Garlic (Allium sativum) is an herb related to onion, leeks, and chives. It is commonly used for conditions related to the heart and blood system.
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 change the effects of garlic.
People commonly use garlic for high blood pressure, high levels of cholesterol or other fats in the blood, and hardening of the arteries. It is also used for the common cold, osteoarthritis, and many other conditions, but there is no good scientific evidence to support these uses. There is also no good evidence to support using garlic for COVID-19.
Is It Effective?
NatMed Pro 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.
- A painful uterine disorder (endometriosis). Taking garlic powder tablets by mouth daily for 3 months seems to improve pain in people with this condition.
- Hardening of the arteries (atherosclerosis). Taking garlic powder by mouth, alone or with other ingredients, seems to help slow hardening of the arteries.
- Diabetes. Taking garlic powder by mouth seems to reduce pre-meal blood sugar levels by a small amount in people with or without diabetes. It seems to work best if it is taken for at least 3 months. It's unclear if garlic reduces post-meal blood sugar levels or HbA1c levels.
- High levels of cholesterol or other fats (lipids) in the blood (hyperlipidemia). Taking garlic by mouth daily for at least 8 weeks might reduce total cholesterol and low-density lipoprotein (LDL, "bad" cholesterol) in people with high cholesterol levels. But any benefit is probably small. And taking garlic doesn't help increase high-density lipoprotein (HDL, "good" cholesterol) or lower levels of other blood fats called triglycerides.
- High blood pressure. Taking garlic by mouth seems to reduce systolic blood pressure (the top number) by about 7-9 mmHg and diastolic blood pressure (the bottom number) by about 4-6 mmHg in people with high blood pressure.
- Build up of fat in the liver in people who drink little or no alcohol (nonalcoholic fatty liver disease or NAFLD). Taking garlic powder by mouth seems to help to improve liver health in people with NAFLD. People who eat more garlic also seem to be less likely to be diagnosed with NAFLD.
- A serious gum infection (periodontitis). Taking aged garlic extract by mouth twice daily for 18 months can help improve gum health in people who have mild or moderate periodontitis.
- Stomach cancer. People who eat more garlic or take garlic supplements by mouth don't seem to have a lower chance of developing stomach cancer.
- A digestive tract infection that can lead to ulcers (Helicobacter pylori or H. pylori). Taking garlic by mouth does not seem to help treat H. pylori infections.
There is interest in using garlic for a number of other purposes, but there isn't enough reliable information to say whether it might be helpful.
Is it Safe?
When taken by mouth: Garlic is likely safe for most people. Garlic has been used safely for up to 7 years. It can cause side effects such as bad breath, heartburn, gas, and diarrhea. These side effects are often worse with raw garlic. Garlic might also increase the risk of bleeding and cause allergic reactions in some people.
When applied to the skin: Garlic products are possibly safe. Gels, pastes, and mouthwashes containing garlic have been used for up to 3 months. But garlic might cause skin damage that is similar to a burn. RAW garlic is possibly unsafe when applied to the skin. It might cause severe skin irritation.
Special Precautions & Warnings:
Pregnancy and breast-feeding: Garlic is likely safe to take by mouth in the amounts normally found in food. Garlic is possibly unsafe when used in medicinal amounts during pregnancy and when breast-feeding. There isn't enough reliable information about the safety of applying garlic to 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 children in doses of up to 300 mg three times daily for up to 8 weeks. There isn't enough reliable information to know if garlic is safe when used in larger doses or for longer than 8 weeks. It is possibly unsafe to apply raw garlic to the skin. It might burn the skin.
Bleeding disorder: Garlic, especially fresh garlic, might increase the risk of bleeding.
Surgery: Garlic might prolong bleeding and interfere with blood pressure. Garlic might also lower blood sugar levels. Stop taking garlic at least two weeks before a scheduled surgery.
