Adaptogenic plants have long been used in traditional medicine to enhance our body’s defense systems and promote physical and mental well-being. In this article, we review the mechanisms of action and safety of adaptogenic herbs. We also review which adaptogenic herbs have shown the best effects in human studies.
Adaptogenic plants have a long history of use as promoters of physical and mental health and enhancers of the body’s defense mechanisms.
The concept of “adaptogen” was first coined at the end of the 1950s by the Russian toxicologist Nikolay V. Lazarev to define compounds with the ability to increase “the state of non-specific resistance” of an organism to stress.(1,2) Later, Brekhman and Dardimov(3) added to the concept by stating that a compound or preparation should be considered an adaptogen only if it meets the following requirements:
“(a) an adaptogen should be innocuous and cause minimal disorders in the physiological functions of an organism; (b) the action of an adaptogen should be nonspecific, i.e., it should increase resistance to adverse influences of a wide range of factors of physical, chemical and biological nature; (c) an adaptogen may possess normalizing action irrespective of the direction of the foregoing pathologic changes.”
In other words, an adaptogen should be safe, non-toxic, increase resistance to all kinds of stressors, and have a normalizing effect on the organisms independent of the direction of the adverse shift.
More recently, Panossian and Wilkman(4) defined adaptogens as:
“anti-fatigue drugs that: (i) induce increased attention and endurance in situations of decreased performance caused by fatigue and/or sensation of weakness, and (ii) reduce stress-induced impairments and disorders related to the function of stress (neuroendocrine and immune) systems.”
Fatigue is can be defined as a general feeling of tiredness and lack of energy. This state of mental and/or physical exhaustion is a common consequence of stress that manifests as decreased attention, decreased focus, and increased sleepiness. This leads to an incapacity to function at a normal level of performance. Adaptogens confer stress-protection and battle fatigue by stimulating the central nervous system. Their stimulating effect is more pronounced against a background of fatigue and stress.(5) One of the main advantages of adaptogens is that they are safe for long-term use, they do not cause addiction or tolerance and they do not have abuse potential.
Main mechanisms of action of adaptogens
Adaptogens exert their effects by regulating and supporting the adaptive stress response and the homeostasis—the state of balanced, dynamic equilibrium—of the neuroendocrine and immune systems. Their stress-protective action is tightly associated with the function of the hypothalamic-pituitary-adrenal (HPA) axis and the regulation of the mediators of the stress response.(5,6)
The HPA axis is activated by stress, triggering a neuroendocrine response and the release of chemical mediators and stress hormones. Stress hormones then act on the brain and other organs to promote metabolic and neurochemical changes needed for the adaptation to stress. But in a context of persistent stress, chronically high levels of chemical mediators and stress hormones leads to detrimental effects on brain function. Adaptogens act by promoting the homeostasis of the HPA axis.(5,6)
Adaptogens decrease the levels of stress-induced cortisol secretion,(6) the main stress hormone involved in the HPA axis regulation of the stress response.(7) Continuously high levels of cortisol caused by chronic stress are associated with fatigue, depression, and impaired cognitive function, including decreased attention, focus and learning ability.(8) Adaptogens also regulate the activity of glucocorticoid receptors (GR), the receptor to which cortisol and other glucocorticoids bind to exert their actions and influence cortisol secretion through feedback regulation. (5,6)
Additionally, adaptogens regulate the production of other molecules involved in the modulation of homeostasis such as: the heat shock proteins of the HSP70 family (HSP70, HSP72), which are produced as a defense response to stress and are involved in stress-induced cellular protection and in adaptation to stress; the neuropeptide Y (NPY), which upregulates HSP70 production and stimulates adaptive and stress-protective effects; nitric oxide (NO), an intracellular signaling molecule that mediates stress response and modulates stress-induced activation of hormonal, nervous, and immune systems; signaling molecules such as c-Jun N-terminal protein kinases (JNKs), that regulate cellular functions involved in the stress response.(9) Chronic stress also affects the activity of mitochondria, decreasing the biosynthesis of ATP, the primary cell energy source, and increasing the production of reactive oxygen species.(10) This leads to metabolic imbalances and oxidative stress, which contribute to the development of fatigue and cognitive impairment.(11) By supporting mitochondrial activity, adaptogens support cellular energy-generating pathways and decrease oxidative stress, thereby decreasing fatigue and improving mental performance.(4)
The best herbal adaptogens based on human studies
There are many plant extracts that have been described as adaptogens. Despite having been used in traditional medicine for centuries, many lack evidence-based reports of efficacy. Among the plant extracts that have accumulated evidence of their adaptogenic effects, most have been studied most extensively in animal research.
However, there are a few adaptogenic plant extracts that have been studied in placebo-controlled, double-blind human trials and that have consistently shown good effects in enhancing resistance to stress, combating stress-related mental and physical fatigue, increasing attention, concentration, mental performance and endurance during stress-induced fatigue. Their efficacy has also been further supported by the growing understanding of their mechanisms of action and of how adaptogens promote homeostasis. (3–5,9,12–14)
Based on scientific review articles on adaptogenic plant extracts that assessed the available data regarding their efficacy in humans, safety and mechanism of action, there are a few that stand out:(3–5,13)
1. Rhodiola rosea
(Arctic root, golden root, rose root)
The potent adaptogenic effect of Rhodiola has been repeatedly demonstrated in clinical trials. Rhodiola regulates the neuroendocrine response to stress, mitigates the detrimental effects of stress, reduces stress-induced mental and physical fatigue, and promotes cognitive function. Rhodiola has been shown to have an anti-fatigue effect in contexts of physical, emotional, and mental exhaustion. Rhodiola can improve attention, capacity for mental work, and mental performance in contexts of fatigue even after a single administration. Rhodiola also has antidepressant effects.
2. Eleutherococcus senticosus
(Siberian ginseng, eleuthero)
Eleuthero administered healthy human subjects in normal and stressful conditions (e.g., high-temperatures, extended work periods, extreme working conditions, heavy physical burden, intense mental work and physical work) improved the physical and mental work capacities in all cases. Eleuthero has been shown to have an anti-fatigue effect, reduce mental stress, and improve concentration and memory after repeated administration.
3. Panax ginseng
(ginseng, Asian ginseng, Chinese ginseng, Korean ginseng)
Panax ginseng has an anti-fatigue effect. It has been shown to improve the ability to perform mental arithmetic after repeated administration. An improved quality of life after continued intake of ginseng has also been reported.
(link to article on ginseng – to be done)
4. Schisandra chinensis
Schisandra has been shown to reduce fatigue and weakness and increase endurance and mental performance in a context of mental fatigue. Schisandra increases endurance and mental performance even after a single administration.
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