Herb-Drug Interactions: Garlic

Contents

Allium sativum L. (Alliaceae)

Synonym(s) and related species

Ajo, Allium.

Pharmacopoeias

Garlic (US Ph 32); Garlic Delayed Release Tablets (US Ph 32); Garlic Fluid Extract (US Ph 32); Garlic for Homeopathic Preparations (British Ph 2009, European Ph 2008); Garlic Powder (European Ph, 6th ed., 2008 and Supplements 6.1, 6.2, 6.3 and 6.4, British Pharmacopoeia 2009); Powdered Garlic (US Ph 32); Powdered Garlic Extract (The United States Ph 32).

Constituents

Garlic products are produced from the bulbs (cloves) of garlic and are usually standardised according to the content of the sulphur-containing compounds, alliin, allicin (produced by the action of the enzyme alliinase on alliin) and/or γ-glutamyl-(S)-allyl-L-cysteine.

Other sulphur compounds such as allylmethyltrisulfide. allylpropyldisulfide, diallyldisulfide, diallyltrisulfide, ajoene and vinyldithiines, and mercaptan are also present. Garlic also contains various glycosides, monoterpenoids, enzymes, vitamins, minerals and flavonoids based on kaempferol and quercetin.

Use and indications

Garlic has been used to treat respiratory infections (such as colds, flu, chronic bronchitis, and nasal and throat catarrh) and cardiovascular disorders. It is believed to possess antihypertensive, antithrombotic, fibrinolytic, antimicrobial, anticancer, expectorant, antidiabetic and lipid-lowering properties.

It is also used extensively as an ingredient in foods.

Pharmacokinetics

There are many active constituents in garlic and their roles have not been fully elucidated. Allicin is subject to a considerable first-pass effect and passes through the liver unmetabolised only at high concentrations, but it is a very unstable compound and, as with ajoene, the vinyldithiins and diallylsulfide, it is not found in blood or urine after oral ingestion.

There have been several experimental studies undertaken to assess the effects garlic and its constituents have on cytochrome P450 isoenzymes. In vitro studies suggest that garlic inhibits, to varying degrees: CYP2C9, CYP2C19, the CYP3A isoenzyme subfamily, CYP2A6,5 CYP1A2,CYP2D6 and CYP2E1. Studies in rats suggest that garlic inhibits CYP2E1, and induces CYP2C9*2. However, in clinical studies, garlic and its constituents seem unlikely to affect the cytochrome P450 isoenzymes to a clinically relevant extent, see benzodiazepines, for CYP3A4, caffeine, for CYP1A2, and dextromethorphan, for CYP2D6. The possible exception to the lack of effect of garlic on cytochrome P450 is CYP2E1, which requires further study, see chlorzoxazone, and paracetamol (acetaminophen).

Any effect on the drug transporter P-glycoprotein, shown in vitro, is also unlikely to be clinically significant, see protease inhibitors.

For information on the pharmacokinetics of individual flavonoids present in garlic, see under flavonoids.

Interactions overview

Case reports suggest that garlic may have additive blood pressure-lowering effects with lisinopril, and may cause bleeding in those taking warfarin or fluindione. It has also been suggested that any antiplatelet effects of garlic may be additive with conventional antiplatelet drugs and NSAIDs, and studies suggest that garlic may reduce isoniazid levels. However, no interaction has been proven with any of these drugs.

In general, garlic seems to have no effect, or have only clinically irrelevant effects when it is given with alcohol, benzodiazepines (such as midazolam), caffeine, chlorzoxazone, dextromethorphan, docetaxel, gentamicin, paracetamol (acetaminophen), rifampicin (rifampin) or ritonavir. Any interaction between garlic and fish oils may be beneficial.

One study suggested that a high-fat diet did not affect the absorption of some of the active constituents of garlic oil. For information on the interactions of individual flavonoids present in garlic, see under flavonoids.

Garlic + ACE inhibitors

In a single report, a patient taking lisinopril developed marked hypotension and became faint after taking garlic capsules.

Evidence, mechanism, importance and management

A man whose blood pressure was 135/90 mmHg while taking lisinopril 15mg daily began to take garlic 4mg daily (Boots odourless garlic oil capsules). After 3 days he became faint on standing and was found to have a blood pressure of 90/60 mmHg. Stopping the garlic restored his blood pressure to 135/90 mmHg within a week. The garlic on its own did not lower his blood pressure. The reasons for this interaction are not known, although garlic has been reported to cause vasodilation and blood pressure reduction. This seems to be the first and only report of this reaction, so its general importance is small. There seems to be nothing documented about garlic and any of the other ACE inhibitors.

