Liquorice (licorice) is a root extract of the Glycyrrhiza Glabra plant. This plant contains a number of phytochemicals including the terpenoid saponin glycyrrhizin (also known as glycyrrhizic acid) and a number of flavonoids including liquiritin, isoliquiritin, liquiritigenin and isoliquiritigenin. Liquorice may affect neurochemistry, and this may in part relate to the fact that glycyrrhizin can interact with the stress hormone response and thereby may modulate levels of cortisol. The flavonoid components of liquorice may also confer neuroprotective effects. A number of studies have investigated liquorice as a treatment for anxiety and some evidence suggests that liquorice may work synergistically with other anxiolytic herbs. For example, in one study researchers administered valerian extract to mice and exposed them to experimental stress. As had been shown previously, valerian significantly reduced the anxious behaviour of the mice. Alazopram, a benzodiazepine drug also had a significant anti-anxiety effect on the nice.
Components from liquorice may inactivate 11-Hydroxysteroid dehydrogenase type 2 (11-HSD2). This enzyme rapidly regrades glucocorticoids in the placenta. By inhibiting this enzyme, liquorice may increase the permeability of the placenta to glucocorticoids. There may be similar effects on isoforms of this enzyme in other tissues including the blood-brain barrier and the gastrointestinal tract.
However, when the researchers administered the valerian with liquorice extract, they found a significant synergistic anxiolytic effect on the behaviour of the mice. Likewise, when liquorice was administered in combination with alazopram, there was a significant synergistic anxiolytic effect on the behaviour of the mice. The authors concluded that the results of the study support the contention that liquorice extracts potentiate the activity of known anxiolytic drugs. They speculated that one mechanism of action may be an increase in the blood brain barrier permeability or an increase in the absorbance in the gastrointestinal tract. The ability of components of liquorice to increase the permeability of tissues has been previously reported. For example, liquorice may increase the permeability of the placental barrier to glucocorticoids during pregnancy in humans and animals. The effects of liquorice of mood disorder could therefore include a change to the blood-brain barrier or gut permeability.
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