Anticoagulant, so may enhance effect of blood thinners. Mouth ulcers, inflamed mouth tissues from chewing leaf. GI discomfort and dry mouth. Possible nausea, heartburn, dizziness. Topical garlic can cause skin irritation, blistering and burns.
Fresh garlic is the best form.
Garlic contains allin and allicin. People with gallstones should not take ginger without consulting a doctor. Side effects rare. Menstrual abnormalities, breast tenderness. Do not take with stimulants, including excessive caffeine.