Garlic + Alcohol

The interaction between garlic and alcohol is based on experimental evidence only.

Evidence, mechanism, importance and management

Garlic juice, from fresh garlic bulbs, inhibited the metabolism of alcohol in mice. Garlic is a common ingredient in food and so it is very unlikely that this interaction is clinically relevant.

Garlic + Antiplatelet drugs

Garlic may have antiplatelet properties. It might therefore be expected to increase the risk of bleeding with conventional antiplatelet drugs and other drugs that have antiplatelet adverse effects.

Clinical evidence

In a study in 23 healthy subjects, liquid aged garlic extract 5mL (Kyolic), given daily for 13 weeks, inhibited both the rate of platelet aggregation and total platelet aggregation. Similar effects were found in another study in 28 healthy subjects given aged garlic extract capsules 2.4 g, 4.8 g and 7.2 g. Each dose was given daily for a 6-week period.

Experimental evidence

Ajoene, a sulphur compound derived from garlic with antiplatelet and antithrombotic properties, was found to synergistically potentiate the antiplatelet actions of dipyridamole, epoprostenol and indometacin in vitro.

Mechanism

Uncertain. The authors of an experimental study suggest that ajoene inhibits the binding of fibrinogen to the fibrinogen receptor, which occurs in the final step of the platelet aggregation pathway. Ajoene would therefore be expected to interact synergistically with antiplatelet drugs that act at an earlier step in the pathway.

Importance and management

There is a reasonable body of evidence, which suggests that aged garlic herbal products may have antiplatelet properties. If they do, and they are similarly active to low-dose aspirin, they might therefore be expected to increase the risk of bleeding with conventional antiplatelet drugs and other drugs that have antiplatelet adverse effects, such as indometacin. However, considering the widespread use of garlic and garlic products, and the limited information available, it seems unlikely that garlic has any generally important interaction with antiplatelet drugs. Nevertheless, bear the possibility in mind in the event of an unexpected response to treatment.

Garlic + Benzodiazepines

Garlic does not appear to affect the pharmacokinetics of alprazolam, midazolam or triazolam to a clinically relevant extent

Clinical evidence

A study in 14 healthy subjects found that Kwai garlic tablets 600 mg twice daily for 14 days did not affect the pharmacokinetics of a single 2-mg dose of alprazolam.

Similarly, garlic oil 500 mg three times daily for 28 days did not affect the metabolism of midazolam 8mg in young or elderlyhealthy subjects.

Experimental evidence

The effect of garlic constituents; alliin, cycloalliin, methylin, S-methyl-L-cysteine, S-allyl-L-cysteine, N-acetyl-S-allyl-L-cysteine, S-allomercapto-L-cysteine, and γ-glutamyl-S-allyl-L-cysteine, on the activity of the CYP3A probe substrate, triazolam, was investigated using human liver microsomes. Both S-methyl-L-cysteine and S-allyl-L-cysteine inhibited the activity of CYP3A, with the latter reducing its activity by about 60%. No other significant inhibition was apparent.

Mechanism

The findings of the clinical studies suggest that garlic does not have a clinically relevant effect on CYP3A4 activity. Although some inhibition of CYP3A was seen in the in vitro study, it was not considered to be mechanism based and the concentrations used were an order of magnitude greater than the anticipated in vivo concentrations.

Importance and management

The results of the clinical studies suggest that garlic does not affect the metabolism of alprazolam or midazolam, and therefore no dosage adjustments would be expected to be necessary if patients taking these benzodiazepines also take garlic supplements.

Midazolam is used as a probe drug for CYP3A4 activity, and therefore these results also suggest that a pharmacokinetic interaction between garlic and other CYP3A4 substrates is unlikely.

Garlic + Caffeine

Garlic does not appear to affect the pharmacokinetics of caffeine.

Clinical evidence

Garlic oil 500 mg three times daily for 28 days did not affect the metabolism of a single 100-mg dose of caffeine in young or elderlyhealthy subjects.

Experimental evidence

No relevant data found.

