A Halloween-themed PSA from the Food and Drug Administration (FDA) warns that people should steer clear of eating too much black licorice because it contains a certain compound that will make you very ill if you ingest too much of it too quickly. The compound in question, glycyrrhizin, is a sweetener found naturally in the licorice root, but it can cause your body's potassium levels to fall and set off a series of issues. Specifically, it can cause you to experience an abnormal heartbeat, high blood pressure, lethargy, swelling, or congestive heart failure
According to the agency, If you’re 40 or older, eating two ounces of black licorice a day for at least two weeks could land you in the hospital with an irregular heart rhythm or arrhythmia. It also warns that the stuff can interact with some medications, herbs, and dietary supplements, and that you should seek medical attention or consult a doctor if you "experience any problems" after eating licorice.