If you're at all concerned about your blood pressure, don't eat it.
Licorice contains glycyrrhizinic acid, a substance that sets off a chain of biochemical events in the body that result in high blood pressure.
In a nut-shell, glycyrrhizinic acid prevents a protective enzyme in the kidney from breaking down cortisol. Cortisol is often referred to as the stress hormone, and one of its roles is to tell the kidney to get rid of potassium. So eating licorice results in low potassium levels – which in turn leads to elevated blood pressure and a host of other dangerous side-effects.
Not all products labelled as licorice actually contain real licorice. If the labelling, however, includes “licorice extract” or “licorice root” it's best to avoid it.
The occasional treat won't hurt – but if you have a licorice habit, it's a habit worth breaking.