I HATE Black licorice with a passion. I've always thought of it as the "skunk" of candies.
It has a chemical compound called glycyrrhizin. If you have too much of it, it can increase your blood pressure, mess with your heart rhythm. It even cause heart failure.
How much black licorice could put you in danger? According to the FDA, if you eat two ounces of black licorice every day for at least two weeks, that's when you could start having problems. But chances are IF you like it, you may eat more of it than a normal person.