Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.

The effectiveness ratings for GARLIC are as follows:

• Hardening of the arteries (atherosclerosis). As people age, their arteries tend to lose their ability to stretch and flex. Garlic seems to reduce this effect.

• Colon cancer, rectal cancer. Research suggests that eating garlic can reduce the risk of developing colon or rectal cancer. Research suggests that taking high doses of aged garlic extract daily for 12 months reduces the risk of developing new tumors. However, other garlic supplements do not seem to offer the same benefit.

• Stomach cancer. Some evidence suggests that eating more garlic can decrease the risk of developing stomach cancer. However, taking a specific aged garlic extract (Kyolic, Wakunaga Pharmaceutical Co.) for about 7 years does not seem to reduce the risk.

• High blood pressure. Some research shows that garlic can reduce blood pressure in people with high blood pressure by as much as 7% or 8%. It also seems to lower blood pressure in people with normal blood pressure. Most studies have used a specific garlic powder product (Kwai, from Lichtwer Pharma).

• Tick bites. People who consume high amounts of garlic over about a 5-month period seem to have a reduced the number of tick bites.

• Ringworm. Applying a gel containing 0.6% ajoene, a chemical in garlic, seems to be as effective as antifungal medication for treating ringworm.

• Jock itch. Applying a gel containing 0.6% ajoene, a chemical in garlic, seems to be as effective as antifungal medication for treating jock itch.

• Athlete’s foot. Applying a gel containing 1% ajoene, a chemical in garlic, seems to be effective for treating athlete’s foot. A garlic gel with 1% ajoene seems to be about as effective for athlete’s foot as the medicine Lamisil.

• Breast cancer. Taking garlic does not seem to reduce the risk of developing breast cancer.

• Cystic fibrosis. Research suggests that taking garlic oil macerate daily for 8 weeks does not improve lung function, symptoms, or the need for antibiotics in children with cystic fibrosis and lung infection.

• Diabetes. Some research suggests that taking a specific garlic product (Allicor) along with antidiabetes medication for 4-24 weeks can reduce blood sugar, cholesterol, and triglycerides in people with diabetes. However, analyses of research suggest that garlic does not seem to have any effect on blood sugar or cholesterol in people with or without diabetes.

• Inherited high cholesterol. In children with high levels of low-density lipoprotein (LDL or “bad”) cholesterol, taking garlic powdered extract by mouth does not seem to improve cholesterol levels or blood pressure.

• Infections caused by helicobacter pylori (H. pylori) bacteria. Taking garlic by mouth for H. pylori infection used to look promising due to laboratory evidence showing potential activity against H. pylori. However, when garlic cloves, powder, or oil is used in humans, it does not seem to help treat people infected with H. pylori.

• High cholesterol. Research on the effects of garlic on cholesterol and triglyceride levels is inconsistent. However, if only the high quality studies are considered, reviewers conclude that garlic does not significantly lower cholesterol or triglyceride levels.

• Lung cancer. Taking garlic by mouth does not seem to reduce the risk of developing lung cancer.

• Mosquito repellent. Taking garlic by mouth does not seem to repel mosquitos.

• Leg pain caused by poor blood circulation in the legs (peripheral arterial disease or PAD). Taking garlic for 12 weeks does not seem to reduce leg pain when walking due to poor circulation in the legs.

• High blood pressure in pregnancy (pre-eclampsia). Some early evidence suggests that taking a specific garlic extract (Garlet) daily during the third trimester of pregnancy does not reduce the risk of developing high blood pressure in women who are at high risk or pregnant for the first time.

• Hair loss (alopecia areata). Early evidence suggests that applying a garlic 5% gel, along with a topical steroid, for 3 months increases hair growth in people with hair loss.

• Chest pain (angina). Early research suggests that administering garlic intravenously (by IV) for 10 days reduces chest pain compared to intravenous nitroglycerin.

• Benign prostatic hyperplasia (BPH). There is some early evidence that taking garlic by mouth might be helpful for improving urinary flow, decreasing urinary frequency, and other symptoms associated with BPH.

• Common cold. Early research suggests garlic might reduce the frequency and number of colds when taken for prevention.

