Garlic has powerful biological effects, so if you are considering using it, note the following advice.
• Skin problems – do a patch test first by applying garlic to a small inconspicuous area and checking after several hours that it has not caused any irritation. Do not apply again if it has. Garlic oil lacks garlic’s irritating agents (sulfenic acids and allicin) but also lacks the bioactivity of allicin and its derivatives. Be very wary of applying garlic to a child’s skin.
• Rectum/anal problems – do not use garlic locally, as it could irritate or burn.
• Stomach or digestive problems – note that large amounts of garlic can irritate the stomach and intestine.
• Bleeding disorders – note that garlic can encourage bleeding. This effect can be exaggerated by also consuming any other herb or supplement that slows blood-clotting, including fish oil, vitamin E, angelica, cloves, ginger, ginkgo, red clover, turmeric, and willow.
• Pregnancy – note that normal dietary amounts of garlic are likely to be safe for the baby, but it is wise to avoid large amounts and not to apply garlic to your skin. If you are due to give birth within 2 weeks, large intakes of garlic might encourage bleeding during childbirth or associated surgical procedures.
• Breastfeeding – avoid consuming or applying large amounts of garlic, because there are insufficient data to confirm their safety for the
baby. Babies spend longer breastfeeding after their mothers have eaten garlic, probably because they like garlic-scented breast milk.
• Awaiting surgery – avoid garlic for 2 weeks before the scheduled surgery, because it can prolong bleeding.
• Chronic heavy drinking – avoid consuming large amounts of garlic, because this could slow the breakdown of the liver’s P450 2E1 enzyme,
which helps to break down alcohol.
• Taking oral contraception containing estrogen – note that garlic could speed its breakdown and endanger birth control. If you
consume a lot of garlic, consider using additional birth control (such as a condom).
• Taking cyclosporine – note that allicin-containing garlic products can decrease its efficacy.
• Taking medications affected by cytochrome P450 enzymes, such as paracetamol (acetaminophen); calcium-channel blockers for high blood
pressure (such as nicardipine), losartan (for high blood pressure), certain anticancer drugs (such as paclitaxel), certain antifungals (such as ketoconazole), cortisol and other glucocorticoids (for allergy and autoimmune disease), chlorzoxazone (a muscle-relaxant), theophylline (for certain respiratory disorders), fentanyl (a pain-reliever), midazolam (for epilepsy), lidocaine (a local anesthetic and a heart medication), and certain anesthetics(such as halothane) – note that garlic can slow the breakdown of these medications, so increasing their effects. Discuss with your doctor whether to avoid or cut back on the garlic.
• Taking the high-blood-pressure medication with a calcium-channel blocker (such as verapamil) – note that garlic’s mild blood-pressure-lowering effects might increase their action. Take regular blood checkups.
• Taking anti-clotting medication (such as aspirin and warfarin) – note that garlic could further reduce clotting, encouraging bruising and bleeding,
though small amounts of garlic are unlikely to be a problem. If you are on warfarin, be sure to have regular blood tests.
• Taking blood-sugar-lowering medication – note that garlic may further lower blood sugar, though normal amounts of garlic are unlikely to be a
problem.
• Taking the anti-TB drug isoniazid – note that you should avoid garlic because it could reduce the drug’s absorption.
• Taking HIV/AIDS medications called non-nucleoside reverse transcriptase inhibitors (such as nevirapine); also, saquinavir as your only protease inhibitor – discuss with your doctor whether to avoid garlic.
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