A clove of garlic a day is often the amount recommended for medicinal purposes. Garlic contains an array of nutrients, but vitamins and minerals aren't the only health-bestowing substances present. Phytochemicals, naturally occurring chemicals that plants produce, abound in garlic.

Garlic's Safety

Garlic is safe for most adults. Other than that special aroma garlic lends to your breath and perspiration, the herb has few side effects. However, you should know about a few cautions:

If you are allergic to plants in the Liliaceae (lily) family, including onions, leeks, chives, and such flowers as hyacinth and tulip, avoid garlic. People who are allergic to garlic may have reactions whether it's taken by mouth, inhaled, or applied to the skin.

People anticipating surgery or dental procedures, pregnant women, and those with bleeding disorders should avoid taking large amounts of garlic on a regular basis due to its ability to "thin" the blood, which could cause excessive bleeding. Taking blood thinners such as warfarin (brand name Coumadin) or aspirin and other nonsteroidal anti-inflammatory drugs (such as ibuprofen or naproxen) along with garlic is not recommended unless you first discuss it with your health-care provider so dosing adjustments can be made. To be safe, if you have any questions about your use of garlic, talk with your health-care provider.

Because garlic can thin the blood, you shouldn't eat it before dental procedures.
(And your dentist will thank you, too.)

Garlic interferes with medications other than anticoagulants. Garlic may interact with and affect the action of birth control pills, cyclosporine (often prescribed for rheumatoid arthritis), and some other medications. It also interferes with certain HIV/AIDS antiviral medications, reducing their effectiveness. Talk with your health-care provider and/or pharmacist if you take prescription medications and regularly eat large amounts of garlic or take any type of garlic supplement.
Nursing women may find that garlic gives their milk an "off" flavor that the baby may reject, resulting in shorter nursing times.
Consuming large amounts of garlic can irritate the stomach lining and possibly cause heartburn, abdominal pain, flatulence, diarrhea, or constipation. Go easy with garlic if you have a sensitive stomach.
If applied directly to the skin, garlic can cause burns. Be especially careful using raw garlic on children's skin.
If the strong odor garlic gives your breath, perspiration, and skin bothers you, consume less of it.

The Skinny on Supplements

Fresh, naturally grown raw garlic is best, but if you can't get enough of it into your diet, here is the scoop on supplements.

Ear Infection Therapy
With Garlic
Garlic extract added to olive oil is an age-old remedy for ear infections. Herbalists recommend slightly heating the oil, adding a very small amount of sliced garlic, letting it sit for a few minutes, and then straining it thoroughly before putting a couple of drops into the infected ear.

There must be absolutely no garlic particles in the oil. Before you place the oil in the ear, place a few drops on the inside of your arm and let it sit for several minutes to be sure that it is not strong enough to burn your arm (either because of the temperature of the oil or the amount of garlic essence present). If it passes the test, put a few small drops into the infected ear. Make a fresh batch for each treatment.

It's safest to check with your health-care provider before trying this home remedy, and it is essential if you have or have ever had a ruptured eardrum.

As noted in several of the research studies mentioned, not all garlic supplements consistently have the amount of allicin claimed on the label when they undergo testing. There are many possible variables, including differences in the garlic itself, growing conditions, amounts and types of fertilizer, type of garlic, the processing methods used, and quality control during manufacturing.

This remains a problem with assessing research on garlic -- do the commercial garlic preparations contain what they say they do? Which compounds do they really have and how much is there in the supplement you're taking?

Supplements are typically made by slicing garlic and drying it at low temperatures to prevent the destruction of alliinase, the enzyme that turns alliin into the disease-fighter allicin. It is then pulverized into a powder and formed into tablets. In order to meet the standards set by the U.S. Pharmacopeia (the group that develops the quality standards for prescription and over-the-counter drugs and dietary supplements sold in the United States), the powder must contain at least 0.3 percent alliin.

Because manufacturers process and label their supplements differently, shopping for garlic supplements can be confusing. Some tablets do not contain any allicin, but rather alliin, which is converted to allicin. Other tablets contain both alliin and allicin. And some supplement labels may have an "allicin potential" or "allicin yield" statement. This refers to the amount of allicin that could be formed when alliin is converted, not how much allicin is actually formed.

In addition, because the enzyme alliinase is destroyed by the strong acidic conditions in the stomach, most supplements are "enteric coated" to keep them from dissolving until they reach the small intestine. Most tablets tested, though, produce only a little allicin under these tough conditions, and the tablets often take too long to dissolve. The better measurement is "allicin release." This discloses how much allicin the supplement actually produces under conditions similar to those found in the digestive tract. However, only a few manufacturers list this measurement on their labels.

