Black licorice is made from the licorice plant, a member of the bean family, found in parts of Europe and Asia. It has long been used as a folk remedy to treat a variety of illnesses. One of the active ingredients in natural licorice -- glycyrrhizin -- has both positive and potentially life-threatening side effects. Do not consume black licorice without discussing its use with your doctor.

Black licorice sold as candy may not contain the ingredients considered responsible for most of the herb’s effects, both good and bad. Black licorice candy often contains anise, which has a similar flavor to licorice but no active ingredients. Red licorice does not contain any real licorice. Black licorice can also be made with deglycyrrhizinated extract, also called DGL, which does not have the same effects as glycyrrhizin. To know if your black licorice contains the "real thing," read the label carefully.

Health benefits claimed for black licorice containing actual licorice root include improvement in lipid levels, including total cholesterol and low-density lipoprotein, the “bad” cholesterol, and triglycerides. Both DGL and licorice containing glycyrrhizin may help heal stomach ulcers, probably by preventing the breakdown of prostaglandins, which have a protective effect on the stomach. DGL, however, may have fewer serious side effects. Real black licorice may also help nausea and vomiting as well as heartburn and acid reflux. Licorice is also purported to help heal coughs and congestion, including asthma. More studies are needed to test all the claims made for licorice, UMMC states.

Licorice taken in large amounts can have serious side effects. The glycyrrhizin in black licorice can cause fluid retention, leg swelling, high blood pressure, congestive heart failure, fatigue, lethargy, headaches, muscle weakness and an increased risk of heart attack. Glycyrrhizin can also cause the kidneys to release excess amounts of potassium, the U.S. Food and Drug Administration warns, which leads to abnormal heart rhythms. Potential hormonal effects from black licorice include impotence in men, menstrual abnormalities in women and decreased sex drive in both sexes.

The FDA warns that consuming more than 2 oz. of black licorice daily, for 14 days or longer, can cause potassium levels to fall to dangerous levels. If you stop eating black licorice, potassium levels usually rise to previous levels without any long-lasting effects. Pregnant and breastfeeding women should not eat black licorice in any amount.