Garlic : Interactions

by MedlinePlus

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Pregnancy and Breastfeeding

Garlic is likely safe during pregnancy in amounts usually eaten in food, based on historical use. However, garlic supplements or large amounts of garlic should be avoided during pregnancy due to a possible increased risk of bleeding. In addition, early animal studies suggest that garlic may cause contraction of the uterus. Many tinctures contain high levels of alcohol, and should be avoided during pregnancy.

Garlic is likely safe during breastfeeding in amounts usually eaten in food, based on historical use. However, some mothers who take garlic supplements report increased nursing time, milk odor, and reduced feeding by the infant. The safety of garlic supplements during breastfeeding is not known.

Interactions

Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy.

Interactions with Drugs

Human reports suggest that garlic may increase the risk of bleeding when taken with drugs that also increase the risk of bleeding. Examples include aspirin, anticoagulants ("blood thinners") such as warfarin (Coumadin®) or heparin, anti-platelet drugs such as clopidogrel (Plavix®), and non-steroidal anti-inflammatory drugs such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®). Animal and human studies show that garlic can lower blood pressure. Use caution when combining with other medications that lower blood pressure. Several human studies report lower cholesterol in people taking garlic. These effects may be increased if garlic is taken with medications that lower blood cholesterol like lovastatin (Mevacor®) or other "statins" (HMGCoA reductase inhibitors).

Levels of the drug saquinavir, used in HIV treatment, may be reduced if garlic is taken, and its effectiveness may therefore be reduced. Other antiviral drugs like ritonavir may also be affected.

Based on animal studies, garlic may lower blood sugar levels. Although this is theoretical in humans, caution is advised when using medications that may also lower blood sugar. Patients taking drugs for diabetes by mouth or insulin should be monitored closely by a qualified healthcare provider. Medication adjustments may be necessary. Individuals with thyroid disorders or who take thyroid medications should use caution in taking garlic supplements as they may affect the thyroid.

Garlic may alter levels of certain drugs metabolized by the liver's CYP450 enzyme system. Garlic may alter levels of some anti-cancer drugs: a laboratory study showed that ajoene (a natural garlic compound) enhanced the effect of two chemotherapeutic drugs, cytarabine and fludarabine, while treating leukemia.

Many tinctures contain high levels of alcohol, and may cause nausea or vomiting when taken with metronidazole (Flagyl®) or disulfiram (Antabuse ® ).

Interactions with Herbs and Dietary Supplements

Based on human cases, garlic may increase the risk of bleeding. In theory, this risk may be further increased when garlic is taken with other herbs or supplements that also increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba and two cases with saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases. Examples include: alfalfa, American ginseng, angelica, anise, Arnica montana , asafetida, aspen bark, bilberry, birch, black cohosh, bladderwrack, bogbean, boldo, borage seed oil, bromelain, capsicum, cat's claw, celery, chamomile, chaparral, clove, coleus, cordyceps, danshen, devil's claw, dong quai, EPA (eicosapentaenoic acid, found in deep-sea fish oils), evening primrose, fenugreek, feverfew, fish oil, flaxseed/flax powder (not a concern with flaxseed oil), ginger, grapefruit, grapeseed, green tea, guggul, gymnestra, horse chestnut, horseradish, licorice root, lovage root, male fern, meadowsweet, nordihydroguairetic acid (NDGA), onion, papain, Panax ginseng, parsley, passionflower, poplar, prickly Ash, propolis, quassia, red clover, reishi, Siberian ginseng, sweet clover, rue, sweet birch, sweet clover, turmeric , vitamin E, white willow, wild carrot, wild lettuce, willow, wintergreen, and yucca.

Studies in animals and humans suggest that garlic may have a small effect in lowering blood pressure. Caution should be used if taken with other supplements that can lower blood pressure, including: aconite/monkshood, arnica, baneberry, betel nut, bilberry, black cohosh, bryony, calendula, California poppy, coleus, curcumin, eucalyptol, eucalyptus oil, flax/flaxseed oil, ginger, ginkgo, goldenseal, green hellebore, hawthorn, Indian tobacco, jaborandi, mistletoe, night blooming cereus, oleander, pasque flower, periwinkle, pleurisy root, shepherd's purse, Texas milkweed, turmeric, and wild cherry.

Although animal studies report that garlic may lower blood sugar levels, the effect has not been shown in humans. Nonetheless, caution is advised when using herbs or supplements that may also lower blood sugar. Blood glucose levels may require monitoring, and doses may need adjustment. Possible examples include: Aloe vera , American ginseng, bilberry, bitter melon, burdock,fenugreek, fish oil, gymnema, horse chestnut seed extract (HCSE), maitake mushroom, marshmallow, milk thistle, Panax ginseng, rosemary, Siberian ginseng, stinging nettle, and white horehound.

Human studies have shown that garlic may lower cholesterol a small amount. These effects may be larger than expected if taken with other cholesterol-lowering supplements such as fish oil, EPA (eicosapentaenoic acid, found in deep-sea fish oils), guggul, red yeast, or niacin.

Garlic may interact with herbals and dietary supplements that are metabolized by the liver's CYP450 enzyme system.

Garlic and pycnogenol have been shown to increase human growth hormone secretion in laboratory experiments.

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