Garlic has been used as both food and medicine for thousands of years, dating back to when the Egyptian pyramids were built. In early 18th century France, gravediggers drank crushed garlic in wine believing it would protect them from the plague. During both World War I and II, soldiers were given garlic to prevent gangrene. It was also used as an antiseptic and applied to wounds to prevent infection.

Today garlic is used to help prevent heart disease, including atherosclerosis or hardening of the arteries (plaque buildup in the arteries that can block the flow of blood and may lead to heart attack or stroke), high cholesterol, high blood pressure, and to boost the immune system. Eating garlic regularly may also help protect against cancer.

Garlic is rich in antioxidants. In your body, harmful particles called free radicals build up as you age and may contribute to heart disease, cancer, and Alzheimer disease. Antioxidants like those found in garlic fight off free radicals, and may reduce or even help prevent some of the damage they cause over time.

The conditions for which garlic is showing the most promise include the following:

Heart disease

Garlic is most often mentioned as an herb for heart disease and atherosclerosis (hardening of the arteries). But evidence is mixed. Some studies suggest that garlic may help prevent heart disease. It may slow down atherosclerosis and lower blood pressure a little, between 5% and 8%. Most of the studies on high blood pressure use a specific formulation called Kwai. One study that lasted 4 years found that people who took 900 mg daily of standardized garlic powder slowed the development of atherosclerosis. Garlic also seems to act as a blood thinner, which may help prevent heart attacks and strokes.

Earlier studies found that garlic lowered high cholesterol. But almost all recent studies that are high quality have found that garlic didn't lower cholesterol.

Common cold

Early evidence suggests garlic may help prevent colds. In one study, people took either garlic supplements or placebo for 12 weeks during cold season, between November and February. Those who took garlic had fewer colds than those who took placebo. And when they did get a cold, the people taking garlic saw their symptoms go away faster than those who took placebo.

Cancer

Garlic may strengthen the immune system, helping the body fight diseases such as cancer. In test tubes, garlic seems to kill cancer cells. And population studies, ones that follow groups of people over time, suggest that people who eat more raw or cooked garlic are less likely to get colon and stomach cancers and cancer of the esophagus. In fact, researchers who reviewed 7 studies found a 30% reduction in risk of colorectal cancer among people who ate a lot of raw or cooked garlic. Garlic supplements do not seem to have the same effect.

• A large-scale study, called the Iowa Women's Health Study, looked at how much garlic, fruit, and vegetables were in the diets of 41,000 middle-aged women. Results showed that women who regularly ate garlic, fruits, and vegetables had a 35% lower risk of developing colon cancer.
• Garlic may help the immune system function better during times of need such as in cancer. In a study of 50 people with inoperable colorectal, liver, or pancreatic cancer, immune activity improved after they took aged garlic extract for 6 months.

Other uses

• In test tubes, garlic killed roundworms, Ascaris lumbricoides, the most common type of intestinal parasite. But it has not been tested in humans, so researchers do not know if it works in people.
• One study found that men with benign prostatic hyperplasia (enlarged prostate) had fewer urinary symptoms when they took garlic, compared to men who took placebo. The garlic also reduced prostate size. More research is needed to see if garlic really helps men with enlarged prostate.
• Several studies report that a garlic gel applied to the skin may treat ringworm, jock itch, and athlete's foot.

Garlic is a perennial that originally came from central Asia, and is now grown throughout the world. It can grow 2 feet high or more. The compound bulb is the part used for medicine. Each bulb is made up of 4 to 20 cloves, and each clove weighs about 1 gram. Garlic supplements can either be made from fresh, dried, aged, or garlic oil. Each may have different effects on the body.

Researchers once thought that a chemical called allicin was responsible for garlic's benefits, as well as its distinctive smell. But there are other chemicals in garlic, including some sulfur-containing compounds, that may help fight heart disease and prevent some cancers.

Garlic supplements are made from whole fresh garlic, dried, or freeze-dried garlic, garlic oil, and aged garlic extracts.

Not all garlic contains the same amount of active ingredients. It is important to read the label carefully. To get the most benefit, use standardized garlic products. Also, follow the directions of a health care provider who is experienced in herbal medicine.

Pediatric

Ask your doctor before giving garlic supplements to a child. Research has not yet found what an effective and safe dose might be for children.

Adult

Ask your doctor for dosing instructions.

The use of herbs is a time-honored approach to strengthening the body and treating disease. However, herbs can trigger side effects, and interact with other herbs, supplements, or medications. For these reasons, you should take herbs under the supervision of a health care provider qualified in the field of botanical medicine.

Garlic is listed as Generally Recognized as Safe (GRAS) by the U.S. Food and Drug Administration (FDA).

Side effects include upset stomach, bloating, bad breath, body odor, and a stinging sensation on the skin from handling too much fresh or dried garlic. Handling garlic may also cause skin lesions. Other, more rare side effects that have been reported by those taking garlic supplements include headache, fatigue, loss of appetite, muscle aches, dizziness described as vertigo, and allergies such as an asthmatic reaction or skin rash.

Garlic acts like a blood thinner. Too much garlic can increase your risk for bleeding during or after surgery. It may also interact with blood-thinning medications.

People with ulcers or thyroid problems should ask their doctors before taking garlic.

Garlic may interact with a number of medications. Some of these medications are listed below. To be safe, if you take any prescription medicines, ask your doctor before taking garlic supplements.

Isoniazid (Nydrazid): This medication is used to treat tuberculosis. Garlic may interfere with the absorption of isoniazid, meaning the drug might not work as well.

Birth control pills: Garlic may make birth control pills less effective.

Cyclosporine: Garlic may interact with cyclosporine, a medication taken after organ transplant, and make it less effective.

Blood-thinning medications: Garlic may make the actions of blood-thinning medications including warfarin (Coumadin), clopidogrel (Plavix), and aspirin stronger, increasing the risk of bleeding.

Medications for HIV/AIDS: Garlic may lower blood levels of protease inhibitors, medications used to treat people with HIV. Protease inhibitors include:

• Amprenavir (Agenerase)
• Fosamprenavir (Lexiva)
• Indinavir (Crixivan)
• Nelfinavir (Viracept)
• Ritonavir (Norvir)
• Saquinavir (Fortovase)

Nonsteroidal anti-inflammatory drugs (NSAIDs): Both NSAIDs and garlic may increase the risk of bleeding. NSAIDs include ibuprofen (Advil, Motrin) and naproxen (Aleve), as well as prescription medications.

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