There is some truth to that statement. In susceptible individuals, licorice can indeed elevate blood pressure. In individuals who have a history of hypertension, licorice can aggravate the hypertension if taken in excess amounts. The mechanism is that licorice inhibits the enzyme (11-B hydroxysteoid dehydrogenase) that allows cortisol (the body’s natural stress hormone) to be metabolized into cortisone. Therefore, elevation of cortisol results in high blood pressure.
In normal individuals with no history of high blood pressure, licorice intake has not been shown to have a marked effect on blood pressure.