GARLIC Overview Information
Garlic is an herb. It is best known as a flavoring for food. But over the years, garlic has been used as a medicine to prevent or treat a wide range of diseases and conditions. The fresh clove or supplements made from the clove are used for medicine.
Garlic is used for many conditions related to the heart and blood system. These conditions include high blood pressure, high cholesterol, coronary heart disease, heart attack, and “hardening of the arteries” (atherosclerosis). Some of these uses are supported by science. Garlic actually may be effective in slowing the development of atherosclerosis and seems to be able to modestly reduce blood pressure.
Some people use garlic to prevent colon cancer, rectal cancer, stomach cancer, breast cancer, prostate cancer, and lung cancer. It is also used to treat prostate cancer and bladder cancer.
Garlic has been tried for treating an enlarged prostate (benign prostatic hyperplasia; BPH), diabetes, osteoarthritis, hayfever (allergic rhinitis), traveler's diarrhea, high blood pressure late in pregnancy (pre-eclampsia), cold and flu. It is also used for building the immune system, preventing tick bites, and preventing and treating bacterial and fungal infections.
Other uses include treatment of fever, coughs, headache, stomach ache, sinus congestion, gout, rheumatism, hemorrhoids, asthma, bronchitis, shortness of breath, low blood pressure, low blood sugar, high blood sugar, and snakebites. It is also used for fighting stress and fatigue, and maintaining healthy liver function.
Some people apply garlic oil to their skin to treat fungal infections, warts, and corns. There is some evidence supporting the topical use of garlic for fungal infections like ringworm, jock itch, and athlete’s foot; but the effectiveness of garlic against warts and corns is still uncertain.
There is a lot of variation among garlic products sold for medicinal purposes. The amount of allicin, the active ingredient and the source of garlic’s distinctive odor, depends on the method of preparation. Allicin is unstable, and changes into a different chemical rather quickly. Some manufacturers take advantage of this by aging garlic to make it odorless. Unfortunately, this also reduces the amount of allicin and compromises the effectiveness of the product. Some odorless garlic preparations and products may contain very little, if any, allicin. Methods that involve crushing the fresh clove release more allicin. Some products have a coating (enteric coating) to protect them against attack by stomach acids.
While garlic is a common flavoring in food, some scientists have suggested that it might have a role as a food additive to prevent food poisoning. There is some evidence that fresh garlic, but not aged garlic, can kill certain bacteria such as E. coli, antibiotic-resistant Staphylococcus aureus, and Salmonella enteritidis in the laboratory.
How does it work?
Garlic produces a chemical called allicin. This is what seems to make garlic work for certain conditions. Allicin also makes garlic smell. Some products are made “odorless” by aging the garlic, but this process can also make the garlic less effective. It’s a good idea to look for supplements that are coated (enteric coating) so they will dissolve in the intestine and not in the stomach.
Possibly Effective for:
- 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.
Possibly Ineffective for:
- 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.
GARLIC Side Effects & Safety
Garlic is LIKELY SAFE for most people when taken by mouth. Garlic has been used safely in research for up to 7 years. When taken by mouth, garlic can cause bad breath, a burning sensation in the mouth or stomach, heartburn, gas, nausea, vomiting, body odor, and diarrhea. These side effects are often worse with raw garlic. Garlic may also increase the risk of bleeding. There have been reports of bleeding after surgery in people who have taken garlic. Asthma has been reported in people working with garlic, and other allergic reactions are possible.
Garlic is POSSIBLY SAFE when applied to the skin. Gels, pastes and mouthwashes containing garlic have been used for up to 3 months. However, when applied to the skin, garlic might cause damage to the skin that is similar to a burn.
Special Precautions & Warnings:Pregnancy and breast-feeding: Garlic is LIKELY SAFE to use during pregnancy when taken in the amounts normally found in food. Garlic is POSSIBLY UNSAFE when used in medicinal amounts during pregnancy and when breast-feeding. There is not enough reliable information about the safety of using garlic on the skin if you are pregnant or breast-feeding. Stay on the safe side, and avoid use.
Children: Garlic is POSSIBLY SAFE when taken by mouth and appropriately for a short-term in children. However, garlic is POSSIBLY UNSAFE when taken by mouth in large doses. Some sources suggest that high doses of garlic could be dangerous or even fatal to children; however, the reason for this warning is not known. There are no case reports available of significant adverse events or mortality in children associated with taking garlic by mouth. When applied to the skin, garlic might cause damage to the skin that is similar to a burn.
Bleeding disorder: Garlic, especially fresh garlic, might increase bleeding.
Stomach or digestion problems: Garlic can irritate the gastrointestinal (GI) tract. Use with caution if you have stomach or digestion problems.