Mechanism

Garlic does not have a clinically relevant effect on the cytochrome P450 isoenzyme CYP1A2 activity using caffeine as a probe substrate.

Importance and management

Evidence for an interaction between garlic and caffeine appears to come from two well-designed studies in humans. These studies suggest that garlic does not affect the metabolism of caffeine, and therefore an increase in caffeine adverse effects would not be expected in those who also take garlic supplements. Caffeine is used as a probe drug for CYP1A2 activity, and therefore these results also suggest that a pharmacokinetic interaction between garlic and other CYP1A2 substrates is unlikely.

Garlic + Chlorzoxazone

The metabolism of chlorzoxazone is modestly inhibited by garlic but this effect is probably not clinically relevant.

Clinical evidence

Garlic oil 500 mg, given to 12 healthy subjects three times daily for 28 days, reduced the conversion of a single 500-mg dose of chlorzoxazone to 6-hydroxychlorzoxazone by about 40%.! In a later similar study by the same authors, in 12 elderly healthy subjects, a smaller reduction of 22% was seen.

Another study in 8 healthy subjects found that a high dose of the garlic constituent diallyl sulfide 200 micrograms/kg (equivalent to 15 cloves of fresh garlic, containing 1 mg/g diallyl sulfide), reduced the conversion of chlorzoxazone to 6-hydroxychlorzoxazone by about 30%.3

Experimental evidence

A garlic constituent, diallyl sulfide 50mg/kg and 200mg/kg, was given to rats 12 hours before an intravenous dose ofchlorzoxazone 150 micromols/kg. Diallyl sulfide increased the AUC of chlorzoxazone by threefold and fivefold, respectively.

Mechanism

Garlic appears to inhibit the activity of the cytochrome P450 isoenzyme CYP2E1, which metabolises chlorzoxazone to 6-hydroxychlorzoxazone.

Importance and management

There appear to be several clinical studies into the potential for an interaction between garlic and chlorzoxazone. Although these studies suggest that metabolism of chlorzoxazone is modestly inhibited by garlic in healthy subjects, this effect is probably not clinically relevant.

Chlorzoxazone is used as a probe drug for CYP1E2 activity, and therefore these results also suggest that a pharmacokinetic interaction between garlic and other CYP1E2 substrates is unlikely.

Garlic + Dextromethorphan

Garlic does not appear to affect the pharmacokinetics of dextromethorphan or debrisoquine.

Clinical evidence

A study in 14 healthy subjects found that Kwai garlic tablets 600 mg twice daily for 14 days did not affect the pharmacokinetics of a single 30-mg dose of dextromethorphan.

Garlic oil 500 mg three times daily for 28 days did not affect the metabolism of debrisoquine 5mg in young or elderly healthy subjects.

Experimental evidence

The effect of garlic constituents; alliin, cycloalliin, methylin, S-methyl-L-cysteine, S-allyl-L-cysteine, N-acetyl-S-allyl-L-cysteine, S-allomercapto-L-cysteine, and γ-glutamyl-S-allyl-L-cysteine, on the activity of the CYP2D6 probe substrate, dextromethorphan, was investigated using human liver microsomes. No significant inhibition was apparent.

Mechanism

Garlic does not appear to affect the cytochrome P450 isoenzyme CYP2D6.

Importance and management

There appear to be two clinical studies investigating the potential for an interaction between garlic and dextromethorphan, both of which found that the pharmacokinetics of dextromethorphan were unaffected by garlic and its constituents. Therefore the dosage of dextromethorphan would not need adjusting if patients also wish to take garlic supplements.

Dextromethorphan and debrisoquine are used as probe drugs for CYP2D6 activity, and therefore these results also suggest that a pharmacokinetic interaction between garlic and other CYP2D6 substrates is unlikely.

Garlic + Docetaxel

Garlic does not appear to affect the pharmacokinetics of intravenous docetaxel.

Clinical evidence

In a pharmacokinetic study, 10 patients with metastatic, or incurable localised, breast cancer were given 1-hour intravenous infusions of docetaxel 30mg/m weekly for 3 weeks (days 1, 8 and 15). Five days after the first infusion, garlic tablets 600 mg were taken twice daily for 13 days (days 5 to 17). The garlic tablets used were GarliPure Maximum Allicin Formula, Natrol, containing 3.6mg of allicin per tablet. Patients were also given a premedication regimen of oral dexamethasone 8mg 12 hours before each docetaxel infusion and then every 12 hours for two more doses, and ondansetron 8mg, ranitidine 150mg and diphenhydramine 25 mg half an hour before each infusion of docetaxel. Garlic tablets had no effect on the pharmacokinetics of docetaxel on the second or third week, when compared with the first week (i.e. after 4 and 12 days’ use of garlic).

