassiumPotassium: Garlic is a source of potassium (378) and may elevate potassium levels. Theoretically, concurrent use of garlic and potassium supplements may increase the risk of hyperkalemia.
  • Pycnogenol®Pycnogenol®: Garlic and Pycnogenol® increased human growth hormone secretion in laboratory experiments (401).
  • Renal agentsRenal agents: In human research, administration of intravenous garlic for more than one month caused kidney damage (163).
  • SeleniumSelenium: Garlic has been found to contain selenium in various studies (402; 403; 404). Garlic supplementation may increase amounts of selenium in the body.
  • Thyroid agentsThyroid agents: Hypothyroidism and reduced iodine uptake by the thyroid following garlic intake have been reported anecdotally.
  • VasodilatorsVasodilators: In animal and human research, garlic and its major constituent, allicin, had significant vasodilator activity via hyperpolarization of vascular smooth muscle (216; 217; 218; 219). In animal research, diallyldisulfide and allyl mercaptan, metabolites of allicin, did notpossess this vasodilatory action (219).
  • ZincZinc: In animal research, a complex of zinc and garlic-derived allixin exhibited high insulin-mimetic and hypoglycemic activity (405).
  • Weight loss agentsWeight loss agents: Weight loss has been a reported side effect following intravenous Allium sativum extract (302; 163).

Garlic/Food Interactions:
  • ButterButter: Garlic oil prevented a fall in fibrinolytic activity due to increased butter consumption (406).
  • OnionOnion: A combination of garlic and onion may lower cholesterol in humans (407).

Garlic/Lab Interactions:
  • Arterial oxygenArterial oxygen: In humans, there was significant improvement in arterial oxygen levels in the garlic group compared to placebo, with an increase of 24.66% vs. 7.37% after nine months of treatment (p<0.001) (251). There was significant decrease in alveolar-arterial oxygen gradient in the garlic group vs. placebo group after nine months (28.35% vs. 10.73%, respectively, p<0.001).
  • Blood fibrinolytic activityBlood fibrinolytic activity: In humans, garlic and onion mitigated postprandial blood fibrinolytic activity decreases (103).
  • Blood glucoseBlood glucose: In humans, garlic has demonstrated glucose-lowering effects (143; 159; 160; 132), although conflicting evidence exists (149; 124; 127; 100; 148; 161; 162; 106; 150). Animal studies have reported that garlic or its constituents (such as S-allyl cysteine sulfoxide [SACS]) may decrease glucose concentrations and increase insulin secretion (303; 304),
  • Blood pressureBlood pressure: Numerous studies have reported small mean reductions in systolic and/or diastolic blood pressure associated with the use of oral garlic vs. placebo, and combination use with antihypertensives may result in additive effects (167; 168; 2; 123; 124; 125; 169; 170; 100; 171; 155; 153; 128; 141; 148; 161; 162; 172; 173; 160; 97; 150; 174; 159; 138; 175; 176; 177; 116; 7; 142; 115; 3; 146; 178; 121; 129; 145), although conflicting evidence exists (2; 180; 181; 145; 179). In a systematic review, two studies reported modest to significant reduction of diastolic blood pressure compared to a control group or baseline (134). One study reported a significant decrease of blood pressure compared to the control group.
  • Coagulation panelCoagulation panel: In humans, a significant decrease in coagulation time was noted (134). An increase in a previously stabilized internationalized ratio (INR) with concomitant garlic and warfarin (Coumadin®) use has been reported, which has been subsequently debated due to limited clinical information (321; 91). However, in a small controlled study, no significant change in INR values was found in a group of patients stabilized on warfarin therapy (INR target 2-3) who were started on 1,200mg of aged garlic extract for two months, compared to a placebo group. Clinical outcomes such as increased bleeding were not assessed, and the study was likely too small and brief to significantly measure such outcomes (322). In humans, garlic affected coagulation time (CT) in a manner similar to clofibrate (103).
  • Creatine kinaseCreatine kinase: In humans, allicin supplementation resulted in reduced exercise-induced plasma creatine kinase (CK), muscle-specific creatine kinase (CK-MM), interleukin-6 (IL-6), and perceived muscle soreness after exercise when compared to placebo (243).
  • EndothelinEndothelin: In humans, garlic modulated plasma endothelin (108)
  • EstrogensEstrogens: According to animal research, garlic may have phytoestrogenic activity (63) and may increase estrogen levels.
  • FolateFolate: In human research, garlic supplementation increased folate levels (408).
  • Heinz bodiesHeinz bodies: In humans, the number of Heinz bodies decreased after garlic ingestion (58.9 ± 20.0% at baseline to 29.8 ± 15.3% at follow-up; p=0.03) (264).
  • Homocysteine levelsHomocysteine levels: According to secondary information, garlic may lower homocysteine levels in the blood.
  • Lipid profileLipid profile: In humans, garlic has demonstrated lipid-lowering effects (104; 105; 106; 107; 108; 109; 110; 111; 112; 113; 4; 5; 114; 115; 116; 117; 118; 119; 120; 121; 122; 123; 124; 125; 126; 127; 128; 129; 130; 131; 132), although conflicting and/or mixed evidence exists (133; 134; 135; 136; 3; 2; 137; 138; 139; 140; 141; 142; 401; 143; 144; 145; 146; 147; 148; 35; 149; 150; 151; 152; 153; 154; 155; 156; 157; 158).
  • Liver-function tests (LFTs)Liver-function tests (LFTs): In animal research, garlic elevated the activity of gamma-glutamate transpeptidase (GGT), glutathione S-transferase (GST), 5'-nucleotidase, alkaline phosphatase (ALP), aspartate transaminase (AST), and alanine transaminase (ALT) (409).
  • Plasma fibrinogenPlasma fibrinogen: In human research, garlic significantly decreased plasma fibrinogen (134).
  • PotassiumPotassium: Garlic is a source of potassium (378) and may elevate potassium levels.
  • Urine allylmercapturic acidUrine allylmercapturic acid: Garlic tablets and fresh garlic may result in urinary excretion of allylmercapturic acid (N-acetyl-S-allyl-L-cysteine), which may interfere with urinary monitoring of workers for industrial exposure to allyl halides (410).
  • VO2maxVO2max: In humans, VO2max and mean endurance performance time for treadmill running increased significantly five hours after the ingestion of a single dose of garlic compared to placebo (p<0.01 and p<0.001, respectively) (244).

Copyright © 2011 Natural Standard (www.naturalstandard.com)


The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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