What ingredient is the reason behind the caution on Black Adder Liquorice tea?

The caution on the packet of Black Adder tea is due to the herb Liquorice root (Glycyrrhiza glabra).  Liquorice is popular herb as it has a number of positive effects on the body; helpful for respiratory conditions, as an adrenal tonic (for stress), digestion and anti-inflammatory properties. and it tastes good!

However, under some circumstances it is best to avoid it completely; such as high blood pressure, kidney problems and pregnancy. The most common effects when too much liquorice is consumed are increased blood pressure and water retention (including Liquorice sweets too!). This is why it is not recommended for those with high blood pressure or women who are pregnant (Toxemia which can occur suddenly in pregnancy and high blood pressure is part of this condition). The adrenocortical effects of this herb can lead to increased mineralocorticoid activity which in turn gives raise the retention of sodium, and thus water with the potential to raise blood pressure and cause oedema. If water retention occurs and the Liquorice consumption is stopped, the body will normalise.