Herbs & Supplements

Should I take it?

Garlic has been highly prized--both for flavoring and for medicine--since ancient times. Believed to have originated in eastern Asia, it is now grown and used in nearly every country. It belongs to the same family of aromatic plants as chives, leeks, and onions. Flowers such as lilies are also related to garlic. Depending on the species of garlic, plants may be as tall as 3 feet or as small as about half a foot. All garlic plants have long, thin, grass-like leaves that surround a central stem. After white, pink, purple, or reddish flowers bloom during the summer and early fall, a large underground part known as a bulb develops. The bulb, which can be as large as a person's fist for some types of garlic, easily breaks into smaller pieces that are called cloves. Although garlic leaves are used as food in some areas of the world, the cloves are most used for flavoring and medicines. Often, garlic cloves are added to cooking oils to preserve the garlic and flavor the oil. In some areas, garlic oil is applied to the skin as a repellant for biting insects.

Although garlic contains many different chemicals, the sulfur compounds and volatile oils that give garlic its strong smell also account for much of its medical value. Also called essential oils, volatile oils possess the characteristic smell and taste of the plant. Volatile oils usually evaporate quickly at room temperature.

Dosage and Administration

Around the world, supplemental garlic is sold in a number of different forms--including capsules, concentrates, extracts, liquids, powders, raw garlic bulbs, and tablets. Fresh garlic juice and syrups made from fresh garlic are used more for medicine in Europe and Asia than in the United States. Some garlic products are aged to reduce odor or to allow the formation of additional chemical compounds. Some reliable evidence suggests that heat may reduce some or all of garlic's effectiveness, so preparations that are manufactured without being heated may retain more of the chemicals that are thought to be beneficial.

In this country, garlic preparations are most often available as capsules or tablets made from dried garlic powder or as aged garlic extract. Made by crushing garlic and letting it mature in a cool place for up to 20 months, aged garlic extract has fewer irritating, odor-causing chemicals than fresh garlic. Either dried or aged garlic products are marketed in several strengths and in multiple combinations with other herbal ingredients such as echinacea or ginkgo. Garlic preparations should be standardized to contain between 0.5% and 1.3% of alliin, one of the sulfur compounds in it. Standardization by the manufacturer should assure the same amount of active ingredient in every batch of the commercial preparation. Standardization of herbal products is not required by the U.S. Food and Drug Administration (FDA), so not every product sold in this country will contain the same amounts of active ingredients.

The recommended supplemental dose of garlic is 600 mg to 900 mg daily, usually taken in three or four doses during the day. Individuals who choose to take a garlic supplement should follow the directions for the product that is purchased. Virtually no limits are placed on the consumption of dietary garlic, however--with reported continual daily amounts of several ounces being common among Asian cultures whose members regularly consume garlic plants as a vegetable.

Fresh garlic varies in the amounts of active ingredients it contains depending on the location and conditions in which it is grown and the way it was processed and stored. For those who prefer using it, one-half to three cloves of raw garlic can be chewed up to three times a day. Cooking may destroy some of the medicinally effective chemicals in garlic, so garlic used in seasoning foods may not be as beneficial to health as commercial supplements or raw garlic.

Summary

Some limited clinical evidence seems to show that garlic taken orally can help moderately to reduce high cholesterol and high blood pressure. Less evidence supports its effectiveness in preventing heart disease, enhancing immune function, and protecting against some types of cancer.

Risks

Garlic in recommended amounts seems to have few risks. People who have bleeding disorders or who take medications to thin the blood, should be aware that taking large amounts of garlic may further reduce the blood's ability to clot.

Side Effects

In the amounts used in food or recommended medicinal doses, garlic has few side effects. Large amounts, however, have been associated with irritated mouth or stomach. A few people may have asthma or rash from handling the garlic plants for a long time or in large amounts. If it is left in contact with the skin for extended periods of time, garlic may cause irritation or burns.

Interactions

If it is taken at the same time as drugs or other herbs that "thin the blood"' very large amounts of garlic taken by mouth could increase the amount of time that blood needs to clot. Garlic in high amounts may interfere with some antiviral and antidiabetic medications, as well as with other drugs, such as acetaminophen, that are broken down by the same liver enzymes as garlic. It may increase the activity of drugs that lower blood sugar.

Last Revised April 11, 2008