Based on NIH | Is it true that taking garlic or garlic supplements with omeprazole increases the risk of side effects or adverse interactions?

Quick answer

Garlic (including supplements like aged garlic extract or allicin) can interact with omeprazole by affecting how your body breaks it down, which may raise omeprazole levels in some people and potentially increase side effects. ^[1] It can also add a blood‑thinning effect on platelets, so if you use other drugs that affect bleeding, caution is advised, although this is not specific to omeprazole. ^{[2] [3]}

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How garlic may interact with omeprazole

• CYP2C19 inhibition: Omeprazole is mainly metabolized by the enzyme CYP2C19. Allicin (a key compound from garlic) has been shown in healthy volunteers to inhibit CYP2C19, leading to higher omeprazole blood levels in people with certain common genotypes. ^[1] In that study, after 14 days of allicin, peak omeprazole concentration increased by roughly 50% and total exposure (AUC) by about 48–74% in participants with typical CYP2C19 function, while a marker of CYP2C19 activity decreased. ^[1] There was no meaningful effect in individuals with poor‑metabolizer genotypes, and CYP3A4 activity was not significantly changed. ^[1]

• What this could mean clinically: When omeprazole levels rise, you could be more likely to experience dose‑related effects such as headache, abdominal discomfort, constipation or diarrhea, or, rarely, dizziness, though individual responses vary. ^[1] Product information for omeprazole advises discussing use of herbal supplements with your clinician because omeprazole can affect other medicines and can be affected by them. ^{[4] [5]}

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Bleeding considerations with garlic

• Antiplatelet properties: Garlic supplements can reduce platelet aggregation (platelets help blood to clot), which may increase bruising or bleeding risk, especially if combined with blood thinners like warfarin or antiplatelet agents. ^[3] Guidance commonly recommends stopping garlic supplements 1–2 weeks before surgery due to potential bleeding risk. ^[3] Mechanistically, garlic products may inhibit CYP2C19 in vitro and influence drug transporters, which is another reason to use caution with drug combinations. ^[6]

• Not specific to omeprazole: Omeprazole itself is not a blood thinner; the bleeding caution with garlic mainly matters if you also take anticoagulants or antiplatelet drugs, or you have upcoming surgery. ^[3] A small clinical study in diabetes found aged garlic extract did not further enhance the antiplatelet effect of cilostazol compared with either alone over 7 days, but larger trials are needed, and results may not generalize to other drugs. ^[7]

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Practical guidance

• If you use garlic supplements: Consider that allicin may raise omeprazole levels depending on your CYP2C19 genetics; if you notice more gastrointestinal or neurologic side effects after adding garlic, discuss dose timing or adjustments with your clinician. ^[1] Since official labeling advises you to tell your doctor about vitamins and herbal products, it is reasonable to report garlic use. ^{[4] [5]}

• If you take blood thinners or have surgery planned: Avoid starting garlic supplements without medical advice and stop them in advance of surgery as recommended, because of potential bleeding risk. ^[3]

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Key points to remember

• Garlic/allicin can inhibit CYP2C19 and increase omeprazole exposure in many people, which could increase side effects. ^[1]
• Garlic supplements have antiplatelet effects; use caution if you’re on anticoagulants/antiplatelets or facing surgery. ^[3]
• Omeprazole labeling advises discussing herb and supplement use because interactions are possible. ^{[4] [5]}

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Summary table

Topic	What happens	Who is affected	Clinical note
Allicin effect on omeprazole	Inhibits CYP2C19 → higher omeprazole levels (↑Cmax and ↑AUC)	People with common CYP2C19 genotypes (normal/intermediate metabolizers)	May increase omeprazole side effects; monitor symptoms
CYP3A4 effect	No significant change	All genotypes in study	Less concern via CYP3A4 pathway
Platelet effects of garlic	Reduced platelet aggregation → potential bleeding	Anyone, especially on blood thinners or pre‑surgery	Stop 1–2 weeks before surgery; caution with anticoagulants/antiplatelets
Labeling advice	Report vitamins/herbals	All omeprazole users	Helps clinicians manage interactions

^{[1] [3] [4] [5] [7] [6]}