Atazanavir (Reyataz)
Interaction Rating=Moderate Be cautious with this combination.
Garlic might reduce how much atazanavir the body absorbs. This might decrease how well atazanavir works.
Isoniazid
Interaction Rating=Moderate Be cautious with this combination.
Garlic might reduce how much isoniazid the body absorbs. This might decrease how well isoniazid works.
Medications changed by the liver (Cytochrome P450 2E1 (CYP2E1) substrates)
Interaction Rating=Moderate Be cautious with this combination.
Some medications are changed and broken down by the liver. Garlic might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.
Medications changed by the liver (Cytochrome P450 3A4 (CYP3A4) substrates)
Interaction Rating=Moderate Be cautious with this combination.
Some medications are changed and broken down by the liver. Garlic might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.
Medications for HIV/AIDS (Protease inhibitors)
Interaction Rating=Moderate Be cautious with this combination.
Taking garlic might decrease the amount of HIV/AIDS medication the body can absorb. This could decrease the effects of some medications used for HIV/AIDS.
Medications for diabetes (Antidiabetes drugs)
Interaction Rating=Moderate Be cautious with this combination.
Garlic might lower blood sugar levels. Taking garlic along with diabetes medications might cause blood sugar to drop too low. Monitor your blood sugar closely.
Medications for high blood pressure (Antihypertensive drugs)
Interaction Rating=Moderate Be cautious with this combination.
Garlic might lower blood pressure. Taking garlic along with medications that lower blood pressure might cause blood pressure to go too low. Monitor your blood pressure closely.
Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)
Interaction Rating=Moderate Be cautious with this combination.
Garlic might slow blood clotting. Taking garlic along with medications that also slow blood clotting might increase the risk of bruising and bleeding.
Saquinavir (Fortovase, Invirase)
Interaction Rating=Moderate Be cautious with this combination.
Saquinavir is a medication taken for HIV. Garlic might decrease how much saquinavir goes into the blood. This might decrease the effects of saquinavir.
Sofosbuvir (Sovaldi)
Interaction Rating=Moderate Be cautious with this combination.
Garlic might increase how quickly the body gets rid of sofosbuvir. This might decrease the effects of sofosbuvir.
Tacrolimus (Prograf)
Interaction Rating=Moderate Be cautious with this combination.
Garlic might decrease how quickly the liver breaks down tacrolimus. Taking garlic with tacrolimus might increase the effects and side effects of tacrolimus.
Warfarin (Coumadin)
Interaction Rating=Moderate Be cautious with this combination.
Warfarin is used to slow blood clotting. Garlic might increase the effects of warfarin. Taking garlic along with warfarin might increase the chances of bruising and bleeding. Be sure to have your blood checked regularly. The dose of your warfarin might need to be changed.
Herbs and supplements that might lower blood pressure: Garlic might lower blood pressure. Taking it with other supplements that have the same effect might cause blood pressure to drop too much. Examples of supplements with this effect include andrographis, casein peptides, L-arginine, niacin, and stinging nettle.
Herbs and supplements that might lower blood sugar: Garlic might lower blood sugar. Taking it with other supplements with similar effects might lower blood sugar too much. Examples of supplements with this effect include aloe, bitter melon, cassia cinnamon, chromium, and prickly pear cactus.
Herbs and supplements that might slow blood clotting: Garlic might slow blood clotting and increase the risk of bleeding. Taking it with other supplements with similar effects might increase the risk of bleeding in some people. Examples of supplements with this effect include ginger, ginkgo, nattokinase, and Panax ginseng.
There are no known interactions with foods.
Garlic has most often been used by adults in doses of 2400 mg by mouth daily for 12 months. Garlic extracts are usually standardized by the amount of allicin they contain. This typically ranges from 1.1% to 1.3%. 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. Garlic is also used in creams, gels, pastes, and mouthwashes. Speak with a healthcare provider to find out what dose might be best for a specific condition.
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