What is licorice?
First of all, if you're looking for the kind of licorice that serves as an herbal medicine, forget about the red and black sticks in the candy aisle. In the United States, so-called licorice candy is almost always flavored with anise and contains no actual licorice.
Real licorice, which comes from the root of the plant Glycyrrhiza glabra, tastes just as sweet as the impostors but packs a bigger punch. Since ancient times, people have used licorice -- or, more to the point, its active ingredient, glycyrrhizic acid -- for coughs, colds, and other ailments, and modern herbalists claim it also speeds the healing of stomach ulcers and prevents cancer.
Does licorice really work?
The flavorful root seems to have some impressive powers. Japanese researchers have found that a medicine containing glycyrrhizic acid helped prevent liver cancer in patients with hepatitis C. And according to the Complete German Commission E Monographs, the modern bible of herbal medicine, licorice really can help stomach ulcers heal. (A Chinese study found that it slows the growth of Helicobacter pylori, the bacterium that causes about 80 percent of all stomach ulcers.) The commission also says that licorice eases inflammation in the airways, which makes it a potentially useful for people with chronic rhinitis. And although researchers aren't certain whether it relieves coughs, the herb can loosen mucus in the lungs and help clear congestion.
Is licorice dangerous?
It may be all-natural and decadently sweet, but licorice is also a potent medicine that can cause serious side effects. In his book The Honest Herbal, Varro Tyler cautions that large doses of it can cause headaches, reduced energy, salt and water retention, potassium loss, high blood pressure, heart failure, or cardiac arrest.
If you decide to try licorice, don't consume more than 15 grams of the root (or 600 milligrams of glycyrrhizic acid) in a day, and don't take it for longer than six weeks. In people who are particularly sensitive to it, just 2.5 grams of the root can trigger side effects. The small levels of licorice found in tobaccos, lozenges, and real licorice candies are generally safe -- but it's still possible to overdo it. The British Medical Journal reported in the 1970s that healthy volunteers who ate 100 to 200 grams (about one-fifth to two-fifths of a pound) of real licorice twists every day came down with serious side effects within four weeks.
To be safe, you should avoid the herb completely if you're pregnant or nursing, or if you have high blood pressure, heart trouble, weak kidneys, hypokalemia (a shortage of potassium in the blood), or cirrhosis of the liver.
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