The term "adaptogen" refers to plants or other substances that augment non-specific resistance in the body, and help the body to adapt to various situations, therefore protecting it from stressful events and factors. (Mendes, Elisaldo, Carlini., 2007). According to Brekhman II & Dardymov IV., (1969), there are 3 criteria that need to be met before a compound can be considered an adaptogen;
It must produce a nonspecific response in the body
It must produce a normalising influence on physiology in the face of a stressor
It must be incapable of influencing normal body functions more than required to gain non-specific resistance
Glycyrrhiza glabra, and G. uralensis have both been used traditionally as an adaptogen, which mainly involved its addition to traditional Chinese formulas to strengthen the body overall (Zhu, Y. P. 1998). The traditional well-rounded and non-specific indications for this herb has provoked numerous studies around the mechanisms of action as an adaptogen.
Licorice was shown to provide antidepressant activity when a study revealed licorice extracts ability to reverse diazepam, scopolamine, and ethanol induced amnesia in mice (Parle, Dhingra, & Kulkarni, 2004). The actions are suggested to be due to the cholinergic improvements in the brain, which have been reported in separate studies in doses as low as 150 mg/kg (Sigurjonsdottir, Manhem, Axelson, & Wallerstedt, 2003). In addition, the hydrophobic flavonoids of licorice root have been shown to produce abdominal fat lowering and hypoglycemic effects (Nakagawa, Kishida, Arai, Nishiyama, Mae, 2004). Both of these actions suggest the potential for adaptogenic action in the body due to marked improvements and increased tolerance to external stresses and changes in homeostasis.
There are a number of problems with the classification of licorice as an adaptogen, however, such as the influence it has on cortisol levels throughout the body. Most adaptogenic substances that buffer the stress response, act on the hypothalamus, pituitary, adrenal (HPA) axis. This is because this system is one of the key components of the “stress system” (Guilliams, & Edwards, 2010). In most cases, such as with the South American herb Pfaffia paniculata, the effects on hormones are bidirectional, allowing the herb to successfully balance the stress response in both overactive and underactive states (Masami & Gu. 2003).
In the case of licorice, the main constituent affecting the stress response is glycyrrhizin, which is structurally similar to endogenous corticosteroids. This constituent has been shown to block 11-beta-hydroxysteroid dehydrogenase which is the enzyme responsible for the conversion of cortisol to cortisone, thereby inactivating the molecule (Heilmann, Heide, Hundertmark, Schöneshofer., 1999; Krähenbühl, hasler, Frey, Frey, Brenneisen, Krapf., 1994; Whorwood, Sheppard, Stewart., 1993). As cortisol is prevented from breaking down in the body, levels will increase which can lead to a number of negative side effects over time including memory deficits (Lupien, de Leon, De Santi, Convit, Tarshish, Nair, & Meaney., 1998). This single direction activity has been shown to increase blood pressure in both healthy, and hypertensive patients to the same degree (Belinky, Aviram, Mahmood, & Vaya, 1998). The German Commission E suggests that liquorice extracts should not be taken for any longer than 6-8 weeks without professional supervision (German Federal Minister Of Justice, 1991).
The deglycyrrhizinated licorice extracts have this cortisol increasing component removed, and offers a much clearer benefit for those experiencing hypertension. This version of licorice is likely to be the better adaptogenic compound due to the reduction of the most major side effects of licorice.
The adaptogenic qualities may be caused by other components in the plant. An example of which involves the isoflavonoid glabridin which has been shown to increase the fatigue resistance of mice pretreated with the extract over a 28 day period (Van Uum, Hermus, Sweep, Walker, Ross, De Leeuw, & Lenders., 2002).
The classification of licorice as an adaptogenic medicine appears to be based mainly off traditional medical uses rather than current and concrete scientific evidence. The glycyrrhizin content and associated single direction activity and numerous negative side effects effectively eliminate it from the protocols set to determine adaptogenic compounds on the market as per the guidelines set by Brekhman, & Dardymov (1969). Licorice may have many useful attributes medicinally but is not recommended for adaptogenic uses due to lack of comprehensive research outcomes and authoritative suggestions against long-term use.