• Clogged arteries (coronary heart disease). Early research suggests that taking a specific garlic product (Allicor) for 12 months reduces the risk of sudden death and heart attack in people at risk for developing clogged arteries. Other early research suggests that taking a supplement containing aged garlic might prevent additional clogging of the arteries.

• Corns. Early studies suggest that applying certain garlic extracts to corns on the feet twice daily improves corns. One particular garlic extract that dissolves in fat has an effect after 10-20 days of treatment, but a water soluble extract can take up to two months to show improvement.

• Cancer in the esophagus. Early research on the use of garlic for preventing cancer in the esophagus is inconsistent. Some evidence suggests that eating raw garlic does not prevent the development of cancer in the esophagus. However, other research suggests that consuming garlic weekly does decrease the risk of developing cancer in the esophagus

• Muscle soreness after exercise. Early evidence suggests that takinga allicin, a chemical in garlic, daily for 14 days can reduce muscle soreness after exercise in athletes.

• Exercise performance. Early evidence suggests that taking a single 900 mg dose of garlic before exercise can increase endurance in young athletes.

• Lumpy breast tissue (fibrocystic breast disease). Early research suggests that taking a specific combination product (Karinat) containing garlic, beta-carotene, vitamin E, and vitamin C twice daily for 6 months reduces the severity of breast pain, premenstrual syndrome, and lumpy breast tissue in people with fibrocystic breast disease.

• Stomach inflammation (gastritis). Early research suggests that taking a specific combination product containing garlic (Karinat) twice daily for 6 months improves digestion, stops the growth of certain bacteria (H. pylori), and reduces the risk of stomach cancer in people with stomach inflammation. However, the effects of garlic alone has not been determined.

• Hepatitis. Early research suggests that taking garlic oil together with diphenyl-dimethyl-dicarboxyale improves liver function in people with hepatitis. However, the effects of garlic alone are not clear.

• Shortness of breath and low oxygen levels associated with liver disease (hepatopulmonary syndrome). Early research suggests that garlic oil might improve oxygen levels in people with hepatopulmonary syndrome.

• Lead poisoning. Research suggests that taking garlic three times daily for 4 weeks can reduce blood lead concentrations in people with lead poisoning. However, it does not seem to be more effective than D-penicillamine.

• Cancer of certain bone marrow cells (multiple myeloma). Early evidence suggests that taking garlic might decrease the risk of developing cancer of the plasma cells in the bone marrow.

• Thrush (oral candidiasis). Early research suggests that applying garlic paste to affected areas in the mouth can increase the healing rate in people with oral thrush. Other early research suggests that using a garlic mouthwash three times daily for 4 weeks improves redness.

• Prostate cancer. Men in China who eat about a clove of garlic daily seem to have a 50% lower risk of developing prostate cancer. However, research in Iranian men suggests that eating garlic has no effect on prostate cancer risk. Whether this research applies to men in Western countries is not known. Some early research suggests that taking garlic supplements might reduce the risk of developing prostate cancer or reduce symptoms associated with prostate cancer.

• Hardening and tightening of the skin and connective tissue (scleroderma). Research suggests that taking garlic daily for 7 days does not benefit people with scleroderma.

• Warts. Early evidence suggests that applying a specific fat soluble garlic extract to warts on the hands twice daily removes warts within 1-2 weeks. Also, a water-soluble garlic extract seems to provide modest improvement, but only after 30-40 days of treatment.

• For high blood pressure:

• Garlic extract 600-1200 mg divided and given three times daily.

• Standardized garlic powder extract containing 1.3% alliin content has been studied for this use.

• Aged garlic extract 600 mg to 7.2 grams per day has also been used. Aged garlic typically contains only 0.03% alliin.

• Fresh garlic 4 grams (approximately one clove) once daily has also been used. Fresh garlic typically contains 1% alliin.

• For prevention of colon, rectal, and stomach cancer: fresh or cooked garlic 3.5-29 grams weekly.

• For fungal skin infections (ringworm, jock itch, athlete’s foot): garlic ingredient ajoene as a 0.4% cream, 0.6% gel, and 1% gel applied twice daily for one week.

To learn more about how this article was written, please see the Natural Medicines Comprehensive Database methodology.

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