Experimental evidence

No relevant data found.

Mechanism

Docetaxel is metabolised, in part, by the cytochrome P450 isoenzyme CYP3A4. This study suggests that garlic is unlikely to alter the activity of this isoenzyme. See also benzodiazepines.

Importance and management

Evidence appears to be limited to this one study, but it is supported by the findings of other studies that suggest that garlic does not alter the effects of CYP3A4, the main route of docetaxel metabolism. Therefore what is known suggests that no pharmacokinetic interaction would be expected in patients taking garlic supplements with intravenous docetaxel.

Garlic + Food

The information regarding the use of garlic with food is based on experimental evidence only.

Evidence, mechanism, importance and management

In a study in rats that were fed a high-fat or low-fat diet, and also given garlic oil or its constituents diallyl sulfide and diallyl disulfide, there were no biochemical changes between the groups attributable to an interaction between the garlic oil and dietary fat. No clinical interaction is expected; note that garlic is extensively used as a food ingredient.

For the lack of pharmacokinetic interaction of garlic with caffeine, see caffeine.

Garlic + Gentamicin

The information regarding the use of garlic with gentamicin is based on experimental evidence only.

Evidence, mechanism, importance and management

Aged garlic extract or garlic powder extract did not affect the in vitro antibacterial activity of gentamicin 2.6 micrograms/L and 2.7 micrograms/L on Escherichia coli. The bactericidal effect of gentamicin against E. coli, measured by optical density, was increased by S-allylcysteine, diallyl sulfide, and diallyl disulfide, at concentrations of 0.25mg/mL, 0.5mg/mL and lmg/mL but the significance of this is unclear. However, no clinically significant interaction is expected as far as antibacterial activity is concerned.

Garlic + Herbal medicines; Caffeine-containing

Garlic did not interact with caffeine, and is therefore unlikely to interact with caffeine-containing herbs, as a result of this constituent.

Garlic + Herbal medicines; Fish oil

Garlic supplements and fish oils may have beneficial effects on blood lipids.

Clinical evidence

In a placebo-controlled study in 46 subjects with moderate, untreated hypercholesterolaemia, combined use of garlic pills 300 mg three times daily (Kwai) and fish oil capsules 4g three times daily for 12 weeks was compared with either garlic or fish oil alone. Garlic modestly reduced total cholesterol, and fish oil did not alter this effect. Fish oil reduced triacylglycerol levels, and garlic did not alter this effect. Garlic alone reduced low-density-lipoprotein cholesterol, and combined use with fish oil reversed the increase of low-density-lipoprotein cholesterol seen with fish oil alone and produced a reduction similar to that seen with garlic alone. Slight reductions in blood pressure were also reported with all treatments. The fish oil used was 1-g capsules (Nupulse) each containing eicosapentaenoic acid 180 mg and docosahexaenoic acid 120 mg.

Experimental evidence

Garlic oil has been found to enhance the antioxidant effects of fish oils in rats.

Mechanism

Unclear. In the experimental study, garlic oil synergistically increased the induction of the antioxidant superoxide dismutase by fish oils, and the combination additively increased the protein levels of CYP1A1, CYP2E1 and CYP3A1.

Importance and management

The available clinical evidence appears to come from one study, which suggests that the combined use of garlic supplements and fish oils may have beneficial effects on blood lipids, which are known to be risk factors in coronary artery disease and atherosclerosis. While the clinical importance is inconclusive, any interaction is not expected to be harmful as far as blood lipids are concerned. Further study is needed to establish the benefits of combined use.

Garlic + Isoniazid

The interaction between garlic and isoniazid is based on experimental evidence only.

Clinical evidence

No interactions found.

Experimental evidence

In a study in rabbits, a garlic extract, produced from blended garlic cloves (exact dosage unknown) and given orally over 14 days, reduced the AUC and maximum serum levels of a single 30-mg/kg dose of isoniazid by about 55% and 65%, respectively, when compared with the levels attained after a single 30-mg/kg dose of isoniazid given 7 days before the garlic extract.

