Concentrated garlic supplements can increase bleeding risk with anticoagulants or antiplatelet medicine. Garlic can also reduce exposure to some HIV and transplant medicines, add to insulin's glucose-lowering effect, and alter CYP or P-glycoprotein drug handling.

Use with caution. Healthcare professional review recommended before use.

Contraindications

Active bleeding tendency
Perioperative use of concentrated garlic supplements
Marked Stomach heat or mucosal irritation aggravated by pungent foods

Cautions

MSK notes that garlic can alter platelet function and should be stopped at least 7 days before surgery when used as a supplement.
Food-level garlic and concentrated garlic extracts are not interchangeable from an interaction or bleeding-risk standpoint.
Topical garlic can cause chemical burns and should not be treated like a harmless household skin treatment.

Drug Interactions

Drug Class / Substrate	Mechanism	Severity	Source
Warfarin, anticoagulants, and antiplatelet medicines	Garlic can reduce platelet aggregation and increase bleeding or bruising risk.	Major	Memorial Sloan Kettering About Herbs
Darunavir, saquinavir, and other protease inhibitors	Garlic use has reduced antiretroviral concentrations, with treatment failure reported in cases involving darunavir.	Major	Memorial Sloan Kettering About Herbs
Cyclosporine	Garlic may reduce cyclosporine effectiveness and create a transplant-rejection risk.	Major	Memorial Sloan Kettering About Herbs
Insulin and other glucose-lowering medicines	Garlic supplements may add to glucose-lowering effects and require closer monitoring.	Moderate	Memorial Sloan Kettering About Herbs
CYP2C9, CYP2C19, CYP3A4, and P-glycoprotein substrate medicines	Garlic products can alter drug metabolism or transport, although effects vary by preparation and evidence is mixed for CYP3A4.	Uncertain	Memorial Sloan Kettering About Herbs

This information is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before using herbal medicines, especially if you take prescription medications.