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Overview: Garlic is used for many different reasons, but its benefits are not well defined. It is available as a dietary supplement that can be swallowed and an essential oil that may be applied to the skin. Common side effects include breath or body odor, gas, nausea, or stomach pain. When fresh garlic or pure garlic essential oil is applied to the skin, it can cause irritation and burns. Before using garlic, make sure to tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is garlic used for?

Garlic (Allium sativum) is used for various reasons. However, its benefits are not well defined. Some common reasons that people use garlic include the following.

Garlic may also be used for other conditions as determined by your health care provider.

Note: The Food and Drug Administration (FDA) has not reviewed garlic for safety and effectiveness, and it is not approved by the FDA. Learn more about dietary supplements here. Learn more about essential oils here.

How does garlic work (mechanism of action)?

Garlic is a plant called Allium sativum. The bulb (clove) of the plant is commonly added to foods, and it is also available as a dietary supplement. Garlic can also be added to oils or made into an essential oil. 

Garlic naturally contains many different sulfur-based chemicals, including alliin. When garlic is crushed, chewed, or chopped, alliin is turned into allicin, which has various effects in the body. It can lower the amount of cholesterol made by the liver and increase the breakdown of bad (LDL) cholesterol. It can also increase the amount of insulin made by your pancreas, which can help lower blood sugar levels. Allicin may also make the platelets in your blood less sticky, which can help with blood flow through your blood vessels.

Some research shows that taking garlic can lower the levels of cholesterol and sugar in the blood by a small amount. It may also lower blood pressure by a small amount. But garlic comes in many different forms and doses, and the benefits of most forms of garlic are not well defined.

Allicin can act as an antioxidant and may kill the microbes that cause infections, such as bacteria and fungi. Some people take garlic to help reduce the risk of cancer and boost the immune system. But the benefits of garlic for these uses are not well defined. Garlic is also sometimes applied to the skin to treat skin and nail infections, but its benefits are unclear. 

Some garlic oils are essential oils, which contain chemicals different from other forms of garlic. For example, garlic essential oil does not contain allicin. Instead, it contains chemicals that come from allicin, which have slightly different effects in the body. Garlic essential oil is made by heating up the garlic bulb until certain chemicals, called volatile aromatic compounds, are released. These volatile aromatic compounds, which smell like garlic, are made into garlic essential oil. 

Herbal products, such as garlic, naturally contain many different chemicals. The amounts of each chemical in a specific garlic product may vary. Some, none, or all of these chemicals may have effects on the body. These effects may change depending on how much of each chemical is found in the product you are using.

How should I store garlic?

You should store garlic according to the product label. Most dietary supplements should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight.

Side Effects

What are the most common side effects of garlic?

The most common side effects of garlic are listed below. These side effects may vary depending on how you use garlic, the dose you are taking, or the specific product you are using. Tell your health care provider if you have any of these side effects that bother you.

  • Breath or body odor
  • Gas
  • Nausea
  • Stomach pain
  • Irritation and burns (when applied to the skin)

There may be other side effects of garlic that are not listed here. Contact your health care provider if you think you are having a side effect of a supplement. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of garlic?

While less common, the most serious side effects of garlic are described below, along with what to do if they happen.

Severe Allergic Reactions. Garlic may cause allergic reactions, which can be serious. Stop using garlic and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching or skin rash
  • Bumps on the skin called hives, which can be red, pink, white, or brown depending on your skin tone
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Skin Reactions. Applying fresh, raw garlic or garlic oil to your skin can cause skin reactions, such as rashes, blisters, and burns. In some people, these skin reactions may be caused by an allergy to garlic (contact dermatitis). Stop applying garlic to your skin and contact your health care provider right away if you have a skin reaction.

Warnings & Precautions

Who should not use garlic?

Allergies to Ingredients. People who are allergic to any of the following should not use garlic.

  • Allium sativum
  • Da-suan
  • Garlic
  • Any of the ingredients in the specific product

Your pharmacist can tell you all of the ingredients in the specific garlic products they stock.

