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Garlic contains a number of nutrients, and a number of sulfur compounds that have been shown to have medical qualities, especially allicin and alliin.

The sulfur compounds present in garlic may increase phase II detoxification enzymes. By increasing phase II enzymes, the risk of many degenerative conditions may be reduced significantly.

Allicin, one of the active ingredients in garlic, has been shown to have antimicrobial qualities that may be more effective than tetracycline. While garlic is an effective antibiotic when it contacts the tissue directly, there is no reason to believe it will work to fight infections systemically if you take it orally. There is no question raw garlic can kill a wide variety of microorganisms by direct contact, including fungi, bacteria, viruses, and protozoa. This may explain why applying garlic directly to a wound was traditionally done to prevent infection. However, garlic can cause burns when it is applied to the skin.

Therapeutic Uses
Garlic has also been proposed as a treatment for asthma and diabetes. Eating garlic is commonly claimed to raise immunity. In people, several large studies strongly suggest a diet high in garlic can prevent cancer. In one study, women whose diets included significant quantities of garlic were approximately 30 percent less likely to develop colon cancer. The interpretations of studies like this one are always a bit controversial; as it’s possible the women ate a lot of garlic but also made other healthful lifestyle choices.

Moderately good studies have found garlic (including garlic powder) also appears to slightly improve hypertension in people and pets, protect against free radicals, and slow blood coagulation. Putting all these benefits together, garlic may be a broad-spectrum treatment for arterial disease. Garlic can be used for allergic dermatitis as it contains chemicals that can reduce the production of inflammatory prostaglandins.

It is also a cardiovascular tonic and can help prevent blood clots. The cholesterol-reducing effects of garlic may also be helpful for pets with heart disease or high blood cholesterol.

Garlic has been used to control fleas and some owners report positive results.

It is recommended for pets with tapeworms and has shown effects against roundworms and hookworms in people.

Scientific Evidence
Garlic has been shown to stimulate white blood cells (killer cells) in human AIDS patients. And also shown to prevent tumor formation in rats (due to its diallyl sulfide component and due to its liver-strengthening chemicals).

Garlic can decrease blood cholesterol and triglyceride levels; certain forms of garlic have been shown to lower total cholesterol levels by nine to twelve percent, as well as possibly improve the ratio of good to bad cholesterol. Virtually all studies in people used garlic standardized to alliin content, whereas garlic oil did not seem to be effective; conflicting results have been shown for garlic powder, although some results are encouraging.

Allicin is not necessary for all of garlic’s purported benefits but is needed to confer the antibiotic properties of garlic. When used for infections, the allicin potential of the garlic compound used is important. Since allicin is an unstable compound that is easily destroyed, fresh garlic or products with an identified allicin potential should be used. Because it is hard to know if a prepared formula has the guaranteed amount of allicin listed on the label unless the product comes from a reputable manufacturer, many herbalists recommend using fresh garlic cloves when the content is important. For prepared products, the product should provide a daily dose of at least 10 mg alliin or a total allicin potential of 4000 micrograms (4–5 mg), which approximates one clove of garlic. In people a typical dosage of garlic is 900 mg daily of a garlic powder extract standardized to contain 1.3 percent alliin, providing about 12,000 mcg daily. This recommendation needs to be extrapolated for use in pets. Many manufacturers claim an allicin potential at the time of manufacture. This is not helpful, as it does not reveal the allicin potential of the finished product and whether or not the product is stable. Read labels carefully.

However, a great deal of controversy exists over the proper dosage and form of garlic. In people, most everyone agrees one or two raw garlic cloves a day are adequate for most purposes. Virtual trade wars have taken place over the potency and effectiveness of various dried, aged, or deodorized garlic preparations. The problem has to do with the way garlic is naturally constructed.

A relatively odorless substance, alliin is one of the most important compounds in garlic. When garlic is crushed or cut, an enzyme called allinase is brought in contact with alliin, turning it into allicin. The allicin itself then rapidly breaks down into entirely different compounds. Allicin is most responsible for the strong odor. It can also blister the skin and kill bacteria, viruses, and fungi. Presumably, the garlic plant uses allicin as a form of protection from pests and parasites. It also may provide much of the medicinal benefits of garlic.

Some garlic producers declare alliin and allicin have nothing to do with garlic’s effectiveness and simply sell products without it. This is particularly true of aged powdered garlic and garlic oil. But others feel certain allicin is absolutely essential. However, to make it relatively odorless, they must prevent the alliin from turning into allicin until the product is consumed. To accomplish this feat, they engage in marvelously complex manufacturing processes, each unique and proprietary. How well this works is a point of controversy.

The best that can be said is that in most studies that found cholesterol-lowering powers in garlic, the daily dosage supplied at least 10 mg of alliin. This is sometimes stated in terms of how much allicin will be created from that alliin. The number you should look for is 4 to 5 mg of allicin potential. Alliin-free aged garlic also appears to be effective when taken at a dose of 1 to 7.2 g daily.

To use garlic for other uses such as cancer, antioxidants, nutritional supplement, or immune booster, any form will probably work if the garlic has not been subjected to extreme heat (such as roasting). Raw garlic cloves are probably preferred.

Safety Issues
Too much garlic can be toxic to pets, causing Heinz body anemia. As a rule, I recommend following label directions for commercially prepared products. For feeding fresh garlic, I use one clove per 10 to 30 pounds of body weight per day. There do not appear to be any animal toxicity studies on the most commonly used form of powdered garlic standardized to alliin content.

Do not use in pets with anemia. Do not use in pets scheduled for surgery due to increased bleeding times. Refrain from use at least one week before and one week after surgery. Topical garlic can cause skin irritation, blistering and even third-degree burns, so be very careful about applying garlic to the skin.

Garlic may cause intestinal gas. Reduce dosage if this occurs.

Taking garlic at the same time as taking ginkgo or high-dose vitamin E might conceivably cause a risk of bleeding problems.

Shawn Messonnier, DVM

As my thank you for reading my articles, enter code “drshawn” at my natural products web store,, to save 10% on all your future purchases!

Shawn Messonnier DVM Past Supporting Member, Oncology Association of Naturopathic Physicians Author, the award-winning The Natural Health Bible for Dogs & Cats, The Natural Vet’s Guide to Preventing and Treating Cancer in Dogs, and Breast Choices for the Best Chances: Your Breasts, Your Life, and How YOU Can Win The Battle!

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