Adult trick-or–treaters should not eat too much black licorice because that can lead to heart arrhythmias and other health problems, warns the Food and Drug Administration.
Experts say that consuming two ounces of black licorice per day for two weeks can cause irregular heartbeats.
The ingredient that causes the problem is glycyrrhizin, which gives black licorice its sweet taste.
Glycrrhizin causes the kidneys to excrete potassium, which can cause abnormal heart beats and high-blood pressure in susceptible adults.
When combined with certain medications, such as diuretics and laxatives, black licorice can cause adverse reactions.
Though black licorice is most dangerous for adults 40 and older, everyone, including children, should eat the old-fashioned favorite in moderation, says the FDA.