Mechanism

Unclear. It was anticipated that garlic might increase isoniazid levels by inhibiting the cytochrome P450 isoenzyme CYP2E1, but decreased levels were seen. While the authors speculate that garlic extract may induce enzymes in the intestinal mucosa, which interferes with the absorption of isoniazid, they suggest that the findings cannot be explained solely on this basis.

Importance and management

The evidence is limited to this one study, and because the mechanism is unknown, a crude garlic extract was used, and the data are from rabbits, it is difficult to apply these findings to a clinical setting. However, if the reduction was shown to be replicated in humans then isoniazid efficacy might be reduced, so further study is warranted. Until more is known, a conservative approach would be to suggest some caution with the use of garlic supplements in patients taking isoniazid.

Garlic + Paracetamol (Acetaminophen)

Studies in healthy subjects found that garlic did not affect the pharmacokinetics of single-dose paracetamol to a clinically relevant extent

Clinical evidence

A study in 16 healthy subjects found that the use of an aged garlic extract (approximately equivalent to 6 to 7 cloves of garlic daily) for 3 months had little effect on the metabolism of a single 1-g oral dose of paracetamol.

Experimental evidence

Diallyl sulfide, a constituent of garlic, and, to a greater extent, its metabolite diallyl sulfone, protected mice from paracetamol-induced hepatotoxicity when given immediately after a toxic dose of paracetamol (200mg/kg). The effect of diallyl sulfone 25mg/kg was equivalent to that of the known antidote, acetylcysteine.

Mechanism

There was a very slight increase in glucuronidation of a therapeutic dose of paracetamol after the long-term use of garlic in the clinical study, and some evidence that sulfate conjugation was enhanced, but no effect on oxidative metabolism.

It was suggested that diallyl sulfone protected against the hepatotoxicity of paracetamol after a toxic dose in mice because it irreversibly inhibited the cytochrome P450 isoenzyme CYP2E1. This isoenzyme is thought to be responsible for the production of a minor but highly reactive paracetamol metabolite, N-acetyl-p-benzoquinoneimine (NABQI).

Importance and management

The evidence regarding an interaction between paracetamol and garlic is limited, but what is known suggests that no clinically significant interaction would be expected if paracetamol is taken with garlic. The animal data suggest that it is possible that some garlic constituents, or substances derived from them, might prove to protect against the hepatotoxicity from higher than therapeutic doses of paracetamol, but this requires further study.

Garlic + Protease inhibitors

A garlic supplement reduced the plasma levels of saquinavir in one study, but had little effect in another. Another garlic supplement did not significantly affect the pharmacokinetics of a single dose of ritonavir.

Clinical evidence

In a study in 9 healthy subjects garlic reduced the AUC and maximum and minimum plasma levels of saquinavir by about 50%. The garlic was taken in the form of a dietary supplement (GarliPure, Maximum Allicin Formula caplets) twice daily for 20 days. Saquinavir 1.2 g three times daily was given for 4-day periods before, during and after the garlic supplement. Fourteen days after the garlic supplement was stopped the saquinavir pharmacokinetics had still not returned to baseline values. Of the 9 subjects, 6 had a substantial drop in the AUC of saquinavir while taking garlic, then a rise when garlic was stopped. The remaining 3 had no change in the AUC of saquinavir while taking garlic, but had a drop when garlic was stopped. However, in another study, garlic extract (Garlipure) 1.2 g daily for 3 weeks had no significant effect on the pharmacokinetics of a single 1.2-g dose of saquinavir (a slight decrease in AUC in 7 subjects and a slight increase in 3).

In a study in 10 healthy subjects the use of a garlic extract (10 mg, equivalent to 1 g of fresh garlic) twice daily for 4 days did not significantly affect the pharmacokinetics of a single 400-mg dose of ritonavir. There was a non-significant 17% decrease in the AUC of ritonavir. The garlic was given in the form of capsules (Natural Source Odourless Garlic Life Brand). Gastrointestinal toxicity was noted in 2 patients taking garlic or garlic supplements when they started to take ritonavir-containing regimens.

Experimental evidence

In an experimental study using cell lines, allicin, a major active constituent of garlic, significantly decreased the clearance (efflux) of ritonavir from the cells in a dose-dependent manner.