What should I know about garlic before using it?

Garlic is available as a dietary supplement and in products that are applied to the skin. It cannot be marketed to treat or cure a disease.

Read and follow the directions on the specific product you are using, or use it as recommended by your health care provider.

Keep garlic out of the reach of children.

Herbal products, such as garlic, naturally contain many different chemicals. The amount of each chemical in a specific garlic product can change for many reasons, including the area where the plant was grown, the weather during growth, the time of year when it was harvested, and the way the plant was processed after it was harvested. If you switch to a new bottle or a different brand, you may not have the same effects or side effects because of this variability. Talk to your health care provider if you have questions or concerns.

Garlic is available in many different forms. The most common form of garlic is a dried powder that is added to food or made into tablets or capsules. There are also aged garlic extracts, which are soaked in alcohol for 20 months and then made into a liquid or powder. Garlic is also available as an infused oil, which means that the oil has absorbed some of the chemicals and flavor of garlic over time. This is different from garlic essential oil, which is made by heating garlic to draw out certain chemicals, called volatile aromatic compounds. Each of these forms of garlic contain different amounts of the chemicals that are naturally found in the plant, changing its effects on the body. If you switch between different types of garlic products or different brands, you may not have the same effects or side effects. Talk to your health care provider if you have questions or concerns.

Certain forms of garlic may be very irritating to the skin and can even cause serious burns. Fresh, raw garlic should not be applied directly to your skin because it contains chemicals that can burn the skin. You should also not apply 100% pure garlic essential oil to your skin. Instead, it should be mixed with other products, such as another oil, cream, or lotion. Follow the instructions on the product label.

The FDA has not tested garlic products to confirm whether they contain the ingredients stated on their labels. Some dietary supplements have been tested by third-party organizations to confirm that they contain the ingredients listed on their labels and do not contain any harmful chemicals. Learn more about how to choose a safe dietary supplement product here. There are no third-party organizations that test essential oils to confirm if they contain the ingredients listed on their labels and do not contain any harmful chemicals.

What should I tell my health care provider before using garlic?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if garlic is right for you.

In particular, make sure that you discuss any of the following.

Allergies to Certain Plants. Garlic is closely related to other plants, such as onions, leeks, and chives. People who have an allergy to these other plants may be more likely to have an allergic reaction to garlic. If you have an allergy to one of these plants, talk to your health care provider before using garlic.

Other Current and Past Health Conditions. Tell your health care provider if you have any of the following.

  • Bleeding problems
  • Upcoming surgery or other medical procedure

Other Medicines and Supplements. Garlic may interact with other medicines and supplements. Before using garlic, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how garlic could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. Garlic passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does garlic interact with foods or drinks?

There are no known interactions between garlic and foods or drinks.

It is unknown if drinking alcohol will affect garlic.

Does garlic interact with medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before using garlic.

  • A blood thinner, which is a medicine used to treat or prevent blood clots
  • An antiplatelet medicine, such as aspirin/dipyridamole, cilostazol, clopidogrel (Plavix), or ticagrelor (Brilinta), which is a medicine used to prevent blood clots
  • Aspirin, which is in many prescription and OTC products, including those for pain, swelling, and fever
  • A medicine for diabetes
  • A protease inhibitor, such as atazanavir (Reyataz), nelfinavir (Viracept), or ritonavir (Norvir), which is a medicine commonly used to treat HIV

Garlic may alter the blood levels of some medicines. Tell your health care provider about all medicines that you take or have recently taken.

The interactions between garlic and medicines are not fully understood. As with most dietary supplements, the research on drug interactions with garlic is incomplete. Always check with your health care provider before using garlic with any medicines.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much garlic?

If you or someone else has used too much garlic, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

Garlic is available in many different doses and forms that can each have different effects on the body. Read the product label closely and speak with a health care provider about how to use garlic safely. Do not use double or extra doses, even if you miss a dose.