Garlic is considered an herb and a vegetable and the bulb can be used for medicinal purposes. It originally came from central Asia. Supplements are made from fresh, dried, or aged garlic extracts, as well as garlic oil. [1, 2, 3]
- Garlic essential oil: This comes from passing steam through garlic.
- Garlic oil macerate: Products are made from ground garlic cloves mixed with vegetable oil and put into capsule form.
- Garlic powder: Garlic cloves are crushed, dried and then ground to make the powder. Since the ingredients don't change, the benefits also stay the same.
- Garlic extract: This comes from alcohol-soaked garlic cloves. Extracts come in liquid and powder form.
A brief history of garlic use
Garlic has been used for thousands of years for nutritional and medicinal purposes, dating back to ancient Egyptian times. It was also used in France during the 1700s to help stave off the plague. And, it was utilized during both world wars to prevent gangrene.
These days, besides adding flavor to food, garlic is used for:
- Heart disease prevention
- High cholesterol
- High and low blood pressure
- Liver function maintenance
- High and low blood sugar
- Immune system enhancement
- Cancer prevention
- Fighting free radicals that damage DNA, cell membranes, advance aging, and possibly lead to chronic health problems
- Enlarged prostate
- Traveler's Diarrhea
- Pre-eclampsia (high blood pressure during pregnancy)
- Cold and flu
- Immune system
- Tick and snake bites
- Infection prevention and treatment
Please note that this is not an exhaustive list.Ask your healthcare provider if you might benefit from dietary or supplemental garlic.
As for dosages, it varies depending on age, diagnosis, and form used. Consult your doctor for specific dosing recommendations. [1, 2, 3]
Allicin, a chemical in garlic that gives it its odor and is also credited for its potential health benefits, varies within the herb depending on how it's processed. Aging garlic to get rid of its odor also results in reduced allicin content. Crushed and capsuled garlic have more allicin. Garlic is high in sulfur, but also arginine, flavonoids, oligosaccharides, and selenium, which may provide health benefits.
Garlicmay be effective for: [1, 2, 3]
- Heart disease prevention
- Lowering blood pressure (garlic powder)
- Killing bacteria, including those that cause food poisoning (fresh only)
- Colon, rectal, prostate, pancreatic, intestinal, and stomach cancers (dietary only, not supplements)
- Tick bites (dietary only)
- Skin tumors (garlic extract)
- Fungal infections (garlic gel with 1% ajoene)
- Immune system function during cancer
Garlicdoes not seem to work for: 
- Helicobacter pylori bacteria treatment (ulcer-causing)
- High cholesterol
- Breast and lung cancers
- Leg pain due to poor circulation
There is not enough evidence to recommend garlic for: [1, 2]
- Benign prostatic hyperplasia
- Prostate cancer
- Ringworm and other intestinal parasites (garlic gel may work)
Do not take the following medications with garlic without first checking with your healthcare provider:[1, 2]
- Isoniazid (for tuberculosis)
- Birth control pills
- Blood thinners
- Nonsteroidal anti-inflammatory drugs (NSAIDs)
Side effects and safety
- You may experience different effects depending on which form of garlic you use.
- Herbs may bring on side effects and interact with other herbs, medications, and supplements.
- Consult a qualified botanical medicine professional for questions regarding the the safe use of garlic and other herbs for medicinal purposes.
- If you have an ulcer or thyroid issues, talk to your doctor before using garlic.
- Bad breath, burning sensation in the mouth, heartburn, gas, nausea and vomiting, body odor, and diarrhea are some side effects of taking garlic.
- To prevent excess bleeding, do not take garlic for two weeks prior to schedule surgery.
- A garlic poultice can cause skin damage.
- Avoid garlic if you are pregnant or breastfeeding.
- Do not take garlic if you have a bleeding disorder.
- Beware of garlic if you have trouble with digestion or stomach issues.
- Garlic may increase insulin in your body.
- Do not take garlic if you are allergic to it.
- Commercial garlic oil capsules have vegetable oil but not much essential oil because of the smell.
- The active ingredients in garlic may lose their usefulness via processing and as they age.
- Garlic products vary regarding ingredients, strength and effects.
- The National Cancer Institute doesn't recommend supplementation for cancer prevention, but does acknowledge that garlic contains elements that have cancer fighting abilities.
University of Maryland Medicinal Center; "Garlic;" Reviewed 2011
WebMD.com; "Garlic;" WebMD.com
National Cancer Institute, Fact Sheet; "Garlic and Cancer Prevention;"