Eating more than 57g (two ounces) of black liquorice a day for at least two weeks could lead to potentially serious health problems, such as an increase in blood pressure and an irregular heart rhythm (arrhythmia).
Black liquorice contains glycyrrhizin, which is a sweetening compound taken from liquorice root. Glycyrrhizin can cause potassium levels in the body to fall. Potassium is a mineral that's essential for normal heart activity.
Decreased potassium levels can lead to some people experiencing abnormal heart rhythms, as well as high blood pressure, oedema (swelling), lethargy and heart failure. Potassium levels usually return to normal with no permanent health problems when you stop eating black liquorice.
For most people, liquorice found in foods is safe to eat and safe when consumed in large amounts in medicines for short periods of time.
General health advice about black liquorice
No matter how old you are, you should avoid eating large amounts of black liquorice over a short space of time.
If you've been eating a lot of black liquorice and have heart palpitations, muscle weakness, or other health-related problems, stop eating it immediately and seek medical advice.
Black liquorice can interact with some medications, herbs and dietary supplements. See a healthcare professional, such as a primary-care doctor or pharmacist, if you have questions about possible interactions with a medication or supplement you're taking.