Mechanism

The mechanism of this interaction is uncertain, but it is thought that garlic reduced the bioavailability of saquinavir by increasing its metabolism in the intestine. Why there was a disparity in the effect of garlic on saquinavir between patients is unclear.

Allicin is thought to have inhibited the activity of P-glycoprotein in vitro, which caused the build-up of ritonavir within the cell.

Importance and management

Although information is limited, a reduction in saquinavir plasma levels of the magnitude seen in the first study could diminish its antiviral efficacy. All garlic supplements should probably be avoided in those taking saquinavir as the sole protease inhibitor, but note that this is no longer generally recommended. The effect of garlic on saquinavir levels in the presence of ritonavir (as a pharmacokinetic enhancer) does not appear to have been studied. The pharmacokinetic effect on single-dose ritonavir was not clinically important, but this requires confirmation in a multiple-dose study

Garlic + Rifampicin (Rifampin)

The information regarding the use of garlic with rifampicin is based on experimental evidence only.

Clinical evidence

No interactions found.

Experimental evidence

In a study in rabbits, a garlic extract, produced from blended garlic cloves (exact dosage unknown) and given orally over 14 days, did not alter the AUC and maximum serum levels of a single 24-mg/kg dose of rifampicin, when compared with the levels attained after a single 24-mg/kg dose of rifampicin given 7 days before the garlic extract.

Mechanism

No mechanism expected.

Importance and management

Evidence appears to be limited to this one study in animals. Nevertheless, what is known suggests that no changes in the dose of rifampicin are likely to be needed if it is also taken with garlic.

Garlic + Warfarin and related drugs

An isolated report described increases in the anticoagulant effects of warfarin in two patients taking garlic supplements. Another report described a decrease in anticoagulant effects of fluindione in a patient taking garlic tablets. Garlic supplements alone have also rarely been associated with bleeding. However, in one study, aged garlic extract did not increase the INR or risk of bleeding in patients taking warfarin.

Clinical evidence

(a) Fluindione

In an 82-year-old man stabilised on fluindione 5mg (dosage frequency not stated) for chronic atrial fibrillation, the INR dropped to below its usual range (2 to 3) when garlic tablets 600 mg daily were taken, and remained below 2 for 12 consecutive days despite an increase in fluindione dosage to 10 mg. The INR returned to normal, with an associated reduction in fluindione dose, when the garlic tablets were stopped. He was also taking enalapril 20 mg, furosemide 40 mg and pravastatin 20 mg (dosage frequency not stated).

(b) Warfarin

The INR of a patient stabilised on warfarin more than doubled and haematuria occurred 8 weeks after the patient started to take three Hofels garlic pearles daily. The situation resolved when the garlic was stopped. The INR rose on a later occasion while the patient was taking two Kwai garlic tablets daily. The INR of another patient was also more than doubled by six Kwai garlic tablets daily.

In contrast, in a placebo-controlled study in 48 patients stabilised on warfarin, there was no change in INR or evidence of increased bleeding in those receiving 5mL of aged garlic extract (Kyolic) twice daily for 12 weeks. Similarly, in a preliminary report of the use of alternative and complementary medicines in 156 patients taking warfarin, there was no apparent increased risk or bleeding or raised INRs in 57 patients taking potentially interacting complementary medicines (garlic in 10%), compared with 84 who did not.

Experimental evidence

No relevant data found.

Mechanism

Garlic has been associated with decreased platelet aggregation. See antiplatelet drugs for possible mechanisms. This effect on platelet aggregation has, on at least two documented occasions, led to spontaneous bleeding in the absence of an anticoagulant. These effects might therefore increase the risk of bleeding with anticoagulants. However, this would not cause an increase in INR, and the mechanism for this effect in the cases seen is unknown.

Importance and management

Information about an adverse interaction between coumarin anticoagulants and garlic seems to be limited to these two reports, with warfarin and fluindione. Bearing in mind the wide-spread use of garlic and garlic products, the limited information from the reviewand the study with aged garlic extract, it seems most unlikely that garlic usually has any generally important interaction with anticoagulants. Nevertheless, bear the possibility in mind in the event of an unexpected response to treatment.

In addition, garlic may have some antiplatelet effects and, although there appear to be no clinical reports of an adverse interaction between garlic and antiplatelet drugs, it may be prudent to consider the potential for an increase in the severity of bleeding if garlic is given with anticoagulants. See Garlic + Antiplatelet drugs.