With all this in mind, you should start by looking for the "standardization" statement on a label when choosing a garlic supplement -- but even this isn't a foolproof guarantee. When a product is "standardized" it is supposed to have a certain amount of a specific ingredient. For instance, a product that says, "standardized to contain 1.3 percent alliin" means that every pill in every bottle should contain at least 1.3 percent alliin. Unfortunately, this is not always the case, but a product that carries the USP (U.S. Pharmacopeia) seal follows set methods to help ensure standardization.

Allicin is not the only active compound in garlic, but the other compounds are typically not standardized. Thus, you often don't know everything you're getting when purchasing a supplement.

Which kind of supplement is best? Dried garlic powder is considered to have effects similar to those of fresh, crushed garlic. Other types of supplements, such as oils from crushed garlic, aged garlic extract in alcohol, and steam-distilled oils seem to contain less allicin and perhaps less of other active compounds than the dried powder.

A good garlic supplement contains at least 1.3 percent allicin.

When shopping for a garlic supplement, look for one that indicates it is standardized to contain at least 1.3 percent allicin. In the United States, pharmacy-grade garlic contains 0.3 percent (powdered form) to 0.5 percent (fresh, dried form) allicin. Avoid enteric-coated or time-release tablets because these may not dissolve soon enough in your digestive tract to make use of the allicin.

How Much Should You Take?

Large scientific boards make several recommendations about garlic dosage. The Mayo Clinic cites the European Scientific Cooperative on Phytotherapy's recommendation for prevention of atherosclerosis as 3 milligrams to 5 milligrams allicin (3,000 micrograms to 5,000 micrograms allicin) or one clove or 0.5 gram to 1 gram of dried powder.

The World Health Organization recommends 2 grams to 5 grams of fresh garlic, 0.4 gram to 1.2 grams of dried garlic powder, 2 milligrams to 5 milligrams of garlic oil, 300 milligrams to 1,000 milligrams of garlic extract, or some other formulation that yields the equivalent of 2 milligrams to 5 milligrams (2,000 to 5,000 micrograms) of allicin daily.

Go to the Clove

Rather than fussing over garlic supplements that may or may not contain what they claim, just enjoy the heady aroma and flavor of fresh garlic in the foods you eat. You'll always know you're getting the best -- and the most potent -- allicin you can when you add garlic to foods. Consider this:

A typical garlic clove weighs about 3 grams.
The amount of alliin in an average clove ranges from 24 milligrams to 56 milligrams.
A standard clove will produce about 2.5 milligrams to 4.5 milligrams of allicin per gram of fresh weight when crushed. This means you'll get 7.5 milligrams to 13.5 milligrams of allicin from one typical clove that weighs 3 grams.

Control Your Waistline
With Garlic
Studies performed on rats indicate that when fed allicin while on a sugar-rich diet, the rodents' blood pressure, insulin levels, and triglyceride levels all decrease. A study that appeared in the December 2003 issue of the American Journal of Hypertension showed other surprising results. The weight of the rats that were fed allicin either remained stable or decreased slightly. The weight of the rats in the control group increased. Certainly, additional research needs to be done, but this study again demonstrates how wide-ranging garlic's benefits could be.

The Bottom Line

Aim for about 5 milligrams of allicin per day.
Use supplements that state the amount of "allicin release" rather than "allicin yield" or "allicin potential."
When reading supplement labels, note that the amount of allicin is often listed in micrograms (mcg) rather than milligrams (mg). There are 1,000 micrograms in 1 milligram, so a supplement that contains 5,000 micrograms of allicin has 5 milligrams of allicin, which meets the European Scientific Cooperative on Phytotherapy's recommendation of 3 milligrams to 5 milligrams of allicin.
A supplement may contain 500 milligrams of dried garlic bulb, which is equal to 0.5 gram. This falls into the low end of the World Health Organization's recommendation for dried garlic powder. Remember that dried powder contains just a small amount of allicin. Other compounds make up the rest of the tablet.

But why exactly should you stink up your breath with garlic? One of the specific benefits is that it may help lower cholesterol. On the next page you'll learn what role garlic plays in the bloodstream.

Want more information about garlic? Try:

Vegetable Recipes: Find delicious recipes that feature garlic.

Nutrition: Find out how garlic fits in with your overall nutrition plans.

Vegetable Gardens: Grow a full harvest of great vegetables this year.

Gardening: We answer your questions about all things that come from the garden.

This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.