Low blood pressure: Garlic can lower blood pressure. In theory, taking garlic might make blood pressure become too low in people with low blood pressure.
Surgery: Garlic might prolong bleeding. Stop taking garlic at least two weeks before a scheduled surgery.
Major Interaction Do not take this combination
- Isoniazid (Nydrazid, INH) interacts with GARLIC
Garlic might reduce how much isoniazid (Nydrazid, INH) the body absorbs. This might decrease how well isoniazid (Nydrazid, INH) works. Don't take garlic if you take isoniazid (Nydrazid, INH).
- Medications used for HIV/AIDS (Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs)) interacts with GARLIC
The body breaks down medications used for HIV/AIDS to get rid of them. Garlic can increase how fast the body breaks down some medication for HIV/AIDS. Taking garlic along with some medications used for HIV/AIDS might decrease the effectiveness of some medications used for HIV/AIDS.
Some of these medications used for HIV/AIDS include nevirapine (Viramune), delavirdine (Rescriptor), and efavirenz (Sustiva).
- Saquinavir (Fortovase, Invirase) interacts with GARLIC
The body breaks down saquinavir (Fortovase, Invirase) to get rid of it. Garlic might increase how quickly the body breaks down saquinavir. Taking garlic along with saquinavir (Fortovase, Invirase) might decrease the effectiveness of saquinavir (Fortovase, Invirase).
Moderate Interaction Be cautious with this combination
- Birth control pills (Contraceptive drugs) interacts with GARLIC
Some birth control pills contain estrogen. The body breaks down the estrogen in birth control pills to get rid of it. Garlic might increase the breakdown of estrogen. Taking garlic along with birth control pills might decrease the effectiveness of birth control pills. If you take birth control pills along with garlic, use an additional form of birth control such as a condom.
Some birth control pills include ethinyl estradiol and levonorgestrel (Triphasil), ethinyl estradiol and norethindrone (Ortho-Novum 1/35, Ortho-Novum 7/7/7), and others.
- Cyclosporine (Neoral, Sandimmune) interacts with GARLIC
The body breaks down cyclosporine (Neoral, Sandimmune) to get rid of it. Garlic might increase how quickly the body breaks down cyclosporine (Neoral, Sandimmune). Taking garlic along with cyclosporine (Neoral, Sandimmune) might decrease the effectiveness of cyclosporine (Neoral, Sandimmune). Do not take garlic if you are taking cyclosporine (Neoral, Sandimmune).
- Medications changed by the liver (Cytochrome P450 2E1 (CYP2E1) substrates) interacts with GARLIC
Some medications are changed and broken down by the liver.
Garlic oil might decrease how quickly the liver breaks down some medications. Taking garlic oil along with some medications that are changed by the liver can increase the effects and side effects of your medication. Before taking garlic oil talk to your healthcare provider if you take any medications that are changed by the liver.
Some medications that are changed by the liver include acetaminophen, chlorzoxazone (Parafon Forte), ethanol, theophylline, and drugs used for anesthesia during surgery such as enflurane (Ethrane), halothane (Fluothane), isoflurane (Forane), and methoxyflurane (Penthrane).
- Medications changed by the liver (Cytochrome P450 3A4 (CYP3A4) substrates) interacts with GARLIC
Some medications are changed and broken down by the liver.
Garlic might increase how quickly the liver breaks down some medications. Taking garlic along with some medications that are broken down by the liver can decrease the effectiveness of some medications. Before taking garlic talk to your healthcare provider if you are taking any medications that are changed by the liver.
Some medications changed by this liver include lovastatin (Mevacor), ketoconazole (Nizoral), itraconazole (Sporanox), fexofenadine (Allegra), triazolam (Halcion), and many others.
- Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs) interacts with GARLIC
Garlic might slow blood clotting. Taking garlic along with medications that also slow clotting might increase the chances of bruising and bleeding.
Some medications that slow blood clotting include aspirin, clopidogrel (Plavix), diclofenac (Voltaren, Cataflam, others), ibuprofen (Advil, Motrin, others), naproxen (Anaprox, Naprosyn, others), dalteparin (Fragmin), enoxaparin (Lovenox), heparin, warfarin (Coumadin), and others.
- Warfarin (Coumadin) interacts with GARLIC
Warfarin (Coumadin) is used to slow blood clotting. Garlic might increase the effectiveness of warfarin (Coumadin). Taking garlic along with warfarin (Coumadin) might increase the chances of bruising and bleeding. Be sure to have your blood checked regularly. The dose of your warfarin (Coumadin) might need to be changed.
The following doses have been studied in scientific research:
- 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.