Liquorice-root extract contains the natural sweetener glycyrrhizin, which is over 50 times sweeter than sucrose. This ingredient has various pharmaceutical properties, the most important ones being that it acts as an expectorant and that it increases blood pressure. The latter effect can become significant with a daily consumption of 50 g or more of liquorice candy for as little as two weeks.

Liquorice has several varied uses in herbal medicine, such as acting as a mild laxative by increasing prostaglandins.

Comparative studies of pregnant women suggest that excessive amounts of liquorice (100 g a week) may adversely affect both IQ and behaviour traits of offspring.

Some people report that black liquorice candy causes their stools to become green, although this is probably due to the blue food colouring used by many manufacturers.

An excessive amount of black liquorice consumption can cause a chloride-resistant metabolic alkalosis.

The U.S. Food and Drug Administration (FDA) advises that black liquorice contains the compound glycyrrhizin, which is the sweetening compound derived from Licorice root.

Glycyrrhizin can cause potassium levels in the body to fall. some people experience abnormal heart rhythms, as well as high blood pressure, edema (swelling), lethargy, and congestive heart failure.