Nation Eating too much black licorice can be dangerous. Should you be worried this Halloween? October 31, 2019 N'dea Yancey-Bragg, USA TODAY Comments Off on Eating too much black licorice can be dangerous. Should you be worried this Halloween? A compound in black licorice called glycyrrhizin can cause abnormal heart rhythms, high blood pressure and congestive heart failure, the FDA says.