Common Side Effects of Garlic
Garlic is generally safe in food amounts but can cause mild issues when taken as supplements or in larger doses. These include bad breath, body odor, heartburn, gas, nausea, vomiting, and diarrhea. Skin irritation or rash may occur from topical use.[1][2]
Serious Risks and Allergic Reactions
High doses increase bleeding risk due to anti-clotting effects, which can lead to bruising, nosebleeds, or surgical complications—stop garlic supplements at least two weeks before surgery. Rare severe reactions include allergic responses like hives, swelling, or anaphylaxis.[1][3]
Interactions with Medications
Garlic slows blood clotting, so it heightens bleeding risks with anticoagulants like warfarin, aspirin, or antiplatelet drugs. It may lower blood pressure too much when combined with hypertension meds and reduce effectiveness of HIV protease inhibitors or saquinavir.[2][4]
Who Should Avoid Garlic Supplements
Pregnant or breastfeeding women should stick to food amounts due to insufficient safety data on high doses. People with stomach ulcers, low blood pressure, or bleeding disorders face higher risks. Children under 12 may experience stomach upset.[1][3]
How Much Garlic Triggers Side Effects
Culinary use (1-2 cloves daily) rarely causes problems. Supplements over 1,200 mg/day of alliin (active compound) or aged garlic extract above 2,400 mg/day more often lead to digestive upset or bleeding risks.[2]
[1] National Institutes of Health (NIH) Office of Dietary Supplements - Garlic Fact Sheet
[2] Mayo Clinic - Garlic
[3] WebMD - Garlic
[4] Mount Sinai Health Library - Garlic